Tropical cyclones are ranked on one of five tropical cyclone intensity scales, according to their

maximum sustained winds and which tropical cyclone basin(s) they are located in. Only a few
scales of classifications are used officially by the meteorological agencies monitoring the tropical
cyclones, but other scales also exist, such as accumulated cyclone energy, the Power Dissipation
Index, the Integrated Kinetic Energy Index, and the Hurricane Severity Index.

Tropical cyclones that develop in the Northern Hemisphere are unofficially classified by the
warning centres on one of three intensity scales. Tropical cyclones or subtropical cyclones that
exist within the North Atlantic Ocean or the North-eastern Pacific Ocean are classified as either
tropical depressions or tropical storms. Should a system intensify further and become a
hurricane, then it will be classified on the Saffir–Simpson hurricane wind scale, and is based on
the estimated maximum sustained winds over a 1-minute period. In the Western Pacific, the
ESCAP/WMO Typhoon Committee uses four separate classifications for tropical cyclones that
exist within the basin, which are based on the estimated maximum sustained winds over a 10-
minute period.

The India Meteorological Department's scale uses 7 different classifications for systems within
the North Indian Ocean, and are based on the systems estimated 3-minute maximum sustained
winds. Tropical cyclones that develop in the Southern Hemisphere are only officially classified
by the warning centres on one of two scales, which are both based on 10-minute sustained wind
speeds: The Australian tropical cyclone intensity scale is used to classify systems within the
Australian or South Pacific tropical cyclone basin. The scale used to classify systems in the
South-West Indian Ocean is defined by Météo-France for use in various French territories,
including New Caledonia and French Polynesia.

The definition of sustained winds recommended by the World Meteorological Organization

(WMO) and used by most weather agencies is that of a 10-minute average at a height of 10 m
(33 ft) above the sea surface. However, the Saffir–Simpson hurricane scale is based on wind
speed measurements averaged over a 1-minute period, at 10 m (33 ft). The scale used by RSMC
New Delhi applies a 3-minute averaging period, and the Australian scale is based on both 3-
second wind gusts and maximum sustained winds averaged over a 10-minute interval. These
differences make direct comparisons between basins difficult.

Within all basins tropical cyclones are named when the sustained winds reach at least 35 kn
(40 mph; 65 km/h).

Contents
 1 Background
 2 Atlantic, Eastern and Central Pacific
 3 Western Pacific
 4 North Indian Ocean
 5 South-West Indian Ocean
  6 Australia and Fiji
 7 Alternative scales
 8 Comparisons across basins
 9 See also
 10 References
 11 External links

Background
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Tropical cyclones are defined as being warm cored, non-frontal synoptic cyclones, that develop
over tropical or subtropical waters, with organized atmospheric convection and have a definite
cyclonic surface wind circulation. They are classified by the wind speeds located around the
circulation centre and are ranked, by the World Meteorological Organization's Regional
Specialized Meteorological Centers on one of five tropical cyclone scales. The scale used for a
particular tropical cyclone depends on what basin the system is located in; with for example the
Saffir–Simpson hurricane wind scale and the Australian tropical cyclone intensity scales both
used in the Western Hemisphere. All of the scales rank tropical cyclones using their maximum
sustained winds, which are either observed, measured or estimated using various techniques,
over a period between one and ten minutes.

Atlantic, Eastern and Central Pacific

Saffir–Simpson scale
Wind speeds
Category (for 1-minute maximum sustained winds)
m/s knots (kn) mph km/h
Five ≥ 70 m/s   ≥ 137 kn   ≥ 157 mph   ≥ 252 km/h  
Four   58–70 m/s     113–136 kn     130–156 mph     209–251 km/h  
Three   50–58 m/s     96–112 kn     111–129 mph     178–208 km/h  
Two   43–49 m/s     83–95 kn     96–110 mph     154–177 km/h  
One   33–42 m/s     64–82 kn     74–95 mph     119–153 km/h  
Related classifications
(for 1-minute maximum sustained winds)
Tropical storm   18–32 m/s     34–63 kn     39–73 mph     63–118 km/h  
Tropical depression   ≤ 17 m/s     ≤ 33 kn     ≤ 38 mph     ≤ 62 km/h  
Main article: Saffir–Simpson scale

Tropical cyclones that occur within the Northern Hemisphere to the east of the anti-meridian, are
officially monitored by either the National Hurricane Center or the Central Pacific Hurricane
Center.[1] Within the region a tropical cyclone is defined to be a warm cored, non-frontal synoptic
disturbance, that develops over tropical or subtropical waters, with organized atmospheric
convection and a closed well defined circulation centre.[1] The region also defines a subtropical
cyclone as a non-frontal low pressure disturbance, that has the characteristics of both tropical and
extratropical cyclones.[1] Once either of these classifications are met, then advisories are initiated
and the warning centers will classify the system as either a tropical or subtropical depression, if
the one-minute sustained winds estimated or measured as less than 34 kn (38 mph; 62 km/h).[1]

Also, it will be assigned a tropical cyclone number (or TC number for short) comprising an
officially spelled-out number (from ONE to THIRTY or less; these numbers are not recycled until
next year) followed by (except for North Atlantic systems) a hyphen and a suffix letter ("-E" for
East Pacific, "-C" for Central Pacific);[2] a two-digit (plus any suffix) abbreviation (like TD 08 for
North Atlantic depression EIGHT, TD 21E for East Pacific depression TWENTYONE-E, or TD
03C for Central Pacific depression THREE-C) is also generated for bulletin and other automated
purposes.

However, if a tropical disturbance is capable of producing tropical storm or hurricane conditions

on land within 48 hours, then advisories will be initiated and it will be classified as a potential
tropical cyclone (PTC)[1] with a two-digit PTC number (for example, PTC-09 or PTC-15E) that
otherwise looks identical to a TC number. Should the system intensify further or already have
one-minute sustained winds of 34–63 kn (39–73 mph; 63–118 km/h), then it will be called either
a tropical or subtropical storm and assigned a name[1] (which replaces the spelled-out TC
number; the two-digit number is still kept for purposes like the Automated Tropical Cyclone
Forecasting System, as in 2018's TS 12 (KIRK)).

Should the tropical system further intensify and have winds estimated or measured, as greater
than 64 kn (74 mph; 119 km/h), then it will be called a hurricane and classified on the Saffir–
Simpson hurricane wind scale.[1] The lowest classification on the SSHWS is a Category 1
hurricane, which has winds of between 64 and 82 kn (74–95 mph, 119–153 km/h).[1][3] Should the
hurricane intensify further then it will be rated as a Category 2 hurricane, if it has winds of
between 83 and 95 kn (96–110 mph, 154–177 km/h).[1][3] When a system becomes a Category 3
hurricane with winds of between 96 and 112 kn (111–129 mph, 178–208 km/h), it is considered
to be a major hurricane by the warning centers.[3] A Category 4 hurricane has winds of 113–
136 kn (130–156 mph, 209–251 km/h), while a Category 5 hurricane has winds of at least 137 kn
(157 mph, 252 km/h).[1][3] A post tropical cyclone is a system that has weakened, into a remnant
low or has dissipated and formal advisories are usually discontinued at this stage.[1] However,
advisories may continue if the post tropical cyclone poses a significant threat to life and property.
[1]
They may also continue if the remnants of the system have a chance of regeneration and
producing tropical storm or hurricane-force winds over land within 48 hours.[1]

The SSHS was originally created using both wind speed and storm surge, but since the
relationship between wind speed and storm surge is not necessarily definite, the scale was
changed to the "Saffir–Simpson Hurricane Wind Scale" (SSHWS), based entirely on wind speed.

Although increasing echelons of the scale correspond to stronger winds, the rankings are not
absolute in terms of effects. Lower-category storms can inflict greater damage than higher-
category storms, depending on factors such as local terrain, population density and total rainfall.
For instance, a Category 2 hurricane that strikes a major urban area will likely do more damage
than a large Category 5 hurricane that strikes a mostly rural region. In fact, tropical systems of
less than hurricane strength can produce significant damage and human casualties, especially
from flooding and landslides.

Historically, the term great hurricane was used to describe storms that possessed winds of at
least 110 kn (125 mph; 200 km/h), large radii (over 160 km / 100 mi) and that caused large
amounts of destruction. This term fell into disuse after the introduction of the Saffir–Simpson
scale in the early 1970s.[4]

A minor change to the scale was made ahead of the 2012 hurricane season, with the wind speeds
for Categories 3–5 tweaked to eliminate the rounding errors that had occurred during previous
seasons, when a hurricane had wind speeds of 115 kn (130 mph; 215 km/h).[5]