Lesson - 4 Weather forecasting

Learning Outcomes
At the end of this topic, you must be able to:
Forecast anticipated local weather from synopsis and prognosis information received,
the
movement of meteorological systems, knowledge of local influences, observation of
local
conditions and movement of own ship

Maritime activities are always risky, but there are many things that mariners and
seamen
can do to reduce the risks. Weather is one of several factors that cause maritime work
and
recreation to be risky and dangerous, but forecasting the weather can help prevent
accidents
that lead to shipping and cargo losses, injuries, and even fatalities.
Weather can be difficult to predict, especially on waterways, but good forecasting can
help ships and their crews navigate and make decisions that reduce risks. Bad weather
can
cause ships and boats to capsize, to run aground, or to collide with other ships or
objects.
Knowing what kind of weather is coming is extremely important in making maritime
activities
safer.
Weather forecasting is the application of current technology and science to predict
the
state of the atmosphere for a future time and a given location.
Weather forecasts are made by collecting as much data as possible about the current
state of
the atmosphere (particularly the temperature, humidity and wind) and using
understanding of
atmospheric processes (through meteorology) to determine how the atmosphere
evolves in the
future.
Accurate weather forecasts are very important for sailors. Their predictions determine
whether we set off on a passage, or wait for better weather. The information is used to
pick a
safe anchorage in which to shelter from a storm, or to identify a nice day to go for a
cruise with
friends.
The current weather is observed from weather stations on land, weather buoys at sea
and
satellites in space. This is standardized by the World Meteorological Organization – a
specialized
agency of the United Nations to facilitate the global exchange of weather information. A
good
example of a local weather station is the Lyttelton Port Company weather page
providing
current and past weather statistics and a 48 hour forecast.
Weather affects nearly everyone nearly every day.
Weather forecasts are issued:
To save lives
Reduce property damage
Reduce crop damage
To let the general public, know what to expect
Forecast are often utilized to make many important decisions on a daily basis
How is weather forecast made?
Creating forecasts is a complex process which is constantly being updated
It involves the application of technology and detailed meteorological knowledge of how
the
atmosphere, the Earth’s surface and the oceans work.
Modern weather forecasting applies scientific knowledge to predict future atmospheric
conditions across the globe from observations of the current state, made from land; at
sea; in
the air, and from space.
In forecasting the weather, a Meteorologist must at least know something about the
existing weather condition over a large area before he can make a reliable forecast. The
accuracy of his forecast depends largely upon his knowledge of the prevailing weather
conditions over a very wide area.
The forecast decision is based on various forecasting tools. The basic tool of a weather
forecaster is the WEATHER MAP. The weather map depicts the distribution patterns of
atmospheric pressure, wind, temperature and humidity at the different levels of the
atmosphere.
• There are two types of the basic weather map namely, the surface map and the
upperair maps.
• There are five standard levels of the upper-air maps that are constructed twice daily
at
twelve-hourly interval.
• The surface maps are made four times daily at six-hourly intervals. On the surface
maps, the distribution patterns of rain or other forms of precipitation and cloudiness
can
also be delineated.
Surface weather map
Weather information is coded in a surface station model on surface weather maps. The
circle
at the center of the model is centered on the station location. The approximate time
that the
weather information was collected is shown in UTC with the date in the upper left
margin.
The surface weather map above is computer-analyzed for pressure by the addition of
isobars.
Also, the location of centers of relatively highest and lowest pressures are shown by H
and L,
respectively. In addition, the positions of frontal boundaries are displayed. The time of
the
frontal locations is given in the upper right margin. Finally, the position of radar echoes
from a
national network of NWS Doppler radars is overlain where echo intensity is shown by
the radar
reflectivity scale along the lower left margin.
RADAR INTENSITY SCALE
When the energy emitted by the radar antenna strikes particles of precipitation, such as
drops of water, snowflakes, ice pellets, or hail, a portion of that energy is reflected back
to the radar. The intensity of this energy is related to the number, size and type of the
precipitation particles.
Learning Goals:
Recognize weather map features including highs, lows, fronts, isobars, and use them to
infer
winds, clouds and bad weather.
Utilize forecast maps and barometers to anticipate how future weather will affect your
voyage.
Weather maps summarize weather info on a geographic frame of reference.
 Present weather - Maps that are created from current (or recent past) weather
observations are called Analysis Maps.
 Future weather - Maps produced by Numerical Weather Prediction (NWP) computer
codes for the future are Forecast Maps or progs (short for "prognosis").
Both maps can look similar to each other, so you need to find the Valid Time that is
printed on
each map to see if it is for the past, present, or future.
Forecasts further into the future are less and less accurate. For this reason, it is wise to
get
frequent updates to the weather analyses and forecasts to ensure that you have the
"freshest"
data.
Reading weather maps
The following example is for a weather analysis over the North Pacific Ocean. The first
image
below is the actual weather map, provided by the US NOAA Ocean Prediction Center
(OPC). The second image below is the same map for the same valid time, where I
annotated
features on the map. (Sorry, I cut off the "valid time" that was on the original map.)

Let's explore this map one step at a time. Focus on the the first map above, but use the
second map to help identify features.
1.High- and Low-pressure centers are indicated with H and L, respectively. On the
first map
above, the Lows are in red, and the Highs are in blue. Recall that Lows are associated
with
bad weather (clouds, wind, precipitation, fronts), and Highs with good weather (clear
skies,
light winds). The blue numbers with underlines indicate the central pressure of the low
or high
- - insert a decimal point in front of the last digit to get kPa.
Using the first map above, can you find 3 Lows on this map? Can you find 2 Highs on
this map?
2.Fronts are the curved lines with triangles (for cold front), semi-circles (for warm
front),
both on the same side of the line for occluded fronts, and both on opposite sides of the
line
for stationary fronts. On this map, cold fronts are blue, warm fronts are red, occluded
fronts
are purple, and stationary fronts switch between red and blue colors. Fronts usually
come out
of a Low like (curved) spokes of a wheel.
In summary, fronts are a focus of bad weather, strong winds, wind-direction shifts,
clouds, and
precipitation.
Cold fronts can have convective clouds (thunderstorms, squall lines, spotty heavy rain
showers) along them.
Warm fronts can have broad areas of strati form clouds with widespread areas of
drizzle and
light rain ahead of them.
Occluded fronts have bad weather similar to both cold and warm fronts.
Using the first map above, can you find 2 or more cold fronts? Can you find 2 or
more warm fronts? Can you find 1 occluded front? Can you find 1 stationary front?
3.Isobars connect lines of equal pressure. They are the curved lines shown in brown on
this
map. The unit of pressure is kiloPascals (kPa). The labels on isobars are abbreviated.
For
example:
 24 means 102.4 kPa
 16 means 101.6 kPa,
 04 means 100.4 kPa
 92 means 99.2 kPa
 68 means 96.8 kPa
Namely, insert a decimal point before the last number, and put "10" or "9" in front of
the
number (use whichever one gives a pressure closest to 100 kPa).
Why do we care about isobars? Because the wind blows almost parallel to the isobars.
The
closer neighboring isobars are to each other, the faster the wind speed. Wind speed and
direction is very important for sailing.
Using the first map above, can you find an isobar representing 100.8 kPa? Can you find
the 101.2 kPa isobar? How about the 98.0 kPa isobar?
4.Winds are not shown on this map (except at a few ships and islands). Instead, I
inferred
the winds from the isobars as discussed in item (3) above), and I drew these wind
directions
as black arrows on the second map above. In the Northern Hemisphere, winds go in a
direction such that low pressure is to the wind's left, and the winds are nearly parallel
to the
isobars, but the winds cross the isbars at a small angle (due to frictional drag against
the sea
surface). You can see in the second map above that my black arrows show directions
that are
consistent with the isobar directions. Also, I added "fast winds" where isobars are
closely
packed together, and "slow winds" where the isobars are spaced out.
Can you anticipate the wind direction in the upper right corner of the first map? How
about in the bottom right corner of the first map?
5. Warnings for marine weather hazards are abbreviated and enclosed in a small
blue
box. Warnings were discussed in the previous Learning Goal.
In the first map above, can you find the 2 locations with GALE warnings? How about
the location with Heavy Freezing Spray?
6.The first map also shows some other features, including developing fronts and Lows,
and
dying fronts. Also, the forecast movement of Low centers are shown with red
arrows. These are highlighted in the second map above. These features are important
for
sailors so that you don't accidentally plan your voyage into a location toward which bad
storms are moving, or where new storms are developing.
A barometer is another tool that sailors use to help them forecast the weather. A
barometer is
an instrument that measures air pressure. Changes in pressure are what generate
winds. A
dropping or falling barometer means an approaching low pressure system or front and
its
associated bad weather. A rising barometer means an approaching high pressure
system and
fair weather (but lighter or calm winds). Together with the weather forecast, a
barometer is a
great tool to help you to predict approaching weather.

WEATHER FRONT
A weather front is a transition zone between two different air masses at the Earth's
surface.
Each air mass has unique temperature and humidity characteristics. Often there is
turbulence at
a front, which is the borderline where two different air masses come together. The
turbulence
can cause clouds and storms.
Surface station model (sample station plot)
WEATHER
A weather symbol is plotted if at the time of observation, there is either precipitation
occurring
or a condition causing reduced visibility.
Below is a list of the most common weather symbols:
WIND
Wind is plotted in increments of 5 knots (kts), with the outer end of the symbol pointing
toward
the direction from which the wind is blowing. The wind speed is determined by adding
up the
total of flags, lines, and half-lines, each of which have the following individual values:
Flag: 50 kts
Line: 10 kts
Half-Line: 5 kts
If there is only a circle depicted over the station with no wind symbol present, the wind
is calm.
Below are some sample wind symbols:
PRESSURE
Sea-level pressure is plotted in tenths of millibars (mb), with the leading 10 or 9
omitted. For
reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample
conversions between plotted and complete sea-level pressure values:
410: 1041.0 mb (if nbr start from 0-4 the omitted nbr is 10, so 410 will read as
1041.0mb)
103: 1010.3 mb
987: 998.7 mb (if nbr start from 5-9 the omitted nbr is 9, so 987 will read as 998.7mb)
872: 987.2 mb
PRESSURE TREND
The pressure trend has two components, a number and symbol, to indicate how the sea-
level
pressure has changed during the past three hours. The number provides the 3-hour
change in
tenths of millibars, while the symbol provides a graphic illustration of how this change
occurred.
Below are the meanings of the pressure trend symbols:
SKY COVER
The amount that the circle at the center of the station plot is filled in reflects the
approximate
amount that the sky is covered with clouds. Below are the common cloud cover
depictions:
Sample Ship/Buoy Observation
TEMPERATURE
The current air temperature measured to the nearest whole degree Farenheit.
WEATHER
A weather symbol is plotted if at the time of observation, there is either precipitation
occurring
or a condition causing reduced visibility. Weather symbols: (same as in station plot
symbols)
DEW POINT
The current dew point temperature measured to the nearest whole degree Farenheit.
WIND
The same symbols as in station plot
PRESSURE
The same symbols as in station plot
PRESSURE TREND
The same symbols as in station plot
WATER TEMPERATURE
The current water temperature measured to the nearest whole degree Fahrenheit.
SWELL INFORMATION
The swell direction, period, and height are represented in the surface observations by a
6-digit
code. The first two digits represent the swell direction, the middle digits describe the
swell
period (in seconds), and the last two digits are the swell's height (in half meters). Below
are
two examples:
090703
09 -- The swell direction is from 90 degrees (i.e. it is coming from due east).
07 -- The period of the swell is 7 seconds.
03 -- The height of the swell is 3 half meters.
271006
27 -- The swell direction is from 270 degrees (due west).
10 -- The period is 10 seconds.
06 -- The height of the swell is 6 half meters.
WAVE INFORMATION
The period and height of waves are represented by a 5-digit code. The first digit will be
a
"1" for buoy observations and a "2" for ship observations. The second and third digits
describe the wave period (in seconds), and the final two digits give the wave height (in
half
meters). Below are two examples:
10603
1 -- A group identifier for a buoy.
06 -- The wave period is 6 seconds.
03 -- The wave height is 3 half meters.
20515
2 -- A group identifier for a ship observation.
05 -- The wave period is 5 seconds.
15 -- Wave height is 15 half meters.
SKY COVER
The same symbols as in station plot
STATION IDENTIFIER
The format of the station identifier depends on the observing platform.
Ship -- Typically 4 or 5 characters. If 5 characters, then the fifth will usually be a digit.
Buoy -- Whether drifting or stationary, a buoy will have a 5-digit identifier. The first
digit will
always be a "4".
C-MAN -- Stands for Coastal-Marine Automated Network, and are usually close to
coastal
areas. Their identifier will appear like a 5-character ship identifier, however the 4th
character will identify off which state the platform is located. For example, "SRST2" is a
C-MAN station located along the Texas coast (in this case near Sabine, TX).
Land -- Land stations will always be 3 characters, making them easily distinguishable
from ship,
buoy, and C-MAN observations.
https://www.wpc.ncep.noaa.gov/html/stationplot_buoy.shtml
1st Step: Observation
• Surface observations are made at least every three hours over land and sea.
• Land-based weather stations around the world and automatic stations observe the
atmospheric pressure, wind direction and speed, temperature of the air, humidity,
clouds, precipitation and visibility using standard weather instruments such as the
barometer, wind vane, anemometer, thermometer, psychrometer or hygrometer and
rain gauge.
• In addition to these, coastal weather stations, weather ships and ocean data buoy
observe the state of the sea by observing the height and period of wave.
• Upper air stations around the world also make observations at least every twelve
hours.
• The pressure, temperature, dew point temperature, wind direction and speed are
observed at selected levels in the atmosphere using radiosondes which record these
data by tracking helium-filled balloons attached to transmitters.
RADIOSONDE

The balloon has an Instrument packet that sends temperature, wind, and moisture data
back to
a computer.
These launches are imperative for the science of weather and the data they collect give
us a
snapshot of the state of the atmosphere all over the world.
Radiosondes are routinely launched twice a day from about 92 stations across the US
by the
National Weather Service. Of the 92, stations, 69 are located in the conterminous
United
States, 13 in Alaska, 9 in the Pacific, and 1 in Puerto Rico. NWS also supports the
operation of
10 other stations in the Caribbean. Worldwide, there are over 800 upper-air observation
stations and through international agreements data are exchanged between countries.
These launches are coordinated and launched a short time before 00z and 12z daily.
This
nearly simultaneous release gives us a basic picture of the state of the atmosphere at a
set time
two times a day.
Most radiosondes measure or calculate the following variables:
-Pressure
-Altitude
-Geographical position (Latitude/Longitude)
-Temperature
-Relative humidity
-Wind (both wind speed and wind direction)
-Cosmic ray readings at high altitude
The balloons used to carry the radiosondes are of course much larger than the “party
balloons”
we most often see. The balloons are made of rubber or latex and are filled with enough
hydrogen or helium to lift the radiosonde high into the atmosphere. These balloons
when
released are filled with about 1500 grams of helium and start out about 5 feet in
diameter. Of
course as the balloon ascends the atmospheric pressure decreases with height and the
balloon
expands. These balloons expand to a fairly impressive size and when they get to about
20-25
feet in diameter they burst and the radiosonde falls back to earth. To help minimize the
danger
to people and property, a parachute slows the descent of the instrument package as it
falls. The
flight vertically and horizontally can last in excess of two hours and reach heights of
over
115,000 feet and can travel more than 180 miles from the launch location.
Along its flight the radiosonde sends back by radio data to a computer at the launch
location to
be stored and combined with data from other launches to ingest into forecast models
we use
daily. Wind speed and direction aloft are also obtained by tracking the position of the
radiosonde in flight using GPS or a radio direction finding antenna. Observations where
winds
aloft are also obtained from radiosondes are called “rawinsonde” observations.
Data from these launches can be viewed in a graphical format on thermodynamic
diagrams
such as Skew-T log-P diagrams. http://weather.unisys.com/upper_air/skew/
Over a course of a year the National Weather Service launches about 75,000 weather
balloons
and few radiosondes are actually recovered. If you do happen to find one, be careful of
the
battery as it can leak and can cause skin and eye damage and could ruin a coffee table
fairly
quickly. The radiosondes themselves contain packaging to mail the unit back to NOAA
to be
refurbished and used again.
Another apparatus, the theodolite, is used in observing wind direction and speed also at
selected levels. In addition to these, commercial air planes observe the weather along
their
routes at specified times.
Theodolite
Diwata-1also known as PHL-Microsat-1 is a Philippine microsatellite launched to the
International Space Station (ISS) in March 23, 2016, and was deployed into orbit from
the ISS
in April 27, 2016. It is the first Philippine microsatellite and the first satellite built and
designed
by Filipinos.
2nd Step: Collection And Transmission Of Weather Data
Weather observations which are condensed into coded figures, symbols and numerals
are
transmitted via radiophone, teletype, facsimile machine or telephone to designated
collection
centers for further transmission to the central forecasting station at WFFC. Weather
satellite
pictures are transmitted to ground receiving stations while radar observations are
transmitted to
forecasting centers through a local communication system.
3rd Step: Plotting Of Weather Data
• Upon receipt of the coded messages, they are decoded and each set of observations is
plotted in symbols or numbers on weather charts over the respective areas or regions.
• Observations made over land and sea are plotted on the surface or mean sea level
charts which are prepared four times a day. Radiosonde, theodolite, aircraft and
satellite wind observations are plotted on upper level charts which are prepared twice
daily.
4th Step: Analysis Of Weather Maps, Satellite And Radar Imageries And Other
Data
SURFACE (MSL) CHART
The data plotted on this weather map are analyzed isobarically. This means the same
atmospheric pressure at different places are inter-connected with a line taking into
consideration the direction of the wind. Through this analysis, weather systems or the
so-called
centers of action such as high and low pressure areas, tropical cyclones, cold and warm
fronts,
intertropical convergence zone, can be located and delineated.
Using surface maps to predict the weather.
Weather Map Interpretation
What Are Upper Air Maps and How Are They Used?
The location of troughs and ridges can play an essential role in a region's weather.
Weather
observations above the ground are collected by weather balloons. Data from one a
single site
are plotted on a sounding, but an upper air chart can show information from multiple
observation sites.
Most upper air charts are plotted in pressure coordinates instead of height coordinates.
The
primary reason is that many meteorological concepts are more easily explained when
using
pressure. Using pressure coordinates shows the height of a pressure level, for example,
500
mb, above the observation stations. The height of a particular pressure level will
typically be
lower in colder environments and higher in warmer ones. When the upper atmosphere
is
observed, there are specific pressure levels that are always reported. These levels are
called
mandatory pressure levels and are the surface, 850 mb, 700 mb, 500 mb, and 300 mb
or 200
mb. Below is a look at a sample 500 mb chart.
500 mb/ 500 Hectopascal Chart Monday, April 30, 2018- 7 am CDT(Upper air map)
Generally, there is rising motion to the east of a trough, which could lead to the
development of
precipitation and thunderstorms if moisture and instability are present. To the west of a
trough,
sinking motion is usually observed.
The data plotted at a point on the map is called a station plot and is similar to one that
you might see on a surface map. However, there are a few differences between the
station
plot for a surface and an upper air map. Upper air maps report temperatures in Celsius.
The
number in the lower left is usually dewpoint depression, which is the difference
between the
temperature and the dewpoint. The height of the pressure surface is plotted in the top
right of
the station plot. Below is an example of how a station plot may look on an upper air
map.
Depending on which pressure level you're looking at, there are different rules for
interpreting
the height of a station plot. These rules are summarized below.
 850 mb: Add 1000 to the value in the height field. Example: A value of 419 becomes a
height of 1419 meters.
 700 mb: The leading number is either a 2 or 3, whichever brings the value closest to
3000. Example: 914 is 2,914 meters; 032 is 3,032 meters.
 500 mb: Add a zero to the end. Example: 548 becomes 5480 meters.
 300 mb & 200 mb: Add a 1 to the front and a 0 to the end Example: 065 is 10,650
meters
The two other features are the solid grey contours and the red dashed lines. The grey
lines are
height contours; similar to isobars on a surface map; height contours connect points of
equal
height. The red dashed lines are isotherms or lines of constant temperature. For
pressure
surfaces above 500 mb, you will sometimes see lines of constant wind speed, or isotachs
plotted.
While data on upper air maps are the same regardless of the pressure level, each level
is
typically used to learn something specific about the atmosphere. For instance, the 850
mb level
can be used to identify the low level jet, as well as fronts that may be difficult to pick
out on a
surface map. At 700 mb, moisture content can be inferred; low dew point depressions at
700
mb suggest the presence of very deep moisture from the surface to the 700 mb level.
The 500
mb level is usually considered to be the middle of the atmosphere approximately. At this
level,
the trough and ridge patterns tend to become more evident. Lastly, the 300 mb and 200
mb
levels are the jet stream levels and can give you a good idea of where the jet stream is
located.
In the warm seasons, the jet stream is closer to 200 mb whereas, in the cold season, it
is closer
to the 300 mb level.
Soundings and upper air charts are both essential tools for understanding the structure
of the
atmosphere above the ground. While soundings provide data for the upper levels over a
relatively small area, upper-level charts can give you a bigger picture of what's going
on in the
atmosphere. This broader scope can help you identify systems that could aid in the
development of precipitation and storms. Upper air charts play a vital role in
understanding
atmospheric structure.
Upper Level Charts Pt. 3 - Effects on Surface Features
Now we are ready to look at some of the interactions between features on surface and
upper
level charts.
On the surface map above you see centers of HIGH and LOW pressure. The surface low
pressure center, together with the cold and warm fronts, is a middle latitude storm.
Note how the counterclockwise winds spinning around the LOW move warm air
northward
(behind the warm front on the eastern side of the LOW) and cold air southward (behind
the
cold front on the western side of the LOW). Clockwise winds spinning around the HIGH
also
move warm and cold air. The surface winds are shown with thin brown arrows on the
surface
map.
Note the ridge and trough features on the upper level chart. We learned that warm air
is
found below an upper level ridge. Now you can begin to see where this warm air comes
from. Warm air is found west of the HIGH and to the east of the LOW. This is where the
two
ridges on the upper level chart are also found. You expect to find cold air below an
upper level
trough. This cold air is being moved into the middle of the US by the northerly winds
that are
found between the HIGH and the LOW.
Note the yellow X marked on the upper level chart directly above the surface LOW.
This is a
good location for a surface LOW to form, develop, and strengthen (strengthening means
the
pressure in the surface low will get even lower than it is now. This is also called
"deepening"). The reason for this is that the yellow X is a location where there is often
upper
level divergence. Similarly the pink X is where you often find upper level convergence.
This
could cause the pressure in the center of the surface high pressure to get even higher.
What is an upper air report? Surface data are reported by the National Weather Service
for
each hour. Upper air data are meteorological data that are measured in the vertical
layers of
the atmosphere. Upper air data are usually measured by twice daily radiosonde
soundings,
taken at 00 and 12Z (Greenwich time).
What is identified on a 500 MB map? In other words, the 500 mb height at any point on
the map tells us about the average air temperature in the vertical column of air
between the
ground surface and the 500 mb height plotted at that point. The height pattern tells us
where
the air is relatively cold and where it is relatively warm (see 500 mb side view.)
What are upper level winds? The flow of air around the globe is greatest in the higher
altitudes, or upper levels. Upper-level airflow occurs in wavelike currents that may exist
for
several days before dissipating. Upper-level wind speeds generally occur on the order
of tens
of meters…
How are upper air weather conditions measured? The radiosondes measure vertical
profiles of air temperature, relative humidity and pressure from the ground all the way
up to
about 19 miles. Temperature and relative humidity are measured electronically; a small
aneroid
barometer measures pressure.
What height is 500 hPa? In terms of height, 500 hPa is about 5,500 metres (18,000 feet)
above the ground. The top of that part of the atmosphere in which our weather is
formed is
known as the tropopause and is at about 11,000 metres (35,000 feet). The 500 hPa level
is,
thus, effectively half way up the atmosphere as we know it.
What is a constant pressure chart? constant-pressure chart. (Also called isobaric chart,
isobaric contour chart.) The synoptic chart for any constant-pressure surface, usually
containing
plotted data and analyses of the distribution of, for example, height of the surface,
wind,
temperature, and humidity.
What are weather maps used for? A weather map displays various meteorological
features
across a particular area at a particular point in time and has various symbols which all
have
specific meanings. Such maps have been in use since the mid-19th century and are used
for
research and weather forecasting purposes.
How many times per day on average are weather balloons launched for upper air
observations?
Twice a day, seven days a week, nearly 900 stations around the world (including at the
NWS
Weather Forecast Office in Green Bay) release weather balloons into the atmosphere to
obtain
upper air weather information.
What does a radiosonde measure? A radiosonde is a battery-powered telemetry
instrument
carried into the atmosphere usually by a weather balloon that measures various
atmospheric
parameters and transmits them by radio to a ground receiver. ... Radiosondes
measuring ozone
concentration are known as ozonesondes.
How are weather observations taken?
Observation methods
Basic weather observation instruments include thermometers, rain gauges, barometers,
and
anemometers (wind speed meters). Examples of more sophisticated equipment are wind
profilers, weather balloons (radiosondes), Doppler radar, and satellites.
What is a prognostic weather chart?
A prognostic chart is a map displaying the likely weather forecast for a future time.
Such charts generated by atmospheric models as output from numerical weather
prediction
and contain a variety of information such as temperature, wind, precipitation
and weather fronts.
What is an isobaric chart?
Isobaric Chart. The term 'Isobaric Chart' as it applies to the area of the weather can be
defined as ' A weather map representing conditions on a surface of equal atmospheric
pressure.
For example, a 500 mb chart will display conditions at the level of the atmosphere at
which the
atmospheric pressure is 500 mb.
What does it mean when the Isobar lines are close together?
The close spacing of pressure isobars would mean there is a steep pressure gradient of
air.
This is similar to the gradient lines on a contour map; the closer the lines are together,
the
steeper the gradient of the land.
What does it mean when isotherms are close together?
Isobars and isotherms are lines on weather maps which represent patterns of pressure
and
temperature, respectively. They show how temperature and pressure are changing over
space
and so help describe the large-scale weather patterns across a region in the map.
What conditions can you expect from closely spaced isobars?
Thus, closely spaced isobars mean strong winds; widely spaced isobars mean lighter
wind. From a pressure analysis, you can get a general idea of wind speed from contour
or isobar spacing. Because of uneven heating of the Earth, surface pressure is low in
warm
equatorial regions and high in cold polarregions.
What weather does a trough rings?
A trough is an elongated (extended) region of relatively low atmospheric pressure, often
associated with fronts. Troughs may be at the surface, or aloft, or both under various
conditions. Most troughs bring clouds, showers, and a wind shift, particularly following
the
passage of the trough.
What is the difference between a trough and a ridge?
Ridges and troughs are often mentioned on the weather forecast. A ridge is an
elongated
area of relatively high pressure extending from the center of a high-pressure region.
A trough is an elongated area of relatively low pressure extending from the center of a
region
of low pressure.
What causes a trough?
The trough axis is denoted by the purple line. ... This is the upper level extension of a
surface
low pressure center, which is why troughs are also called upper level lows. Notice the
relatively cold temperatures associated with the trough. This is caused by the
southward
transport of colder air in the lower troposphere.
What is the dew point mean?
The dew point is the temperature to which air must be cooled to become saturated with
water
vapor. When further cooled, the airborne water vapor will condense to form liquid
water (dew).
... The measurement of the dew point is related to humidity. A higher dew point
means there is more moisture in the air.
How do Meteorologist predict the weather?
Meteorologists are able to predict the changes in weather patterns by using several
different
tools. ... For example, weather balloons are special balloons that have a weather pack
on
them that measures temperature, air pressure, wind speed, and wind direction in all the
layers
of the troposphere.
What are Troughs and Ridges?
If you watch the weather on the nightly news, you may hear about troughs and ridges.
Have
you ever wondered what they are and why they are
important?
Troughs and ridges look like what you might expect; a trough is roughly U shaped. To
the east
of the trough, air will usually rise, allowing for the development of precipitation. The
wind
around a trough in the Northern Hemisphere will blow counterclockwise (northwest or
north to
the west of the trough and southwest or south to the east).
A ridge, on the other hand, looks like an upside down U. Fair weather is usually
associated
with ridges; air under a ridge sinks, which is not conducive for the development of
clouds and
precipitation. If you’re under a ridge during the summer, conditions are usually hot and
dry. In
the Northern Hemisphere, winds will blow clockwise around a high (northwesterly
northwest of
the ridge and southwesterly southwest of the ridge.
Broadly speaking, troughs and ridges are properties of the pressure field and they can
easily be
seen on a weather map. Troughs are found near low pressure areas while ridges are
found near
high pressure. Below is an example of what they tend to look like.
Troughs and ridges are important features in predicting the weather. They can tell you
whether rain or snow is on the way or if dry conditions are likely. So, pay attention next
time
the weather comes because knowing where you are in regards to a trough or ridge will
help
you understand your weather forecast.
https://blog.weatherops.com › what-are-upper-air-maps-and-how-are-they-us...
UPPER AIR CHARTS
The data plotted on this weather map are analyzed using streamline analysis. Lines are
drawn
to illustrate the flow of the wind. With this kind of analysis, anticyclones or high
pressure areas
and cyclones or low pressure areas can be delineated
Upper level map
Introduction to Upper Air Charts
One of the first things to always keep in mind is "weather is like the humidity, it's all
relative".
In most aspects of weather, observed values of pressure and temperature are not as
important
as the change in pressure or the change in temperature. In meteorology, we refer to the
"change in" as a gradient.
A sample 500 millibar upper air chart. The gradient is the largest where the brown lines
are
closest together.
Any time there is a rapid "change in" any particular weather element we will say the
"gradient"
is large. It is near these large gradients where the weather is most active.
A common example is found near cold fronts. The "change in" air pressure is typically
rapid
near a cold front and therefore the pressure "gradient" is large. The greater the
pressure
gradient is near a front the stronger the wind. This is just as true for the upper
atmosphere.
While the information a skew-t chart provides is invaluable, it will only tell us what is
happening
in the atmosphere at that location. To paint a complete picture of the atmosphere as a
whole
we need to view radiosonde data from many upper air observations.
We do this by creating constant pressure charts that let us see changes, and gradients,
in
atmospheric conditions across the country and around the world.
NUMERICAL WEATHER PREDICTION MODEL OUTPUT
The computer-plotted weather maps are analyzed manually so that weather systems
like
cyclones and anticyclones, troughs, etc. are located.
Numerical Weather Prediction:
Numerical Weather Prediction (NWP) uses the power of computers to make a forecast.
Complex
computer programs, also known as forecast models, run on supercomputers and
provide
predictions on many atmospheric variables such as temperature, pressure, wind, and
rainfall. A
forecaster examines how the features predicted by the computer will interact to
produce the
day's weather.
The NWP method is flawed in that the equations used by the models to simulate the
atmosphere are not precise. This leads to some error in the predictions. In addition, the
are
many gaps in the initial data since we do not receive many weather observations from
areas in
the mountains or over the ocean. If the initial state is not completely known, the
computer's
prediction of how that initial state will evolve will not be entirely accurate.
Despite these flaws, the NWP method is probably the best of the five discussed here at
forecasting the day-to-day weather changes. Very few people, however, have access to
the
computer data. In addition, the beginning forecaster does not have the knowledge to
interpret
the computer forecast, so the simpler forecasting methods, such as the trends or
analogue
method, are recommended for the beginner.
Numerical weather prediction (NWP) uses mathematical models of the atmosphere and
oceans to predict the weather based on current weather conditions. ... Postprocessing
techniques such as model output statistics (MOS) have been developed to improve
the handling of errors in numerical predictions.
There are two major types of weather models: Global models and
mesoscale/regional models.
Why Meteorologists Use Supercomputers
Every hour of every day, billions of weather observations are recorded
by weather satellites, weather balloons, ocean buoys, and surface weather stations
around
the world. Supercomputers provide a home for this tidal wave of weather data to be
collected and stored.
The CFS is one of the primary climate models used for forecasting planetary
scale weather conditions such as: El Nino, Madden Julian Oscillations (MJO), and
monsoons.
Explanation: A type of computer that is used for forecasting weather is entitled as
Supercomputers.
Meteorologists rely on data from satellites, ships, airplanes, weather stations and
buoys, and
devices dropped from airplanes or weather balloons. Climatologists and meteorologists
utilize
two basic types of forecasting: deterministic and probabilistic, both of which have
multiple
subsets.
A time series analysis is the most accurate way to create forecasts for different time
periods.
The North American Mesoscale Model (NAM) refers to a
numerical weather prediction model run by National Centers for Environmental
Prediction for
short-term weather forecasting.
Generally speaking, the European model has produced the most
accurate global weather forecasts.
ECMWF Model Description
The European Medium Range Forecast Model is considered one of the premiere global
forecasting model for the mid-latitudes. In 2006, the ECMWF made improvements that
resulted in accurate hurricane forecasting. The model is run twice a day at 0z and 12z.
Numerical Weather Prediction – A Real-Life Application at the Intersection
of Mathematics and Meteorology. In the daily operation of weather forecasts, powerful
supercomputers are used to predict the weather by solving mathematical equations that
model the atmosphere and oceans
The Short Answer: A seven-day forecast can accurately predict the weather about 80
percent of the time and a five-day forecast can accurately predict the weather
approximately
90 percent of the time. ... Meteorologists use computer programs called weather
models to
make forecasts.
Meteorologists use a variety of tools to help them gather information about weather
and
climate. Some more familiar ones are thermometers which measure air temperature,
anemometers which gauge wind speeds, and barometers which provide information on
air
pressure.
Meteorologists also use satellites to observe cloud patterns around the world, and radar
is
used to measure precipitation. All of this data is then plugged into super computers,
which
use numerical forecast equations to create forecast models of the atmosphere.
... Model Output Statistic (MOS) data.
A supercomputer that helps meteorologists to predict the weather. The computer
weather
model then takes this information about the current state of the atmosphere and runs it
through physics equations that predict how the weather changes over time.
Weather forecasting is the application of science and technology to predict the
conditions of
the atmosphere for a given location and time. ... Hence, forecasts become less accurate
as the
difference between current time and the time for which the forecast is being made (the
range
of the forecast) increases.
Weather is the combination of four factors––temperature, wind, precipitation, and
sunlight
and clouds––that occur at a given place and time.
There are four types of weather observations: surface, upper air, radar, and satellite.
Surface aviation weather observations (METARs) are a compilation of elements of the
current weather at individual ground stations across the United States.
analog method. A method of forecasting that involves searching historical
meteorological
records for previous events or flow patterns similar to the current situation, then
making a
prediction based on those past events or patterns.
Forecasts that use computers are called digital forecasts. ... Analog Forecasts Analog
forecasting involves comparing current weather patterns to patterns that took place in
the past. The assumption is made that future weather will behave in a similar fashion as
what
took place in the past.
In statistics, the accuracy of forecast is the degree of closeness of the statement of
quantity
to that quantity's actual (true) value. The actual value usually cannot be measured at
the time
the forecast is made because the statement concerns the future..
The vaunted European model did not have the best predictions for Hurricane Florence,
as
many meteorologists suggested. The American Global Forecast System (GFS) model
was
actually the most accurate, according to a National Weather Service analysis
of model performance.
Although many factors combine to influence weather, the four main ones are solar
radiation,
the amount of which changes with Earth's tilt, orbital distance from the sun and
latitude,
temperature, air pressure and the abundance of water.
Weather is a complex phenomenon which can vary over a short period of time and thus
is difficult to predict. It is easier to predict climate as it is the average weather pattern
taken over a long time.
There are six main components, or parts, of weather. They are temperature,
atmospheric
pressure, wind, humidity, precipitation, and cloudiness.
There are four types of weather observations: surface, upper air, radar, and satellite.
Surface aviation weather observations (METARs) are a compilation of elements of the
current weather at individual ground stations across the United States.
Forecasts that use computers are called digital forecasts. ...
Analog Forecasts Analog forecasting involves comparing current weather patterns to
patterns that took place in the past.
How do weather models work?
The foundation for models are mathematical equations based on physics that
characterize
how the air moves and heat and moisture are exchanged in the
atmosphere. Weather observations (pressure, wind, temperature and moisture)
obtained from
ground sensors and weather satellites are fed into these equations.
Accurate weather predictions are important for planning our day-to-day activities.
Farmers
need information to help them plan for the planting and harvesting of their crops. ...
Weather
forecasting helps us to make more informed daily decisions, and may even help keep us
out
of danger.
MONITOR WEATHER CHARTS
Plotted data on the cross-section, rainfall and 24-hour pressure change charts are
analyzed to
determine the movement of wind waves, rainfall distribution and the behavior of the
atmospheric pressure.
• Compare the current weather maps with the previous 24 - 72 hour weather maps level
by level to determine the development and movement of weather systems that may
affect the forecast area.
• Examine the latest weather satellite picture, noting the cloud formations in relation to
the weather systems on the current weather maps.
• Compare the latest weather satellite picture with the previous satellite pictures (up to
48
hours) noting the development and movement of weather systems that may affect the
country.
• Examine the latest computer output of the numerical weather prediction model noting
the 24-hour, 48-hour and 72-hour objective forecast of the weather systems that may
affect the forecast area.
• Analyze the latest radar reports and other minor forecasting tools.
5th Step: Formulation Of The Forecast
After the analysis of all available meteorological information/data has been completed,
the
preparation of forecasts follows.
The first and one of the preliminary steps is the determination as accurately as the data
permit,
of the location 24 hours hence of the different weather systems and the existing
weather over a
particular region.
In many cases a fairly satisfactory estimate of the direction and rate of movement may
be
made by simply measuring the movement during the last 12 or 24 hours and then
extrapolating, or extending, this movement into the future and hence what weather will
be
experienced in different areas in the immediate future.
How is weather forecast disseminated?
The forecasts are then aired in various radio stations by telephone or sent by telefax
machines
a few minutes after completion and are immediately sent to the weather stations
nationwide.
Copies are also furnished to different media outlets without delay.
Tools Used for Weather Forecasting
Weather forecasting use all kinds of tools to achieve this goal. We have instruments
called
barometers to measures atmospheric pressure, radar to locate and measures speed of
clouds,
thermometers to measure temperature, and computer models to process data
accumulated
from these instruments. However, to this day, humans with good experience can still do
a
better job at predicting the weather than computer models alone because humans are
often
involved in picking the most appropriate model for a situation.
DATA ACQUISITION
A forecast is basically predicting how the present state of the atmosphere will change
with time.
Needs lots of observation
Have global observations.
Procedures for collecting, taking the observations is determined by the World
Meteorological
Organizations
They’re sent to one of the three World Meteorological Centers
The World Meteorological Centers then forward the data to NCEP.
National Center for Environmental Prediction (Camp Spring, MD)
It is here that the data is analyzed
Maps, chart prepared
Computers models are run.
Most all information created at NCEP is sent to the NWS, public and private agencies.
FORECASTING TECHNIQUES
Persistence
• There are a variety of forecasting techniques
• Easiest one is called persistence – Tomorrows weather is same as todays weather.
• Most accurate for time scales of minutes – hours
• Not so accurate on time scale of a day or longer.
The Trend Technique
• If a phenomenon is in steady state, or is moving at constant speed, the trend
technique
can be used.
• Rate x time = distance
• So if distance traverse by cold front is known over a given time period, its position can
be extrapolated in time.
• More accurate on shorter time scales (minutes to hours)
• A short term forecast is called a “nowcast”
The Analogue Technique
Identify existing features on a weather chart that resemble those that occurred in the
past.
Use previous weather events to guide forecast -->>
“Pattern Recognition”
Useful method for longer-term forecasts (3days-months)
NWS issues:
6-10 day extended forecast
30 day outlooks
The “Climatology” Technique
A forecast that is based on “climatology” or average weather
Example:
Lets say the climatological records show that it rains only 1 day out of 100 during the
summer
months in LA.
Then, if you forecast “no rain” for any day in July and August, the probability you will be
wrong
is 1/100.
Therefore, the probability you will be right is about 99%
Note: precip forecasts are usually given as probabilities
Example: “there is a 60% chance of measurable precip at any random place in the
forecast
area.
Model Forecasts- Numerical Weather Prediction
• Predict the state of the atmosphere (e.g, pressure, temperature, precip, winds, etc.) in
time.
• The atmosphere and atmospheric processes are represented by mathematical
equations.
• The equations are solved on supercomputers and are initialized with observational
data.
• Most all of the forecast models are run at NCEP
• Models produce prognostic charts (progs) of the model output.
Forecast Types.
Based on forecast length of time:
• Nowcast:0-2 hr forecast
• Nowcast are created using the trend technique and monitoring observations
• Short-range forecast: 6-60 hours
• Generated with model output and forecaster experience/expertise
• Medium-Range forecast: 3- 8.5 day
• Generated with medium-range forecast models such as the GFS
• Long-Range Forecast:
• Also known as outlooks
Other Local factors to consider when forecasting
-Clouds during the day will decrease the maximum temperature expected
-With no clouds during the day, you will have higher max temperature
-Clouds at night will increase the minimum temperature
-With no clouds at night, you will have a low minimum temperature.
-With no snow cover, surface albedo is likely to be larger- surface will get warmer
With snow, surface stays colder during day since less short wave is absorbed.
Night:
Snow re emits long wave very well, so snow-covered surface will achieve a much lower
minimum temperature.
Forecasting with Surface Weather Charts:
Given that we know the weather associated with common features on a surface weather
charts,
for example:
Cold front-narrow band of showers
NE of warm front- light/moderate wide spread precipitation.
Warm sector- hot, humid
Etc.
If we can predict the movement of these feature based on its previous motion, we can
then
make a forecast with this information.
So, determining movement of weather systems is quite important for forecasting.
Forecasting Weather by Weather System Movement
If the movement of a weather system (e.g., cold front) is constant with time, then one
can
predict its position in time based on a past movement -->>
Hence Distance= Rate x Time
This only works if system has a constant speed with time.
If speed is variable, it won’t work.
Forecasting Weather System movement with pressure tendency.
Pressure tendency- The rate at which pressure is changing for a given period of time
(mb/hr)
Lines of constant pressure change are called isallobars
Lows will tend to move to region of largest negative pressure tendencies
Highs will tend to move to region of largest positive pressure tendencies.
R-Rising F- Falling
Forecasting “Rules of Thumb”
• On the 700 mb forecast chart, the 70% relative humidity line usually encloses
areas that are likely to have clouds.
• On the 700 mb forecast chart, the 90% relative humidity line often encloses
areas where precipitation is likely. If upward velocities are present, the chance of
measurable precipitation in enhanced.
• On the 850 mb forecast chart, snow is likely north of the -5 degrees Celsius
isotherm, whereas rain is likely south of this line.
• The 5400 1000-500 mb thickness line is also used during the cool season east of
the Rockies to forecast rain/snow.
• For the storm to intensify (deepen), an area of upper-level divergence must be
over the cyclonic storm. On a 500 mb forecast chart that shows vorticity, look for
a vorticity maximum (vort max) and remember that to the east of an area of
positive vorticity we usually find upper-level divergence, upward air motions, and
cyclonic storm motion
-Weather Wizard is a simple to use and affordable weather forecast system using e-mail
to
access high quality Met Office data, which can be displayed on the electronic chart.
-The forecast is received completely user-defined, by using the Forecast manager to
establish
the area you wish to be covered and the parameters to be included in the forecast
(pressure,
wind, significant height, wind sea and swell)
-Requested information is e-mailed to you and then automatically transferred from your
inbox
to be displayed on an electronic chart.
-Weather Wizard is built in to Tsunamis NaviGator or is available as a stand-alone
system.

Lesson – 5 Characteristics of Various Weather Systems

Tropical Revolving Storms (TRS)
WHAT IS TROPICAL REVOLVING STORMS?
Tropical Revolving Storm or TRS are intense tropical depressions which develops in
tropical
latitudes over large sea area. A tropical revolving storm may be defined as a roughly
circular
atmospheric vortex, originating in the tropics or sub tropics, where in the winds of gale
force
(34 knots or force 8) blow in spirally inwards (Anti-Clockwise in North Hemisphere and
Clockwise in South Hemisphere.
Within the circulation of a tropical storm the wind is often very violent and the seas are
high
and confused, considerable damage may be done even to large and well-built ships. The
dangers are prominent when ships are caught in restricted waters without sufficient
sea room
to maneuver. Nevertheless, TRS are a great danger to shipping regardless of where
they are
encountered and require a special study.
WMO maintains rotating lists of names which are appropriate for each Tropical Cyclone
basin. If
a cyclone is particularly deadly or costly, then its name is retired and replaced by
another
one. Experience shows that the use of short, distinctive given names in written as well
as
spoken communications is quicker and less subject to error than the older more
cumbersome
latitude-longitude identification methods. These advantages are especially important in
exchanging detailed storm information between hundreds of widely scattered stations,
coastal
bases, and ships at sea.
In the beginning, storms were named arbitrarily. An Atlantic storm that ripped off the
mast of a
boat named Antje became known as Antje's hurricane. Then the mid-1900's saw the
start of the
practice of using feminine names for storms.
In the pursuit of a more organized and efficient naming system, meteorologists later
decided to
identify storms using names from a list arranged alphabetically. Thus, a storm with a
name
which begins with A, like Anne, would be the first storm to occur in the year. Before the
end of
the 1900's, forecasters started using male names for those forming in the Southern
Hemisphere.
The only time that there is a change in the list is if a storm is so deadly or costly that
the future
use of its name on a different storm would be inappropriate for reasons of sensitivity. If
that
occurs, then at an annual meeting by the WMO Tropical Cyclone Committees (called
primarily to
discuss many other issues) the offending name is stricken from the list and another
name is
selected to replace it. Infamous storm names such as Mangkhut (Philippines, 2018),
Irma and
Maria (Caribbean, 2017), Haiyan (Philippines, 2013), Sandy (USA, 2012), Katrina (USA,
2005),
Mitch (Honduras, 1998) and Tracy (Darwin, 1974)
Procedure of naming tropical cyclones
There is a strict procedure to determine a list of tropical cyclone names in an ocean
basin(s) by
the Tropical Cyclone Regional Body responsible for that basin(s) at its annual/biennial
meeting.
There are five tropical cyclone regional bodies, i.e. ESCAP/WMO Typhoon Committee,
WMO/ESCAP Panel on Tropical Cyclones, RA I Tropical Cyclone Committee, RA IV
Hurricane
Committee, and RA V Tropical Cyclone Committee. For instance, Hurricane Committee
determines a pre-designated list of hurricane names for six years separately at its
annual
session.
The pre-designated list of hurricane names are proposed by its members that include
National
Meteorological and Hydrological Services in the North/Central America and the
Caribbean.
Naming procedures in other regions are almost the same as in the Caribbean. In
general,
tropical cyclones are named according to the rules at a regional level.
It is important to note that tropical cyclones/hurricanes are named neither after any
particular
person, nor with any preference in alphabetical sequence. The tropical
cyclone/hurricane names
selected are those that are familiar to the people in each region. Obviously, the main
purpose of
naming a tropical cyclone/hurricane is basically for people easily to understand and
remember
the tropical cyclone/hurricane in a region, thus to facilitate tropical cyclone/hurricane
disaster
risk awareness, preparedness, management and reduction.
If a storm is divided along the route, at which the storm is passing, then we get 2
parts, which are,
Navigable semicircle — It is the side of a tropical cyclone, which lies to the left of the
direction of movement of the storm in the Northern hemisphere (to the right in the
Southern
Hemisphere), where the winds are weaker and better for the navigation purpose,
although all
parts of TRS are more or less dangerous to mariners.
Dangerous semicircle— It is the side of a tropical cyclone, which lies to the right of
the
direction of movement of the storm in the Northern Hemisphere (to the left in the
Southern
Hemisphere), where the storm has the strongest winds and heavy seas.
Structure
1. The eye or vortex: A calm central area of lowest pressure, having a diameter
between 4
miles and 30 miles, the average being about 10 miles. It is a roughly circular area of
comparatively light winds and fair weather, available at the centre of a severe tropical
cyclone.
Weather in the eye is normally calm but the sea can be extremely violent. There is little
or no
precipitation and sometimes blue sky or stars can be seen. The eye is the region of
lowest
surface pressure than the surrounding environment. In severe cyclones, the eye usually
looks
like a circular hole in the central cloud mass.
2. The eye-wall: An inner ring of hurricane force winds having a width usually between
4
miles and 30 miles. The winds in the eye-wall blow in a perfectly circular path with a
speed as
high as 130 knots with occasional gusts up to 150 knots. The pressure gradient in the
eye-wall
is very steep and, therefore, the barograph would register a near vertical trend,
downward
before the eye and upward behind it, as shown in the figure. Eye wall consists of a
dense ring
of cloud and tall thunderstorms that produce heavy rains and usually the strongest
winds
(about force 6 or 7) at about circular path. Changes in the structure of the eye and eye
wall can
cause changes in the wind speed, which is an indicator of the storm’s intensity.
3. The Outer storm area: The area surrounding the eye-wall, having a diameter
between 50
miles and 800 miles, the average being about 500 miles. Winds in this region are strong
(about
force 6 or 7) and the pressure gradient is much less than in the eye-wall. Here angle of
indraft
of wind is about 45º and this gradually decreases to 0º in the eye wall. In this area, the
cirrus
cloud can be in the form of strands or filaments with aligned conditions and points
towards the
storm center. Here visibility is excellent, except in occasional shower’s areas.
Life cycle of a tropical cyclone
The complete life cycle of a tropical cyclone usually spans about 9 days but can be only
2 or 3
days or more than 20 days.
Formation
The formation of a tropical cyclone is dependent upon six favorable environmental
conditions
(described before), which are available in the Inter Tropical Convergence Zone.
Tropical
cyclones gain energy from latent heat, driven by significant thunderstorm activity and
condensation of moist air. In other words, tropical cyclone formation can be called as a
gigantic
vertical heat engine, which is also powered by earth’s gravity and rotation.
Premature Stage
In this stage, the area of convection continues and becomes more organized. Also
strengthening occurs simultaneously. The minimum surface pressure rapidly drops well
below
than normal level. Gale-force winds also develop with the strengthening pressure
gradient. The
circulation centre is well defined and subsequently, an eye may begin to form. Satellite
and
radar observations of the system show as the distinctive spiral banding pattern.
Premature
Stage of a tropical cyclone can cause devastating wind and storm surge effects upon
coastline,
but damage occurs usually within a small area.
Mature Stage
If the ocean and atmosphere environment continue to be favourable, the cyclone may
continue
to intensify to this stage. This is the severe cyclone stage, where the cyclone is most
dangerous. Approximately half of the cyclones can come up to this stage. During this
stage, the
cyclonic circulation and extent of the gales increase markedly. In satellite images, the
cloud
fields look highly organised and become more symmetrical, with a well-centered,
distinct round
eye. This stage remains for a day or so with maximum intensity unless the cyclone
remains in a
highly favourable environment

Decay Stage
At this stage, the warm core of TRS is destroyed, as the central pressure increases and
the
maximum surface winds weaken. Decay may occur very rapidly if the system moves into
an
unfavourable atmospheric or geographic environment. At this stage, the heavy or
medium rain
can be available.
Factors Associated with the decay of TRS
Decay of the TRS - Movement of these storms is controlled primarily by the movement
of the
upper warm core. They generally move westerly, then pole wards, then recurve easterly
into
higher latitudes. If they proceed over land, they lose intensity and degenerate into rain
depressions, although they may regenerate if they move over warm sea again.
Seasons of greatest frequency of TRS
North Atlantic – South of Lat. 35 N from north of Caribbean to the Gulf of Mexico;
occurs
mostly from June to November but also may occur any month; known as Hurricane.
Eastern North Pacific – occurs mostly from June through October but can occur any
month;
known as Hurricane.
Western North Pacific – Most of tropical revolving storms form in this region from
April
through December although it may occur in January to March.
Majority of these storms form east of the Philippines and move to the South China Sea
or up to
Japan after recurving; known as Typhoon. They are the largest and the strongest.
North Indian Ocean, Bay of Bengal and Arabian Sea – Occurs from February through
October; known as Cyclone.
South Indian Ocean – West of Longitude 100°E and south of latitude 10°S occurs
mostly
from December through March; known as Cyclone.
South Pacific and Australian Area – From longitude 105°E to 160°W between latitudes
50°S and 20°S occurs from December through April; known as Hurricane in the South
Pacific
and Willy-Willy in the Australian Area.
Tropical revolving storms do not occur between latitudes 5°N and 5°S due to the very
little effect of the Coriolis force and its absence at the equator.
In the stages of development of a tropical revolving storm the World Meteorological
Organization (WMO) has laid down the following nomenclature according to its
intensity:
Tropical Disturbances – The area of low pressure is surrounded maybe by one
closed isobar or none at all, and there is no strong wind.
Tropical Depression – There is a definite rotary circulation of the wind and one
or more closed isobars surround the low pressure area, and with wind speed less
than 34 knots.
Tropical Storm or Severe Tropical Storm – The pressure is lower than that in
tropical
depressions and wind speed reaches 34 to 63 knots.
Hurricane/Typhoon/Cyclone – The pressure at the center is much lower and
sustained
winds are 64 kts. or over. Typhoons in general cover a large area than hurricanes.
Recipe for a cyclone:
Pre-heat the ocean to at least 26ºC Get an area of low pressure Add lots of warm moist
unstable and disturbed air Mix well – using the Coriolis Force (between 5º-20ºNorth or
South of
the Equator) Cyclones need the Coriolis Force to generate the spin. There is no spin
created at
the equator, so that is why cyclones don’t form there (or cross the equator).
In the South Pacific, the cyclone season is over the Southern Hemisphere summer –
November
to April. With the greatest frequency in January – March.
In the Northeast Pacific the cyclone season is from June to November, but the
Northwest Pacific
has tropical cyclones all year round – with the most in early September and the least in
February & March
The North Atlantic has cyclones from June to November with the most occurring in
August &
September.
In the North Indian basin, their cyclone season is April to December – peaking in May
and
November.
Of course you should always be keeping an eye on the weather forecasts but some other
signs
that there may be a cyclone approaching include:
-a long low swell
- Extensive high cirrus clouds in the direction from where the storm is approaching
- A change of 3 hPa or more below the mean average pressure for the area
- A marked change in the direction of wind and speed
To find the direction of the storm – face the wind and the centre of the storm lies aprox
90º on your left hand side in SH, in your right in the NH.
A hurricane force wind is defined as any wind averaging 64 knots. These storms are
given
different categories depending on the wind speed.
Once a Tropical Revolving Storm has been identified it is given a name. There are
several
different Tropical Cyclone warning centers located around the world and they keep
their own
list of names in alphabetical order.
There are two warning centers in the South Pacific – one in Brisbane and one in Fiji, so
sometimes the names might not appear in alphabetical order. The storms are named to
make
them easier to identify one storm from another in weather reports.
They need the warm water to keep going, so if they move over land or head down in to
cooler
waters, they dissipate and become tropical storms or depressions. They are described
as
‘pressure valves’ allowing the heat from the ocean to be released and dispersed.
In the Southern Hemisphere, wind blows around the storm in a clockwise spiral flow
inward.
Their general track is usually in a South Westerly direction but it may change and then
head
South East.
Formation of tropical revolving storms
Tropical revolving storms start as a cloud mass on one side of the equator and develop
over
warm seas, with a temperature of around 80 degrees Fahrenheit. Moisture and warm
air rises,
reducing atmospheric pressure, leading to a depression in which the atmospheric
moisture
condenses to form large thunderclouds.
Cold air rushes in to fill the void left by the rising warm air. As the Earth rotates, this
air mass is
bent and spirals upwards with great force, with these swirling winds rotating with
increasing
speed forming a huge circle up to 2000 km across. As the storm builds up it begins to
move
while being sustained by a steady flow of warm, moist air.
Main Causes Rising warm air from seas in equatorial regions is the main cause of
tropical
revolving storms. This rising air condenses forming clouds while releasing massive
amounts of
heat. The combination of heat and moisture leads to the formation of many
thunderstorms from
which a tropical revolving storm can develop.
Impacts Extreme weather such as very high winds, thunder and lightning and torrential
rain is
associated with tropical revolving storms. These storms can cause significant damage to
infrastructure and loss of life. For instance, flooding commonly occurs following a
tropical
revolving storm, in particular when the storm crosses the coast, with low pressure near
the
center combining with strong onshore winds to produce a large increase in sea level,
called a
"storm surge."

FACTORS WHICH AFFECT THE MOVEMENT OF A TRS

Hurricane Movement
The movement of a hurricane from one location to another is known as hurricane
propagation.
In general, hurricanes are steered by global winds. The prevailing winds that surround
a
hurricane, also known as the environmental wind field, are what guide a hurricane
along its
path. The hurricane propagates in the direction of this wind field, which also factors
into the
system’s propagation speed. While each storm makes its own path, the movement of
every
hurricane is affected by a combination of factors, as described below.
In the tropics, where hurricanes form, easterly winds called the trade winds steer a
hurricane
towards the west. In the Atlantic basin, storms are carried by these trade winds from
the coast
of Africa, where they often develop (see Hurricane Genesis: Birth of a Hurricane),
westward
towards the Caribbean Sea and the North American coasts.
Embedded within the global winds are large-scale high and low-pressure systems. The
clockwise rotation (in the Northern Hemisphere) of air associated with high-pressure
systems
often cause hurricanes to stray from their initially east-to-west movement and curve
northward.
One such high-pressure system, often referred to as the Bermuda High (Azores
High) (depending on its location) or more generally as a subtropical ridge, often
dominates the
North Atlantic Ocean. Atlantic hurricanes typically propagate around the periphery of
the
subtropical ridge, riding along its strongest winds. If the high is positioned to the east,
then
hurricanes generally propagate northeastward around the high’s western edge into the
open
Atlantic Ocean without making landfall. However, if the high is positioned to the west
and
extends far enough to the south, storms are blocked from curving north and forced to
continue
west, putting a large bulls-eye on Florida, Cuba, and the Gulf of Mexico, as was the case
during
much of the 2004 and 2005 Atlantic hurricane seasons.
In addition to the steering flow by the environmental wind, a hurricane drifts
northwestward
(in the Northern Hemisphere) due to a process called beta drift, which arises because
the
strength of the Coriolis force increases with latitude for a given wind speed. The details
of
beta drift is beyond the scope of the discussion here, but the effect is summarized in the
following graphic. Since beta drift involves a hurricane’s ability to modify the
environmental
wind field, the impact of beta drift on the hurricane’s track changes if the hurricane’s
size
changes.
Air moving northward on the east side of a hurricane acquires
clockwise spin; air moving southward west of the storm acquires counterclockwise spin.
As a hurricane propagates northward out of the tropics, the environmental wind field
often
becomes weak, causing the hurricane to slow down, stall, or move erratically, especially
if the
hurricane is away from the influence of strong high or low pressure systems. Once a
hurricane
reaches further north and enters the mid-latitudes, the environmental wind field usually
becomes southwesterly or westerly, often around the western side of a high pressure
system
and east of a trough of low pressure, causing the hurricane to recurve to the right and
accelerate towards the north, northeast, or east. If a hurricane encounters the jet
stream while in the mid-latitudes, the storm may accelerate very quickly, allowing it to
reach
high latitudes, especially if it is travelling over a warm ocean current such as the Gulf
Stream.
Most of the time, however, land interaction, cold ocean water, or vertical wind
shear prevents a hurricane from surviving very far north of the tropics (see Hurricane
Decay:
Demise of a Hurricane).
While the environmental wind field and beta drift are generally the most important
factors
determining hurricane movement, other processes may also play a role. When vertical
wind
shear exists, the hurricane’s rotational wind field may tilt with height. By displacing
the cyclonic (counterclockwise in the Northern Hemisphere) circulation in the
lower troposphere downstream from the anticyclonic (clockwise in the Northern
Hemisphere) circulation in the upper troposphere, the vertical wind shear may allow
the lower
circulation to push the upper one and the upper circulation to push the lower one,
having a
combined effect of changing the track of the entire hurricane.
Wind shear pushes the anticyclone at storm top off to one side. The low level cyclone
and the
upper level anticyclone then pushes each other in one direction, in this case, toward the
north.
If a hurricane is in close proximity to another similarly-sized atmospheric circulation,
such as a
second hurricane, the two circulations may orbit cyclonically around a common point
between
them. This motion is known as the Fujiwhara effect.
Land interaction also may change the track of a hurricane, especially when the land is
mountainous. Mountains can disrupt the center of a hurricane’s circulation, which may
then
reform on the other side of the mountains away from the trajectory of the hurricane’s
track
prior to crossing the mountains.
MODIS satellite imagery of Typhoon Morakot before and after it moved over the high
mountainous terrain of Taiwan. (left) Typhoon Morakot approaching Taiwan with 148
km/h (92
mph) winds. (right) Morakot moving into inland China 2 days later. The typhoon had
become a
tropical storm, with 74 km/h (46 mph) winds, its structure greatly impacted by the high
mountains of Taiwan. Image credit: NASA.
Hurricane movements can be very unpredictable, sometimes performing loops, hairpin
turns,
and sharp curves. Forecasters track hurricane movements and predict where the
storms will
travel as well as when and where they will reach land. For more information on how
these
weather systems are observed over time, please see Hurricane Observation.
The factors which contribute to the intensity of a revolving storm
Instability. Tropical revolving storms usually form close to the Inter Tropical
Convergence
Zone (ITCZ) where there is marked instability.
Humidity. Storms mainly occur over the western parts of the tropical oceans where the
air has
had a long passage over the sea, or where air has crossed over from the other
hemisphere, and
has become saturated.
Latitude. For a given pressure gradient, the strength of the winds increases as the
storm
approaches the Equator. Temperature: Tropical revolving storms form over water
surfaces with
a water temperature of at least 27C.
Hurricane Measurement
Hurricanes are divided into five categories by wind speed using the Saffir-Simpson
hurricane
intensity scale. Destruction associated with major (category 3, 4 and 5) hurricanes
includes
damage to permanent homes, widespread coastal flooding, uprooting of trees, toppling
of
power lines. Anticipation of such damages prompts evacuation of residents from the
area of
expected landfall. Hurricane Camille in 1969 was the most recent category 5 hurricane
to make
landfall in the U.S., coming onshore along the Gulf Coast of Mississippi.
http://hurricanescience.net/science/science/hurricanemovement/
Saffir-Simpson Hurricane Intensity Scale
Category Wind Speed
km/hr (miles/hr)
Pressure
(millibars)
Storm Surge
meters (feet)
Damage
Description
1 119-154 (74-95) >980 1.2-1.5 (4-5) Minimal
2 155-178 (96-110) 965-979 1.6-2.4 (6-8) Moderate
3 179-210 (111-130) 945-964 2.5-3.6 (9-12) Extensive
4 211-250 (131-155) 920-944 3.7-5.4 (13-18) Extreme
5 >250 (>155) <920 > 5.4 (>18) Catastrophic

Tropical cyclone track forecasting

Involves predicting where a tropical cyclone is going to track over the next five days,
every 6 to
12 hours. The history of tropical cyclone track forecasting has evolved from a single-
station
approach to a comprehensive approach which uses a variety of meteorological tools and
methods to make predictions. The weather of a particular location can show signs of the
approaching tropical cyclone, such as increasing swell, increasing cloudiness, falling
barometric
pressure, increasing tides, squalls, and heavy rainfall.
The forces that affect tropical cyclone steering are the higher-latitude westerly's, the
subtropical
ridge, and the beta effect caused by changes of the coriolis force within fluids such as
the atmosphere. Accurate track predictions depend on determining the position and
strength
of high- and low-pressure areas, and predicting how those areas will migrate during the
life of a
tropical system. Computer forecast models are used to help determine this motion as
far out as
five to seven days in the future.
Four Factors that Can Strengthen Tropical Cyclones
- Sea surface temperatures warmer than 79 degrees Fahrenheit (26 degrees Celsius)
- Low vertical wind shear.
- Warm moist air.
- Ocean area along the projected storm track.
Four Factors that Can Weaken Tropical Cyclones
- Cooler Sea surface temperatures less than 79 degrees Fahrenheit (26 degrees Celsius)
- High vertical wind shear
- Dry air
- Land masses along the projected storm track

Reasons for naming the dangerous Circle

dangerous semicircle The side of a tropical cyclone to the right of the direction of
movement of
the storm in the Northern Hemisphere (to the left in the Southern Hemisphere), where
the
winds are stronger because the cyclone's translation speed and rotational wind field are
additive.
The opposite side is termed the navigable semicircle. This terminology originated in the
days of
sailing ships. It occurred naturally since 1) the dangerous semicircle of the storm has
the
strongest winds and heaviest seas; 2) a sailing ship on this side tends to be carried into
the
path of the storm; and 3) if the storm recurves, its center is likely to cross the course of
a ship
running before the wind.
The half of a cyclonic Storm in which the rotary and forward motions of the storm
reinforce
each other and the winds tend to blow a vessel into the storm track. In the Northern
Hemisphere this is to the right of the storm center (when facing the direction the storm
is
moving) and in the Southern Hemisphere it is to the left. The opposite is the LESS
DANGEROUS
or NAVIGABLE SEMICIRCLE.
Clouds and Precipitation
Clouds forming over mountain tops due to wind moving upslope and converging. In
order for
precipitation to form, particularly over a large area, several ingredients are necessary.
So, there
must be a process for the cloud water, or ice, to grow large enough to fall as
precipitation.
A cloud is a visible aggregate of tiny water droplets and/or ice crystals suspended in the
atmosphere and can exist in a variety of shapes and sizes. Some clouds are
accompanied by
precipitation; rain, snow, hail, sleet, even freezing rain. The purpose of this module is to
introduce a number of cloud classifications, different types of precipitation, and the
mechanisms
responsible for producing them.
Characteristics of a TRS, Size , Wind, Pressure, And Eye , Cloud, Precipitation
Sequence
-Cause
Warm (over 27C) moist air rises from the surface of the sea.
As it rises it meets cooler air and condenses to make clouds and rain.
This condensation releases huge amounts of energy, producing strong winds.
The winds are driven by the spin of the earth and go round and round.
As the earth rotates the winds are sucked violently upwards in a vortex which can be
1,000km
wide. Wind speeds can be as high as 200km per hour.
These storms are fueled by damp air when they reach land, dry air is being sucked up
and they
loose energy.
Origin, movement and life span
Tropical revolving storms travel from place of origin in a westward direction and
inclined more
and more towards the pole and then curve eastward approximately in latitudes 20°N or
S. The
position where its westward movement changes to eastward is called the “point of
recurvature”. Thus, in the northern hemisphere the general direction of movement is
roughly
west, northwest, north and finally northeast.
In the southern hemisphere it is west, southwest, south and finally southeast. After
reaching
temperate latitudes the storms tend to dissipate (disperse) or join up with extra-tropical
cyclones and lose its character as a tropical storm. The easterly wave gives the storm
its initial
westerly movement. However, some storms do not follow this pattern and move
erratically.
TRS originate in latitudes between 5° & 20° and travel between W and WNW in the NH
and
between W and WSW in the SH, at a speed of about 12 knots. Somewhere along their
track,
they curve away from the equator – curve to N and then recurve to NE in the NH; curve
to S
and then recurve to SE in the SH.
Terms used in connection with tropical revolving storms:
Storm Field – This is the region covered for the time being by the winds forming the
storm.
Track – The route over which a TRS is already passed.
Path – The predicted route, over which, there is a possibility of the TRS passing at near
future.
Vertex or cod-which is the westernmost point, of the TRS, when recurving takes place.
Vortex or Center or Eye – This is the central almost windless area within the ring of
hurricane force wind, and where the atmospheric pressure (barometric pressure) is
lowest. The
sky above is usually clear but the sea is confused and mountainous.
If the eye of the storm passes over the observer’s position, the winds suddenly weaken
to just a
breeze as the eye passes; the rain stops and the sky becomes clear that sunlight can be
seen in
the day, but confused and mountainous wave come from all sides, and the barometer
reaches
its lowest reading. When the eye has passed the wind resumes with full violence as
suddenly as
it stopped but from the opposite direction.
Right- Hand Semicircle – This refers to right side half of the storm field for an
observer
looking towards the path. In the northern hemisphere this is the dangerous semicircle”
and the
forward quadrant is called the “dangerous quadrant.”
Left- Hand Semicircle – This refers to left side half of the storm field for an observer
looking
toward the path. In the northern hemisphere this is the “navigable semicircle.”
In the southern hemisphere, the right- hand semicircle is the navigable semicircle, and
the left- hand semicircle is the dangerous semicircle.
Trough Line – This is the line through the center of the storm at right angles to the
path. It is
also the dividing line between falling (decreasing) and rising pressure.
Bar of the Storm – This term means the advancing edge of the storm field.
Angle of Indraft – This is the angle that the wind direction makes with isobars.
Typical cloud formations associated with tropical revolving storms are cirrus,
cirrostratus,
altostratus, stratocumulus and cumulonimbus and scuds.
The main source of energy that powers tropical storm is the latent heat that is released
during condensation of the water vapor in the ascending currents of tropical air mass.
Another example of the typical path of storm
Path of A TRS
The recurving is such that the storm travels around the oceanic high (which is situated
at about
30°N and 30°S in the middle of large oceans). After recurving, the speed of travel
increases to
about 15 to 20 knots. Sometimes, a TRS does not curve or recurve at all, but continues
on its
original path, crosses the coast and dissipates quickly thereafter due to friction and
lack of
moisture.
It is important to note that all TRSs do not follow such definite paths and speeds. In
their initial
stages, occasional storms have remained practically stationary or made small loops for
as long
as four days.
Determining the semicircle which the vessel is in
First determine the true wind direction. If the wind is veering (shifting to the right)
the vessel is in the right- hand semicircle; if the wind is backing (shifting to the left) the
vessel
is in the left- hand semicircle.
The rule is true in both hemispheres so that by means of this you will know whether
your vessel
is in the dangerous semicircle or in the navigable semicircle, the vessel is in the direct
path of
the storm, or is going at the same speed and direction as the storm.
If you are not sure of the storm’s movement relative to the vessel, you should heave –
to (stop the ship) until this is ascertained. The storm’s movement must be continuously
checked
either by radio weather reports or by means of actual observation as outlined in the
above
paragraphs.
In the northern hemisphere (NH), conditions on the right-hand side of storms are more
severe
than those on their left-hand sides. For that reason, in NH, RHSC is called the
“dangerous
semicircle” and LHSC is called the “navigable semicircle”.
Navigable semicircle — It is the side of a tropical cyclone, which lies to the left of the
direction of movement of the storm in the Northern hemisphere (to the right in the
Southern
Hemisphere), where the winds are weaker and better for the navigation purpose,
although all
parts of TRS are more or less dangerous to mariners.
Dangerous semicircle— It is the side of a tropical cyclone, which lies to the right of
the
direction of movement of the storm in the Northern Hemisphere (to the left in the
Southern
Hemisphere), where the storm has the strongest winds and heavy seas.
In the dangerous semicircle the winds are stronger than in the navigable semicircle,
and the
rotary direction is more inclined towards the center. A ship caught in this area is bound
to be
driven into the center of the storm if not correctly maneuvered.
Signs which give warning of the Approach of the TRS
1. Warning and alerting messages
The Radio/Telex/NAVTEX and all other means at hand should be set on the right
frequencies
and monitored closely, for they broadcast comprehensive warnings with respect to
known
storms. Refer to the respective ALRS Volumes for more data and frequencies of radio
stations in
the vicinity. The Telex, although barely used, is also a very important tool that is high
on
accuracy.
2. Swell
When there is no sight of intervening land, the sea might generate swell within a TRS,
indicating an early warning of the formation of the same. Normally, the swell
approaches from
the direction of the storm.
3. Atmospheric Pressure
Monitor the barometer closely in case you are suspicious of a brewing storm. If the
corrected
barometer reading falls below 3 mb or more for the mean reading for that time of the
year
(check the Sailing Directions for accurate information of pressure readings), you can
expect a
(Tropical Revolving Storm) TRS. Note that the barometer used must be corrected for
latitude,
height, temperature etc. to achieve maximum possible accuracy and efficiency.
4. Wind
Wind direction and speed is generally fairly constant in the tropics. Variation from the
normal
direction for the area and season, and increasing wind speed, are indications of the
approach of
a Tropical Revolving Storm, i.e., an appreciable change in the direction or strength of
the wind
indicates a Tropical Revolving Storm (TRS) in vicinity.
5. Clouds
A very candid and colorful sky at sunrise and sunset may be a sign of a brewing TRS.
Presence
of cirrus clouds is visible at a considerable distance of 300 to 600 miles from the TRS
and as
you approach the TRS, the clouds get lower and cover a bigger area (altostratus).
Generally
followed by cumulus clouds as you get closer to the Tropical Revolving Storm (TRS).
6. Visibility
Although it might sound like an oxymoron, exceptionally good visibility exists when a
TRS is
lurking in proximity!
7. Radar
The radar gives a fair warning of a Tropical Revolving Storm (TRS) about 100 miles
prior to
approaching the TRS. The eye may sometimes be seen on the screen. An area of rain
surrounds the eye (the eye of the storm is the storm center) causing appreciable clutter
on the
radar screen
Remember that though the signs might be visible on the radar, by the time it does
become visible on the radar, the vessel is probably already experiencing high seas and
gale
force winds and rough weather overall. Action is to be taken before such a situation
arises.
A general sequence of events that could occur during the development of a Category
2 hurricanes (wind speed 96-110 mph) approaching a coastal area.
96 hours before landfall
 At first there aren’t any apparent signs of a storm. The barometer is steady, winds are
light and variable, and fair-weather cumulus clouds appear.
72 ours
 Little has changed, except that the swell on the ocean surface has increased to about
six
feet and the waves come in every nine seconds. This means that the storm, far over the
horizon, is approaching.
48 hours
 The sky is now clear of clouds, the barometer is steady, and the wind is almost calm.
 The swell is now about nine feet and coming in every eight seconds.
36 hours
 The first signs of the storm appear. The barometer is falling slightly, the wind is
around
11 mph, and the ocean swell is about 13 feet and coming in seven seconds apart. On
the horizon, a large mass of white cirrus clouds appear.
 As the veil of clouds approaches, it covers more of the horizon.
 A hurricane watch is issued, and areas with long evacuation times are given the order
to
begin.
30 hours
 The sky is covered by a high overcast. The barometer is falling at .1 millibar per hour;
winds pick up to about 23 mph.
 The ocean swell, coming in five seconds apart, is beginning to be obscured by
winddriven waves, and small whitecaps begin to appear on the ocean surface.
24 hours
 Small low clouds appear overhead. The barometer is falling by .2 millibars per hour,
the
wind picks up to 34 mph. The wind driven waves are covered in whitecaps, and streaks
of foam begin to ride over the surface. Evacuations should be completed and final
preparations made by this time. A hurricane warning is issued, and people living in low
lying areas and in mobile homes are ordered to evacuate.
18 hours
 The low clouds are thicker and bring driving rain squalls with gusty winds. The
barometer is steadily falling at half a millibar per hour and the winds are whistling by at
46 mph. It is hard to stand against the wind.
12 hours
 The rain squalls are more frequent and the winds don’t diminish after they depart.
The
cloud ceiling is getting lower, and the barometer is falling at 1 millibar per hour. The
wind is howling at hurricane force at 74 mph. The sea advances with every storm wave
that crashes ashore, and foam patches.
6 hours
 The rain is constant and the 92 mph wind drives it horizontally. The barometer is
falling
1.5 millibar per hour, and the storm surge has advanced above the high tide mark.
Thesea surface a whitish mass of spray. It is impossible to stand upright outside without
bracing yourself.
1 hour
 The rain becomes heavier. Low areas inland become flooded. The winds are at 104
mph, and the barometer is falling at 2 millibar per hour. The sea is white with foam and
streaks. The storm surge has covered coastal roads and 16 foot waves crash into
buildings near the shore.
AFTER THE STORM
1 hour after landfall
 The sky darkens and the winds and rain return just as heavy as they were before the
eye. The storm surge begins a slow retreat, but waves continue to crash ashore. The
barometer is rising at 2 millibar per hour, and the winds top out at 104 mph.
6 hours
 The flooding rains continue, but the winds have diminished to 92 mph. The storm
surge
is retreating and pulling inland debris out to sea.
12 hours
 The rain now comes in squalls, and the winds begin to diminish after each squall
passes.
The cloud ceiling is rising, as is the barometer at 1 millibar per hour. The wind is still
howling at near hurricane force at 69 mph, and the ocean is covered with streaks and
foam patches. The sea level returns to the high tide mark.
24 hours
 The clouds break into smaller fragments and the high overcast is seen again. The
barometer is rising by .2 millibar per hour, the wind falls to 34 mph. The surge has fully
retreated from land, but the ocean surface is still covered by small whitecaps and large
waves.
36 hours
 The overcast has broken and the large mass of white cirrus clouds disappears over
the
horizon. The barometer is rising slightly, the winds are a steady 11 mph.
Actions in TRS, at port
Double the moorings.
Keep Engine standby.
All persons to be onboard.
Keep all LSA at the standby position.
Rig lifeline at fore and aft.
No slack tanks.
All hatches should be securely battened down.
All derricks should be lowered and secured.
Adequate fenders should be placed between the ship and the jetty.
Actions in TRS, at anchorage
 If possible, first try to go to sea at safe distance with plenty sea room and sufficient
depth of water or shift to a safe anchorage with enough shelter. Otherwise, do the
following:
Drop both anchors with several cables in water.
Keep Engine standby.
All persons to be onboard.
Keep all LSA at the standby position.
Rig lifeline at fore and aft.
No slack tanks.
All hatches should be securely battened down.
All derricks should be lowered and secured.
All bridge equipment (including Radar, fog-horn) and navigational lights (including
emergency
navigational lights) should be in standby mode.
Actions in TRS, At sea
If the vessel is in the dangerous quadrant:
 Proceed as fast as practicable with the wind 1 to 4 points on the stbd bow in NH (port
bow in SH) – 1 point for slow vessels (less than 12 knots) and 4 points for fast vessels
(more than 12 knots) altering course as the wind veers in NH (backs in SH).
 This action should be kept up until the pressure rises back to normal i.e. until the
vessel
is outside the outer storm area. If there is insufficient sea room, the vessel should heave
to with the wind on the stbd bow (port bow in SH) until the storm passes over.
If the vessel is in the path of the storm or if in the navigable semi-circle:
 Proceed as fast as practicable with the wind about 4 points on the stbd quarter in NH
(port quarter in SH), altering course as the wind backs in NH (veers in SH). This action
should be kept up until the pressure rises back to normal i.e. until the vessel is outside
the outer storm area.
Determining the approximate Bearing of approaching TRS
Locating the center of the storm
To avoid the full fury of a tropical storm early determination of its location and direction
of travel relative to the vessel’s position is essential. The Maritime Weather Broadcast
(weather
report broadcast by shore stations) provides information about the storm’s location,
direction
and speed of movement, wind force, state of sea, etc. printouts from the facsimile
machine also
give this information. Although these are reliable sources, the information obtained
should,
however, be rechecked by actual observation of the weather made on board the ship in
order to
enable the vessel to be maneuvered to the best advantage. When the center is within
radar
range, it might be located by radar. To locate the storm center by actual observation,
employ
the Buys Ballot’s Law, that is in the northern hemisphere face the wind and the center
is 10 to
12 points of the compass to your right when it is about 200 miles away and 8 points to
your
right when already near your position. In the southern hemisphere it is to your left
when you
face the wind and same points of the compass as above.
Some of the important characteristics of a Tropical Revolving Storm (TRS) that are:
• They appear smaller size than temperate depressions
• They form near the Inter Tropical Convergence Zone, a zone of instability
• They have nearly circular isobars
• No fronts occur (a front is the boundary between two air masses, often distorted by
warmer air bulging into the colder air)
• They result in a very steep pressure gradient
• They have great intensity
Actions to be taken when in the vicinity of a Tropical Revolving Storm
1)As required by SOLAS transmit by radio a priority message to the nearest coastal
radio station
giving the necessary information about the storm as observed by you.
2)Place the ship in a position of safety by doing the following:
a) Determine the bearing of the center and its distance from the ship.
b) Determine the semicircle which the ship is in.
c) Plot the probable path, and draw a probable danger area for a two-day’s forecast
movement.
d) Maneuver the ship accordingly.
In the absence of reliable sources, the bearing of the center and its distance from the
ship could be fairly estimated from the barometric pressure, true wind direction and
force and
by means of the Buys Ballots Law as follows:
1. In the northern hemisphere – When the barometer has fallen 5 mb below the normal
for that
place, face the wind (true wind) and the bearing of the center is about 12 points of the
compass to your right and the distance is probably not more than 200 miles away if the
wind
force is about 6; if the wind force is about 8 the center is probably within 100 miles. If
the
barometer has fallen 10 mb from the normal, the center is about 10 points of the
compass to
your right and the wind should be increasing in force as the storm is coming closer;
when it has
fallen 20mb from normal the center is about 8 points of the compass to your right and
already
close to your position so that the wind force would now approach hurricane force.
2. In the southern hemisphere – the procedure is the same as in the northern
hemisphere
except that when you face the wind the center is to your left.
3. In the northern hemisphere – When the barometer has fallen 5 mb below the normal
for that
place, face the wind (true wind) and the bearing of the center is about 12 points of the
compass to your right and the distance is probably not more than 200 miles away if the
wind
force is about 6; if the wind force is about 8 the center is probably within 100 miles. If
the
barometer has fallen 10 mb from the normal, the center is about 10 points of the
compass to
your right and the wind should be increasing in force as the storm is coming closer;
when it has
fallen 20mb from normal the center is about 8 points of the compass to your right and
already
close to your position so that the wind force would now approach hurricane force.
4. In the southern hemisphere – the procedure is the same as in the northern
hemisphere
except that when you face the wind the center is to your left.
It is worth noting that storms on the western side of the South Indian Ocean have very
large
angle of indraft so that in some areas of the storm field the wind blows at right angles
to the
isobars towards the storm center. In such cases estimation of the bearing endeavors
you to get
information from radio broadcast storm warnings and/or facsimile printouts. If the SE
trade
wind is increasing in force and the barometer is falling it means that the ship is on the
path or
in the dangerous semicircle (most probably in the dangerous quadrant) of the storm.
Correct avoidance procedure of a TRS
•1-2-3 Rule onboard
•Plot the current and forecast 24 Hour storm position and forecast radius of 34 knots
wind.
•Using Compass extend the radius of the forecast 24 hours 34 knots wind area by 100
nm.
•Draw tangents relative to the direction of the storm from the 34 knots radius of the
current
position of storm to the outermost radius at the 24 hour forecast position. The area
between
this is the Danger Area and is to be avoided.
•Use the same procedure for 48 & 72 hours forecast position, however to draw the
outermost
circle use 200 nm and 300 nm as radius respectively.
Mariner’s 1-2-3 rule, also known as the Danger Rule, is a guideline mariner should
follow to
avoid a tropical storm or hurricane’s path. In order to help account for the inherent
errors in
hurricane forecasting, a few guidelines should be used by the mariner in order to limit
the
potential of a close encounter between ship and storm.
34 Knots Rule 34 Knots is chosen as the critical value because as wind speed increases
to this
speed, sea state development approaches critical levels resulting in decreasing ship
maneuverability. Also, the state of the sea outside of the radius of 34 KT winds can also
be
significant enough as to limit course and speed options available to the mariner and
must also
be considered when avoiding hurricanes.
1-2-3 Rule This is the single most important aid in accounting for hurricane forecast
tract
errors (FTE). Understanding and use of this rule should be mandatory for any vessel
navigating
near a hurricane. The rule is derived from the latest 10-year average FTE associated
with
hurricanes in North Atlantic. While this rule was derived in the North Atlantic, it is a
good
technique to use in any tropical cyclone basin.
The 1-2-3 rule establishes a minimum recommended distance to maintain from a
hurricane in
the Atlantic, as it was derived from Atlantic tropical cyclone date. Mariners in the
Pacific can
use this rule as a guide. Larger buffer zones should be established in situations with
higher
forecast uncertainly, limited crew experience, decreased vessel handling, or other
factors set by
the vessel master.
The rule does not account for sudden and rapid intensification of hurricanes that could
result in
an outward expansion of the 34 KT wind field. Also, the rule does not account for the
typical
expansion of the wind field as a system transitions from hurricane to extratropical gale/
storm.
MESSAGES REQUIRED TO BE SENT IN ACCORDANCE WITH THE REQUIREMENTS
OF
SOLAS, WHEN ENCOUNTERED, OR SUSPECTED TO BE IN THE VICINITY OF A TRS
According to SOLAS Chapter V – 1/7/02 Regulation 5 - Meteorological services
and
warnings:
Contracting Governments undertake to carry out, in cooperation, the following
meteorological
arrangements about TRS:
To warn ships of gales, storms and tropical cyclones by the issue of information in text
and, as
far as practicable graphic form, using the appropriate shore-based facilities for
terrestrial and
space radio communications services.
When in the vicinity of a tropical cyclone, or of a suspected tropical cyclone, ships
should be
encouraged to take and transmit their observations at more frequent intervals
whenever
practicable, bearing in mind navigational preoccupations of ships' officers during storm
conditions.
REGULATION 32 - Information required in danger messages
The following information is required in danger messages:
Tropical Storms:
• A statement that a tropical cyclone has been encountered. This obligation should be
interpreted in a broad spirit, and information transmitted whenever the master has
good
reason to believe that a tropical cyclone is developing or exists in the neighborhood.
• Time, date (Universal Co-ordinated Time) and position of ship when the observation
was
taken.
As much of the following information as is practicable should be included in the
message:
Barometric pressure, preferably corrected (stating millibars, millimeters, or inches, and
whether
corrected of uncorrected); barometric tendency (the change in barometric pressure
during the
past three hours); true wind direction; wind force (Beaufort scale); state of the sea
(smooth,
moderate, rough, high); swell (slight, moderate, heavy) and the true direction from
which it
comes. Period or length of swell (short, average, long) would also be of value; true
course and
speed of ship.
When a master has reported a tropical cyclone or other dangerous storm, it is desirable
but not
obligatory, that further observations be made and transmitted hourly, if practicable, but
in any
case at intervals of not more than 3 hours, so long as the ship remains under the
influence of
the storm.
Example:
Tropical cyclone
TTT STORM. 0030 UTC. AUGUST 18. 2004 N, 11354 E. BAROMETER CORRECTED 994
MILLIBARS, TENDENCY DOWN 6 MILLIBARS. WIND NW, FORCE 9, HEAVY
SQUALLS. HEAVY
EASTERLY SWELL. COURSE 067, 5 KNOTS.
MESSAGES REQUIRED TO BE SENT IN ACCORDANCE WITH THE REQUIREMETS OF
SOLAS, WHEN THE WIND OF OR ABOVE STORM FORCE 10 IS ENCOUNTERED
WHICH
HAS NOT PREVIOUSLY BEEN REPORTED.
Winds of force 10 or above on the Beaufort scale for which no storm warning has been
received. This is intended to deal with storms other than the tropical cyclones; when
such a
storm is encountered, the message should contain similar information to that listed
under the
paragraph but excluding the details concerning sea and swell.
Example:
TTT STORM. WIND FORCE 11, NO STORM WARNING RECEIVED. 0300 UTC. MAY 4.
4830 N, 30
W. BAROMETER CORRECTED 983 MILLIBARS, TENDENCY DOWN 4 MILLIBARS.
WIND SW,
FORCE 11 VEERING. COURSE 260, 6 KNOTS.
Sub-freezing air temperatures associated with gale force winds causing severe ice
accretion on
superstructures:
Sea temperature (if practicable).
Air temperature.
Wind force and direction.
Time and date (Universal Co-ordinated Time).

Lesson - 6 The main types of floating ice, their origins and

movements
Ice Movement
Ice movement can cause shoreline erosion, damaging sensitive wetland areas, and
waterfront
habitat. Water quality can be affected by ice scouring that mixes sediment into the
water
column. Wildlife, particularly deer, travel on the ice. Unusual ice movement and vessel
tracks
which create open water have resulted in deer mortality as the animals are unable to
scramble
onto solid ice once they fall into the water.
Types of flow:
Internal Deformation, Rotational, Extensional and Basal Sliding, warm and cold
based glaciers.
INTERNAL DEFORMATION
These glaciers are frozen to the bed and therefore only move 1-2cm a day. The ice
crystals within the glacier orientate themselves in the direction of ice movement. This
allows
ice crystals to slide past one another. Where the ice movement is fast enough crevasses
may
develop (this process could also occur in warm based glaciers).
All glaciers start with snowfall that accumulates faster than it melts. As the years pass,
layers of snow pile up, compressing the layers below into dense ice. This process
continues
until the mountain of ice becomes very heavy. It starts to move when the weight
becomes too
heavy to maintain the glacier's shape.
ROTATIONAL MOVEMENT OF ICE
The Earth rotates about its axis once a day, but it does not do so uniformly. Instead, the
rate of rotation varies by up to a millisecond per day. Like a spinning ice skater whose
speed of
rotation increases as the skater’s arms are brought closer to their body, the speed of
the Earth’s
rotation will increase if its mass is brought closer to its axis of rotation.
Melting land ice, like mountain glaciers and the Greenland and Antarctic ice sheets, will
change the Earth’s rotation only if the melt water flows into the oceans. If the melt
water
remains close to its source (by being trapped in a glacier lake, for example), then there
is no
net movement of mass away from the glacier or ice sheet, and the Earth’s rotation
won’t
change. But if the melt water flows into the oceans and is dispersed, then there is a net
movement of mass and the Earth’s rotation will change.
Melting sea ice, such as the Arctic ice cap, does not change sea level because the ice
displaces
its volume and, hence, does not change the Earth’s rotation.
COMPRESSIONAL AND EXTENSIONAL MOVEMENT OF ICE
Compressional flow: where the gradient becomes less steep or the ice encounters a
major obstacle the ice mass slows, backs up, crevasses close and there are thrust
fractures as
the ice mass compresses. The increased thickness of ice exerts greater pressure on
bedrock
and can result in more extensive pressure erosion.
Extensional flow: where the gradient becomes steeper the ice moves faster
‘stretching’ the
ice mass and becoming thinner through a series of fractures which form crevasses at
right
angles to the direction of flow.
Basal Sliding is the act of a glacier sliding over the bed due to melt water under the
ice acting
as a lubricant. This movement very much depends on the temperature of the area, the
slope of
the glacier, the bed roughness, the amount of melt water from the glacier, and the
glacier's
size.
The movement that happens to these glaciers as they slide is that of a jerky motion
where
any seismic events, especially at the base of glacier, can cause movement. Most
movement is
found to be caused by pressured melt water or very small water-saturated sediments
underneath the glacier. This gives the glacier a much smoother surface on which to
move as
opposed to a harsh surface that tends to slow the speed of the sliding. Although melt
water is
the most common source of basal sliding, it has been shown that water-saturated
sediment can
also play up to 90% of the basal movement these glaciers make.
Warm and Cold based Glaciers
Warm based glaciers these are known as temperate glaciers and are found in lower
latitudes
such as the Alps mountain range. Due to the lower latitude, the temperature around the
glacier
allows the ice to move relatively rapidly. The process of movement is largely through
basal
slippage.
Liquid melt water plays a significant role in this process, provided by surface ice
melting
and being conveyed through the glacier via internal melt water tunnels. In addition, as
the
glacier slides downslope it further increases the temperatures at the base due to
friction and
pressure.
Cold based glaciers these are found in higher latitudes and have less seasonal
variation in
temperature than those found in the lower latitudes. Melt water is far less a presence.
These
glaciers still move but due to internal deformation/flow rather than basal slippage. They
freeze
to the bedrock and do not experience the same melting, but the role of gravity and
pressure
exerted by ice accumulation at the source causes the glacier to move.
Formation of Icebergs from Floating Glacier Tongues and Ice Shelves, and the
characteristics of each
FORMATION OF ICEBERGS
In Floating Glacier Tongue, icebergs form from a floating mass of freshwater ice that
has
broken from the seaward end of either a glacier or an ice shelf. Icebergs are found in
the
oceans surrounding Antarctica, in the seas of the Arctic and Subarctic, in Arctic fjords,
and in
lakes fed by glaciers.
Icebergs form because of the bending stress in glacier tongues (long narrow floating ice
shelves produced by fast flowing glaciers that protrude far into the ocean). The swell
causes the
tongue to oscillate until it fractures.
FORMATION OF ICEBERGS
In Ice Shelves, it receives ice in several ways: flow of ice from the continent, surface
accumulation (snowfall) and the freezing of marine ice to their undersides. Ice Shelves
lose ice
by melting from below (form relatively warm ocean currents), melting above (from
warm air
temperatures) and from the calving icebergs.
Ice Shelves are firmly attached to the land with a thickness of 2000m, with a cliff edge
that’s up
to 100m high.
Characteristics of Iceberg
 Tabular icebergs-have steep sides and a flat top like a plateau
 Non-tabular icebergs-include irregular shapes such as rounded tops, spires, sloping
sides, and
blocks.
(Wind and water erode icebergs into amazing sculptural shapes.)
Example of Tabular Iceberg Example of Non-Tubular

The Formation of Sea Ice

Sea ice is simply frozen ocean water. It forms, grows, and melts in the ocean. In
contrast,
icebergs, glaciers, ice sheets, and ice shelves all originate on land. Sea ice occurs in
both the
Arctic and Antarctic. In the Northern Hemisphere, it can currently exist as far south as
Bohai
Bay, China (approximately 38 degrees north latitude), which is actually about 700
kilometers
(435 miles) closer to the Equator than it is to the North Pole. In the Southern
Hemisphere, sea
ice only develops around Antarctica, occurring as far north as 55 degrees south
latitude.
Sea ice grows during the winter months and melts during the summer months, but
some sea
ice remains all year in certain regions. About 15 percent of the world's oceans are
covered by
sea ice during part of the year.
Sea ice is found in remote polar oceans. On average, sea ice covers about 25 million
square kilometers (9,652,553 square miles) of the earth, or about two-and-a-half times
the area
of Canada.
Sea Ice occurs primarily in the polar regions; it influences our global climate. Sea ice
has a bright surface, so much of the sunlight that strikes it is reflected back into space.
As a
result, areas covered by sea ice don't absorb much solar energy, so temperatures in the
polar
regions remain relatively cool. If gradually warming temperatures melt sea ice over
time, fewer
bright surfaces are available to reflect sunlight back into space, more solar energy is
absorbed
at the surface, and temperatures rise further.
Sea ice also affects the movement of ocean waters. When sea ice forms, most of the
salt is pushed into the ocean water below the ice, although some salt may become
trapped in
small pockets between ice crystals. Water below sea ice has a higher concentration of
salt and
is more dense than surrounding ocean water, and so it sinks. In this way, sea ice
contributes to
the ocean's global "conveyor-belt" circulation. Cold, dense, polar water sinks and moves
along
the ocean bottom toward the equator, while warm water from mid-depth to the surface
travels
from the equator toward the poles.
The difference between sea ice and ice shelves is that sea ice is free floating; the sea
freezes and unfreezes each year, whereas ice shelves are firmly attached to the land.
Sea ice
contains iceberg, thin sea ice and thick multiyear sea ice (frozen sea water that has
survived
summer melt seasons getting thicker as more ice is added each winter).
What is the difference between sea ice and icebergs, glaciers
The most basic difference is that sea ice forms from salty ocean water, whereas
icebergs,
glaciers, and lake ice form from fresh water or snow. Sea ice grows, forms, and melts
strictly in
the ocean. Glaciers are considered land ice, and icebergs are chunks of ice that break
off of
glaciers and fall into the ocean. Lake ice is made from fresh water and freezes as a
smooth
layer, unlike sea ice, which develops into various forms and shapes because of the
constant
turbulence of ocean water.
The process by which sea ice forms is also different from that of lake or river ice. Fresh
water is
unlike most substances because it becomes less dense as it nears the freezing point.
This
difference in density explains why ice cubes float in a glass of water. Very cold, low-
density
fresh water stays at the surface of lakes and rivers, forming an ice layer on the top.
Ice Tongue and Ice Shelf
Ice Tongue
The term ice tongue refers to a geographic phenomenon in which a narrow section of
ice forms
and projects directly out from the shoreline and into a nearby body of water, such as a
lake,
sea, or ocean. Typically, ice tongues protrude from the bottom of glaciers, at the point
where
the glacier runs into open lake or ocean waters. Glaciers that cause the formation of ice
tongues are principally valley glaciers, which move at a faster than average speed out
of valleys
and into waterways, and it is this speed that gives an ice tongue its shape.
The Erebus Ice Tongue is located off the coast of Ross Island, Antarctica. It has a total
length
of 6.8 miles and protrudes into the McMurdo Sound. The ice tongue is the result of the
Erebus
Glacier. Its thickness is approximately 980 feet closest to the shoreline, and only about
160 feet
thick at its tip. The Erebus Ice Tongue was first identified and mapped out in the early
20th
century by a British exploration team.
 The Drygalski Ice Tongue is located off the coast of Antarctica, toward the northern
side of the McMurdo Sound, and is roughly 150 miles north of the Erebus Ice Tongue.
The ice tongue originates from the David Glacier, which is located in Victorialand,
Antarctica. It stretches 43 miles in length and is anywhere between 9 and 15 miles in
width. The ice tongue has lost approximately 66 square miles of area after being hit by
drifting icebergs, once in 2005 and a second time in 2006. The Drygalski Ice Tongue
was first identified by the British National Antarctic Expedition near the beginning of
the
20th century.
 The Demas Ice Tongue is located off the coast of the Abbot Ice Shelf in Antarctica.
The ice shelf measures 250 miles in length and 40 miles in width. The ice tongue
protrudes into the Peacock Sound, which creates a barrier between Eights Coast and
Thurston Island. Peacock Sound feeds into Amundsen Sea. The ice tongue protrudes
about 23 miles into the sound. It was first identified in 1940, when flights controlled by
the United States Antarctic Service took off from USS Bear, which was stationed in the
area at that time.
 The Flatnes Ice Tongue is located off of the Ingrid Christensen Coast in Antarctica.
Unlike the previously mentioned ice tongues, the Flatness Ice Tongue is formed by
waters draining off the continent and into the ocean, rather than by a glacier. It
protrudes for approximately 4 miles into Prydz Bay. The ice tongue actually forms the
western barrier of Amanda Bay, separating it from Prydz Bay. It was first identified
from
aerial photos taken during expeditions that occurred during the 1930s and 1940s.
Ice Shelf
An ice shelf is a thick slab of ice, attached to a coastline and extending out over the
ocean as a
seaward extension of the grounded ice sheet. Ice shelves range in thickness from about
50 to
600 meters, and some shelves persist for thousands of years. They fringe the continent
of
Antarctica, and occupy a few fjords and bays along the Greenland and Ellesmere Island
coasts.
(An ice shelf occupying a fjord is sometimes called an ice tongue.)
Describe Pack Ice and Fast Ice
Pack ice, also known as ice pack or pack, any area of sea ice (ice formed by freezing of
seawater) that is not landfast; it is mobile by virtue of not being attached to the
shoreline or
something else. Pack ice expands in the winter and retreats in the summer in both
hemispheres
to cover about 5 percent of the northern oceans and 8 percent of the southern oceans.
Pack ice
Fast Ice
Fast ice (also called land-fast ice, landfast ice, and shore-fast ice) is sea ice that is
"fastened"
to the coastline, to the sea floor along shoals or to grounded icebergs. Fast ice may
either grow
in place from the sea water or by freezing pieces of drifting ice to the shore or other
anchor
sites. Unlike drift (or pack) ice, fast ice does not move with currents and winds.
The topography of the fast ice varies from smooth and level to rugged (when submitted
to
large pressures). The ice foot refers to ice that has formed at the shoreline, through
multiple
freezing of water between ebb tides, and is separated from the remainder of the fast ice
surface by tidal cracks. Further away from the coastline, the ice may become anchored
to the
sea bottom—it is then referred to as bottom fast ice.
Fast ice can survive one or more melting seasons (i.e. summer), in which case it can be
designated following the usual age-based categories: first-year, second-year, multiyear.
The fast ice boundary is the limit between fast ice and drift (or pack) ice—in places, this
boundary may coincide with a shear ridge. Fast ice may be delimited or enclose
pressure ridges
which extend sufficiently downward so as to be grounded—these features are known
as stamukhi.
The normal seasons and probable tracks of North Atlantic bergs from origin to decay
At present, several icebergs are drifting out of the Arctic Ocean and into the North
Atlantic. This natural phenomenon occurs each year in the period roughly stretching
between
April and August. During this season, these massive chunks of ice cross the major
shipping
routes on the North Atlantic. But Hapag-Lloyd is prepared for them, as the company’s
captains
keep their vessels south of the drift ice limit so as to avoid any dangerous collisions.
The authorities recently reported that there are more icebergs this year than usual.
For
example, in the first week of April, the International Ice Patrol operated by the U.S.
Coast
Guard warned of 450 icebergs, even though the average for this time of year is only a
bit above
80.
In addition to containerships, bulk carriers and fishing vessels also bypass the
dangerous
areas. However, reducing speed in order to be able to stick closer to the ideal route is
not an
option. “Even if the captain sails more slowly, the problem does not go away, as it is
generally
hard to spot icebergs, even on the radar,” Werth explains. “As we know, the larger part
of the
icebergs is located underwater, and you cannot readily gauge their actual dimensions.”
The principal origin of those icebergs that reach the North Atlantic Ocean are the 100
or
so major tidewater glaciers of West Greenland. Between 10,000 to 15,000 icebergs are
calved
each year, primarily from 20 major glaciers between the Jacobshaven and Humboldt
Glaciers.
Glaciers are formed by thousands of years of snowfall accumulation which eventually is
compressed into ice. It is estimated that these glaciers account for 85% of the icebergs
which
reach the Grand Banks of Newfoundland. Other sources of icebergs are the East
Greenland
glaciers, which produce about half the amount of icebergs as the West Greenland
glaciers, but
account for only 10% of the icebergs reaching the Grand Banks. The remaining 5% are
thought
to come from glaciers and ice shelves of northern Ellesmere Island.
In order for an iceberg to reach the North Atlantic the currents typically take it from
Baffin Bay through the Davis Strait and Labrador Sea. This is a long trip and most
icebergs
never make it. Most icebergs melt well before entering the Atlantic Ocean. One
estimate is that
of the 15,000 to 30,000 icebergs produced annually by the glaciers of Greenland only
one
percent (150 to 300) ever make it to the Atlantic Ocean. When an iceberg does happen
to reach
the Atlantic its long and traveled life quickly comes to an end melting rapidly in the
warm
waters.
The outer limits of area in which icebergs may be encountered in the North Atlantic
An iceberg is a large piece of ice that has broken away (or calved) from a glacier and is
at
least 5m above sea level. Icebergs are categorized by size from very large (over 75
meters high
and 200 meters wide) to growler (less than 1 meter high and less than 5 meters wide).
Across the Grand Banks, the most active months of the iceberg season (from March to
May) create the most problems for shipping lanes across the North Atlantic. During a
typical
season, icebergs can migrate as far south as 39N across the Grand Banks. The farthest
south
an iceberg has been spotted was in 1926 near 30-20N/62-32W, approximately 150nm
northeast
of Bermuda. Vessels typically maintain at least 30 to 60 nautical miles safe berth south
of the
limit of all known icebergs as issued by the IIP, which usually means additional distance
steamed for trans-Atlantic vessels proceeding to Newfoundland, Nova Scotia, and New
England.
The International Ice Patrol (IIP) monitors the shipping lanes of the North Atlantic near
the
Grand Banks for icebergs year round. During the iceberg season, which generally runs
from
February 15 to June 01, iceberg advisories and charts are issued by the IIP. These
advisories
delineate the southern limit of all known icebergs and show the icebergs’ location and
density.
Icebergs regularly break off from glaciers in the Arctic and make their way south to the
North
Atlantic Ocean, where they can come into contact with ships. The number of icebergs
found in
the North Atlantic Ocean changes from year to year.
A deep, cold ocean current flows down from the North Pole, around the
Canadian province of Newfoundland and Labrador, to meet the warm Gulf Stream
traveling
north from the Gulf of Mexico. Called the Labrador Current, it passes by the Arctic’s
premier
iceberg nursery off the coast of west Greenland. There, icebergs calve in great
numbers,
breaking off glaciers to float freely in the ocean. They drift northward up the coast until
they
meet the Labrador, then ride south in huge masses toward Newfoundland. Nowhere
else in the
world does this much ice intersect major shipping routes. The region deserves its
nickname: Iceberg Alley.
Normal and Extreme limits of Icebergs travel in the Southern Oceans during
Summer and Winter
In Southern hemisphere, In winter the Antarctic sea ice normally extends to between
latitudes
of 65 degrees and 55 degrees South, thus prevailing great circle sailing between the
Capes to
anyone bold enough to attempt it in a small vessel.
Even in summer, sailing high latitudes in the southern ocean southward of about 55
degrees
South is hazardous due to large numbers of icebergs. On the other hand several coasts
within
the polar regions become accessible in summer.
Reasons for the decay of Icebergs
Icebergs are pieces of ice that formed on land and float in an ocean or lake. Icebergs
come in
all shapes and sizes, from ice-cube-sized chunks to ice islands the size of a small
country. The
term "iceberg" refers to chunks of ice larger than 5 meters (16 feet) across. Smaller
icebergs,
known as bergy bits and growlers, can be especially dangerous for ships because they
are
harder to spot. The North Atlantic and the cold waters surrounding Antarctica are home
to most
of the icebergs on Earth.
Icebergs form when chunks of ice calve, or break off, from glaciers, ice shelves, or a
larger
iceberg. Icebergs travel with ocean currents, sometimes smashing up against the shore
or
getting caught in shallow waters.
When an iceberg reaches warm waters, the new climate attacks it from all sides. On the
iceberg surface, warm air melts snow and ice into pools called melt ponds that can
trickle
through the iceberg and widen cracks. At the same time, warm water laps at the
iceberg edges,
melting the ice and causing chunks of ice to break off. On the underside, warmer
waters melt
the iceberg from the bottom up.
Icebergs pose a danger to ships traversing the North Atlantic and the waters around
Antarctica. After the Titanic sank near Newfoundland in 1912, the United States and
twelve
other countries formed the International Ice Patrol to warn ships of icebergs in the
North
Atlantic.
The International Ice Patrol uses airplanes and radars to track icebergs that float into
major shipping lanes. The U.S. National Ice Center uses satellite data to monitor
icebergs near
Antarctica. However, it only tracks icebergs larger than 500 square meters (5,400
square feet).
Icebergs can also serve as tools for scientists, who study them to learn more about
climate and ocean processes.
Decay of Icebergs
As icebergs travel southwards towards the coast of Newfoundland, they experience
significant
reductions in their numbers and size. Many icebergs melt more quickly when they move
outside
the ice pack. Icebergs that leave the pack will become grounded or be decayed
gradually by
wave action. The pack ice extends the life of an iceberg by:
 Dampening waves at the edge of the pack, reducing erosion.
 Keeping the water temperature within the pack near freezing.
 Keeping the iceberg from becoming grounded.
 Icebergs reaching the Grand Banks will have lost about 85% of their original mass.
Most of the melting of an iceberg takes place on its submerged surface because of the
high
density and thermal conductivity of sea water. However, iceberg melt is the combined
result of
many processes that vary over time and space along with the iceberg's physical
properties. The
main causes of iceberg melt are:
Insolation,
Water convection,
Air convection and
Wave erosion
Insolation
Solar radiation is known to have little effect in iceberg melt. However, radiation may
have a
considerable effect on calving through the creation of thermal stress in the surface
layer of the
iceberg.
Water Convection
This is the natural convection of buoyant melt water which is less dense than sea water
moving up an iceberg's sides. When ice melts in sea water, the melting process
produces both
cooling and dilution which have opposite effects on the sea water density. Cooling
produces
more dense water while dilution produces less dense water. The saline effect (dilution)
dominates above the lowest meter or so of the vertical ice wall.
Air Convection
Arctic icebergs, which are relatively small in mass compared to ice islands or Antarctic
icebergs, often get caught in the strong prevailing winds of the Labrador Sea/Grand
Banks
regions. These winds have been estimated to move the icebergs at velocities of 10-30
cm/sec
above local water current speeds. In addition, the air convection induced melt rate is
significantly higher than that from natural water convection.
It should be noted that velocity differences between the air near the iceberg surface
and
the wind also produce melt but at a much smaller rate than that for water convection.
Wave Erosion
Wave erosion at the waterline of an iceberg is the most important deterioration
mechanism. Waves can rapidly, even in cold water, erode a notch or crevasse into an
iceberg
after which calving or fracture can occur. As these notches proceed deeper into the
berg, they
leave an overhanging slab protruding above the waterline. At some critical length the
stresses
due to the weight of the slab will cause fracture and calving of the slab.
It should be noted that calving time decreases significantly with increasing wave
height.
Wave action is a very efficient way to dissipate the cooling effect of a berg and keep a
supply of
warmer water at the edge of the iceberg.
Areas affected by Sea Ice in Regions frequented by Shipping
Arctic shipping routes are the maritime paths used by vessels to navigate through parts
or
the entirety of the Arctic. There are three main routes that connect the Atlantic and the
Pacific
oceans: The Northeast Passage, the Northwest Passage, and the Transpolar Sea Route.
Northeast Passage, also called Northern Sea Route, Russian Severny Morskoy Put,
or Severoput, maritime route through the Arctic along the northern coast of the
Eurasian
landmass, principally situated off the coast of northern Siberia (Russia).
Northeast Passage was of a channel that traversed the entire distance between
the Atlantic and Pacific oceans, constituting the Eurasian equivalent of the fabled
Northwest
Passage across Arctic North America. Specifically, the Northeast Passage stretches
generally
eastward via the ice-free Norwegian and Barents seas around the Scandinavian
Peninsula and
across northwestern Russia to the Kara Strait, which separates the Barents and Kara
seas.
Northeast Passage between the Kara and Bering straits remains icebound for most of
the year
and thus is the most difficult for ships to transit. However, first the Soviet Union and
then
Russia developed and maintained a navigable channel roughly 3,500 miles (5,600 km)
in
length—the distance can vary significantly, depending on the route followed—through
this most
challenging part of the passage.
New research from York University predicts that it will be decades before the
Northwest
Passage will be a viable route for regular commercial shipping. Despite climate change,
Arctic
sea ice remains too thick and treacherous.
The Northwest Passage is a sea route that connects the Atlantic and Pacific Oceans
through the Canadian Arctic Archipelago.
In the past, the Northwest Passage has been virtually impassable because it was
covered by thick, year-round sea ice.
For commercial shipping, the potential benefits of a clear Northwest Passage are
significant.
The Northwest Passage is a much shorter route for moving goods between the Pacific
and
Atlantic regions than the Panama and Suez Canals. Ship routes from Europe to eastern
Asia
would be 4,000 kilometers (2,500 miles) shorter. Alaskan oil could move quickly by ship
to ports
in the eastern United States. The vast mineral resources of the Canadian North will be
much
easier and economical to develop and ship to market.
Transpolar Sea Route (TSR) is a future Arctic shipping route running from the Atlantic
Ocean to the Pacific Ocean across the center of the Arctic Ocean. The route is also
sometimes
called Trans-Arctic Route.
The Transpolar Sea Route represents the most direct route for trans-Arctic shipment
but
has yet to attract significant commercial interest, as multi-year ice remains a
formidable
obstacle for most of the Arctic shipping season.
The effects of climate change are, however, increasingly observed throughout the
region and
the Arctic is now warmer than it has been at any time during the last 2,000 years.
Summer ice
extent has declined by 40% since satellite observation began in 1979. Over the same
period,
Arctic sea ice has thinned considerably, experiencing a decline in average volume of
70%.
Within the next decade this warming trend may transform the region from an
inaccessible
frozen desert into a seasonally navigable ocean and the Arctic Ocean may be ice-free
for short
periods as early as 2015.
Seasonal Development and Recession of Sea Ice on the Coastlines of the Northern
Oceans, and in the Latitude of the Normal Trade Routes
An unprecedented analysis of North Pacific Ocean circulation over the past 1.2 million
years has
found that sea ice formation in coastal regions is a key driver of deep ocean circulation,
influencing climate on regional and global scales. Coastal sea ice formation takes place
on
relatively small scales, however, and is not captured well in global climate models.
When sea ice forms, it expels salt into the surrounding water, increasing the density of
the water and causing it to sink, carrying oxygenated surface water into the depths.
One result
is a flow of cold deep water toward the equator and warm surface water toward the
poles, and this "overturning circulation" plays a crucial role in moving heat around the
globe.
This process (also called “Thermohaline circulation") has received less attention in the
North
Pacific than in the North Atlantic, where the formation of North Atlantic Deep Water is
a
powerful driver of global ocean circulation and climate. In the North Pacific,
overturning
circulation driven by formation of the North Pacific Intermediate Water is not as strong
as in the
North Atlantic, but it plays a major role in the region's climate.
Seasonal Development
By far the greatest seasonal changes in the ice thickness distribution of the East
Antarctic pack
are in the open water and thin ice categories. The amount of open water decreases
from almost
60% in December to little more than 10% in August, and the thinnest ice thickness
category (0
- 0.2 m) shows a 30% seasonal change between December and March.
In contrast, the amount of ice greater than 1.0 m shows very little seasonal variability.
This is because undeformed ice rarely exceeds 1 m thick, and the deformed ice greater
than 1
m thick only comprises a small fraction of the pack, with the nature of the ice drift
largely
preventing the accumulation of the thicker ice to form multi-year ice.
Recession of Sea Ice
July is typically the warmest month of the year, with the largest rate of ice loss. Sea ice
extent
this July declined at an average rate of 105,700 square kilometers (40,800 square miles)
per
day, exceeding the 1981 to 2010 average of 86,800 square kilometers (33,500 square
miles)
per day.
Rapid ice loss for July 2019 was in part driven by warm conditions during the first half
of
the month. The latter half of the month, in contrast, was relatively cool over the East
Siberian
and Laptev Seas, as well as near Svalbard and the Canadian Arctic Archipelago.
By the beginning of August, the pace of ice loss tends to drop rapidly. 2012 was an
exception, when the average August ice loss rate remained quite rapid at 89,500 square
kilometers per day (34,600 square miles per day), leading to a new record low for the
September minimum that year.
As of August 5, 2019, the total sea ice extent has dropped below 6 million square
kilometers,
something which has not occurred prior to 1999. Sea ice extent in September of 2019 is
likely
to be among the five lowest minimums recorded.
In total, sea ice extent during July 2019 decreased by 3.28 million square kilometers
(1.27
million square miles). This was larger than the 1981 to 2010 average loss for the month.
The
linear rate of sea ice decline for July from 1979 to 2019 is 693,000 square kilometers
(268,000
square miles) per year, or 7.32 percent per decade relative to the 1981 to 2010
average.