TYPHOONS

Tamayosa, Alexis
Siton, Cressan
Bucayong, Vemryzill.
 Typhoons
An intense tropical cyclone.

A severe weather disturbance.

 Section Objectives
1. Characterize typhoons and other types of tropical cyclones.
2. Be familiarize with the structure and seasonal variability of
typhoon.
3. Be acquainted with how tropical cyclones are formed and
how they behave.
4. Be acquainted by the different methods employed in
tropical cyclone forecasting and monitoring.
5. Identify areas prone to effects of typhoons.
6. Know what to do before, during, and after a typhoon.
 Typhoons

A typhoon is a severe weather disturbance characterized by

strong winds and heavy rains which revolve around a central
low pressure area.
It is the most powerful type of tropical cyclone that forms in
the northwestern Pacific Ocean.
 Typhoons

"Tai Fung" from a chinese word meaning big wind.

Locally known as "bagyo" ; a term coined after Baguio City in

Benguet Province where the wettest known tropical cyclone
way back in 1911 hit and dropped approximately 2200mm of
rainfall for about 3 days.
 Typhoons

It is one of three types of tropical cyclones.

Can be distinguished according to their maximum

sustained-wind speed (over 10min periods.)
 Typhoons
Tropical Depression: wind speed up to 62kph.

Tropical Storm: wind speed ranging from 63-118kph.

Typhoon: exceeding 118kph.

Super Typhoon: exceeding 220kph.

 Philippines

The most frequently visited country by tropical cyclones. A

yearly average of 19 entering the Philippine Area of
Responsibility (PAR) and 6 to 9 making landfall. Areas usually
most affected are 'northern and central Luzon' & 'eastern
Visayan islands.'
Bagyong Vamco(Ulysses), Luzon at
November 11, 2020
 Seasonal Variability
Philippines belong to the northwest Pacific Ocean that creates
the most intense and frequent occurence of tropical cyclones.

Tropical cyclone activity is usually lowest in May and increases

gradually though June. Activity then greatly increases from
July until September with the level reaching its highest during
August. November, activity level eventually dies off.
Notable, however, typhoon Haiya(Yolanda) struck in November
2013. Death tolls allegedly reached 6000 according to the
NDRRMC.
 Structure

A tropical cyclone has an average total diameter of 550km

but can have a diameter more than 2000km wide. It's basic
structure consists of an eye, an eye wall, and surrounding
rain bands.
 The Eye

The lowest atmospheric pressure in the structure of a tropical

cyclone. Atmospheric pressure decreases from the outer most
portion toward the eye.
With diameter 20-65km wide, winds are weak, the temperature
is warm and the sky is clear. As if there was no storm to begin
with, but it is only shortlived.
 The Eye Wall

The region immediately surrounding the tropical cyclones

center and which can reach as high as 15km above mean sea
level, brings the strongest winds, heavy rains, and turbulence
shortly after the passage of the eye.
 Rain bands
Are spiraling strips of clouds in the fringes of tropical cyclones
which are associated with rainfall. The winds of tropical cyclone
blow counter clockwise in the Northern Hemisphere and
clockwise in the Southerm Hemisphere due to the Coriolis
effect.
The Coriolis effect describes the deflection of an object's
motion due to earth's rotation about its axis.
In the northern hemisphere, the air deflects to the right; the
southern hemisphere to the left.
 Why do cyclones
form?
They form as a result of atmosphere's natural tendency to
maintain equilibrium by redistributing heat through wind
from the equatorial regions to the polar regions. This
mechanism prevents the tropical areas from getting
excessively hot and the polar regions from becoming
extremely cold.
 Importance
If not for tropical cyclones, there would be severe
environmental imbalances. Rainfall brought about by
tropical cyclones replenishes ground water and surficial
water. Flora and fauna in the Philippines are heavily reliant
on tropical cyclones for source of water. Almost 50% of the
average annual rainfall in the country is derived from
typhoon-related rainfall.
 Formation?
Tropical cyclones form both in the northern and southern
hemisphere at latitudes 5 to 30 degrees away from the
equator(trade-wind belt) in parts of the open ocean where
water temperatures reach at least 26degreeCelsius to
depth of more than 60 meters.
Toward the end of the summer warm moist air forms the
most. The air mass heats up and rises, causing the
atmospheric pressure beneath to drop.
 Formation?
Air masses from the surrounding higher pressure areas
tend to flow to this area of low pressure and also heat up
and rise. However, due to the Coriolis effect, it won't travel
straight but swirls around the central low pressure area.
The rising humid air accumulates at cooler higher altitudes
to form cumulonimbus clouds(mushroom shaped clouds.)
 Formation?
But these also get dragged by the force of the incoming
rotating air masses and form long swirling cloud bands. A
point comes when the water vapor that form the clouds
condense and cause heavy rainfalls.
Drier air from higher altitudes is sucked on the center,
preventing the formation of clouds, therefore, rainfall. It is
why the eye of the tropical cyclone is calm.
If warm air is evaporating from the ocean, the tropical
cyclone is like a machine operating on this supply of
energy.
 Tropical Cyclone

A tropical cyclone typically has a life span of nine days and can
travel more than 10,000km. Tropical cyclones that form in the
Pacific Ocean and South China Sea frequently affects the
Philippines.
Effects of
Tropical
Cyclones
Effects of Tropical Cyclones

One of the most destructive natural phenomena worldwide.

Countless casualties and indescribable damage to property in
many countries
 Coastal Areas

The effects of tropical cyclones are the worst along

coastal areas where they first make landfall. It brings with
them very strong winds, heavy rains, and can cause
flooding and storm surges.
 Strong Winds
They cover a much larger area during tropical cyclones, cuase
the most obvioous damage. Because the winds are strongest in
the eyewall, meteorologist are on the watch for the locations
where the eye(and eye wall) will make landfall. Wind usually
slows down upon making landfall and reduces speed down to
almost half its original speed 7 hours after crossing the
coastline. This might not always be the case, as some do
actually pick up speed.
 Storm Surge
Localized unusual increase of sea water level way above the
predicted astronomical tide level, happens primarily due to
intense winds and lowered atmospheric pressure that
accompany intense tropical cyclones passing from the sea to
land. People living near the coast and rivers where water from
the sea could potentially enroach are encouraged to flee inland
as far and as high as possible, as early as the first warning of
the possible landfall.
 Heavy Rains

Unlike the last two, heavy rains actually occur in tropical

cyclones of lower intensity. Flooding due to heavy rain is
usually worse during tropical depressions and tropical storms.
However, rainfall that accompanies tropical cyclones can also
be beneficial. Rains brought by tropical cyclones fulfill the
water needs of some areas they cross.
 Measures for
Mitigating the
Destructive Effects of
Typhoons
 1. Determining areas prone to typhoon-related disasters
Observation of typhoon paths allow 'typhoon paths' to
be established. The path might U-turn but 'typhoon paths'
are mostly reliable.
Geohazard maps made by Geosciences Bureau(MGB) and
(DENR) can be consulted to determine which areas prone
to landslide.
The country's typhoon belt has shifted from northern
Luzon to southern Luzon and the Visayas island.
2. Implementing legislation involving land use planningg,
zoning, and building standards
Risky areas should not be used by commercial use such as
farming area or nature reserve. Agreements on the
mandated government should discourage people
inhabiting high risk areas.
Building permits to ensure strict abidance to prescribed
desgins to avoid typhoon-related disasters.
3. Weather forecasting and monitoring
effective forecasting of tropical cyclones gives ample time
for communities to prepare, secure property, and to seek
refuge if necessary. It gives a lead time for the different
businesses involved, like agriculture, transportation, and
energy generation to make decisions and necessary
arangements to minimize the possible losses.
4. Effective public typhoon warning systems
PAGASA is the country's official weather bureau. It's in
charge of monitoring storms. The release warniings in the
form of Public Storm Warning Signals. The following are
the current warning signals:

PSWS #1-Tropical cyclone winds of 30km/h within the next

36 hours. Winds expected to bring damage but may bring
very light damage.
PSWS #2 Tropical cyclone winds of 61-120km/h within 24
hours. light to moderate damage.
PSWS #3 Tropical Cyclone winds of 121-170km/h within 18
hours. Moderate to heavy damage.
PSWS #4 Tropical Cyclone winds of 171-220km/h within 12
hours. Heavy to very heavy damage.
PSWS #5 Tropical Cyclone winds of more than 220km/h
are expected within 12 hours. Very heavy to widespread
damage.
 PAG-ASA
They play an important role of operating a nationwide
network for forecasting and observing tropicalcyclones
that may enter or affect thr Philippine Area of
Responsibility (PAR) while the Regional Specialized
Meteorological Center(RSMC) Tokyo-Typhoon Center of
the Japan Meteorological agency is one of the worldwide
Tropical Cyclone RSMCs in charge of official warnings for
the entire Western Pacific Ocean and South China Sea
Region.
 RSMC
Responsible for detecting typhoons on their own regional
area(s). The RSMC Tokyo-Typhoon Center of the Japan
Meteorological Agency is also in charge of naming
typhoons. This ist is a compilation of names of flowers,
animals, astrological signs, and people. The names are
arranged into five columns and are used in the exact order
per column. If the last storm in the previous year was
Toraji(Column2 Row3), the name of the first storm this
year will be Man-yi(COlumn2 Row4).
 PSWS

The old PSWS scheme was composed of

only 4 phases. The new system is a more
refined version of the old PSWS.
 Assessment
1. Why is the Philippines frequented by typhoons?
2. Why do super typhoons like Yolanda happen? What are
the circumstances by which perfect storms occur?
3. Explain why tropical cyclones does not take a straight
path.
4. Cite four personal measures that you consider most
important in avoiding or minimizing the effects of
typhoons.