Tropical cyclone scales

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Tropical cyclones are ranked according to their maximum winds using several scales. These scales are provided by several bodies, including the World Meteorological Organization, the National Hurricane Center, and the Bureau of Meteorology. The National Hurricane Center uses the Saffir-Simpson scale for hurricanes in the eastern Pacific and Atlantic basins. Australia uses a difference set of tropical cyclone categories for their region. Many basins have different names for storms of hurricane/typhoon/cyclone strength. The use of different definitions for maximum sustained wind creates additional confusion into the definitions of cyclone categories worldwide.

Atlantic and East Pacific

Template:Saffir-SimpsonTemplate:Main The Saffir-Simpson Hurricane Scale is the classification system used for Atlantic hurricanes and East Pacific (up to 140° W) hurricanes. A Category 1 storm has the lowest maximum winds, a Category 5 hurricane has the highest. 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 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.

The U.S. National Hurricane Center classifies hurricanes of Category 3 and above as major hurricanes. The U.S. Joint Typhoon Warning Center classifies typhoons with wind speeds of at least 150 mph (67 m/s or 241 km/h, equivalent to a strong Category 4 storm) as Super Typhoons. The term major hurricane supplants the previously used term of great hurricane which was used throughout the 1950s and 1960s.

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) . The U.S. weather service defines sustained winds based on 1-minute average speed, also measured 10 m (33 ft) above the surface.[1][2]

South Pacific

The Australian Bureau of Meteorology uses a 1-5 scale called tropical cyclone severity categories. Unlike the Saffir-Simpson Hurricane Scale, severity categories are based on estimated maximum wind gusts, which are a further 30-40% stronger than the 10-minute average sustained winds.[3] Severity categories are scaled lower than the Saffir-Simpson Scale - for example, a severity category 2 tropical cyclone is roughly equivalent to a strong tropical storm or a weak Saffir-Simpson category 1 hurricane.[4]

Australian Category[5] Maximum wind gusts (km/h) Maximum sustained winds (km/h)[6] Corresponding Beaufort Force[7]
Effects[8]
Category 1 ≤125 63-88 Gale (8-9)
Negligible house damage. Damage to some crops, trees and caravans.
Category 2 125-169 89-117 Storm (10-11)
Minor house damage. Significant damage to signs, trees and caravans. Heavy damage to some crops. Risk of power failure. Small craft may break moorings.
Category 3 170-224 118-159 Hurricane (12)
Some roof and structural damage. Some caravans destroyed. Power failures likely.
Category 4 225-279 160-199 Hurricane (12)
Significant structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures.
Category 5 ≥280 ≥200 Hurricane (12)
Extremely dangerous with widespread destruction.

The sustained winds given in the table are based on a 10-minute average.[3]

West Pacific

Japan, the Philippines, Hong Kong, Macau and Taiwan use the following scale to classify tropical cyclones. This scale is also for regional exchange among Typhoon Committee members. [9]

Classification Maximum sustained winds (km/h) Maximum sustained winds (knots) Corresponding Beaufort Force
Tropical Depression ≤62 ≤33 Near gale (≤7)
Tropical Storm 63–88 34–47 Gale (8–9)
Severe Tropical Storm 89–117 48–63 Storm (10–11)
Typhoon ≥118 ≥64 Hurricane (12)
NASA QuikSCAT image of Typhoon Nesat (2005) showing the near-surface winds generated by the storm 10 meters above the ocean. With winds of 213 kilometers per hour (115 knots or 132 mph) and gusts to 259 km/h (140 knots or 161 mph), Nesat was a Category 4 storm.

Note:

  • The sustained winds given in the table are based on a 10-minute average.
  • Japan and Taiwan use another scale in their own language.
  • The Philippines merges the category "Severe Tropical Storm" with "Tropical Storm" when issuing public advisories.
  • China uses a very similar scale except for the following:
    • 2-minute sustained winds are used.[10]
    • The sustained winds of Tropical Depression is defined as being equivalent to a Beaufort force 6–7, i.e. a lower limit is set.[11]
    • Typhoon is further divided into three categories since the sudden introduction of the extended Beaufort scale on May 15, 2006. The sustained winds of Typhoon, Severe Typhoon, and Super Typhoon are defined as being equivalent to a Beaufort force 12–13, 14–15, and 16–17, respectively.[12][13]

Comparisons across basins

The terminology for tropical cyclones differs from one region to another. Below is a summary of the classifications used by Regional Specialized Meteorological Centers worldwide:[14]

Tropical Cyclone Classifications (all winds are 10-minute averages)
Beaufort scale 10-minute sustained winds (knots) N Indian Ocean
IMD
SW Indian Ocean
MF
Australia
BOM
SW Pacific
FMS
NW Pacific
JMA
NW Pacific
JTWC
NE Pacific &
N Atlantic
NHC & CPHC
0–6 <28 Depression Tropical Disturbance Tropical Low Tropical Depression Tropical Depression Tropical Depression Tropical Depression
7 28-29 Deep Depression Tropical Depression
30-33 Tropical Storm Tropical Storm
8–9 34–47 Cyclonic Storm Moderate Tropical Storm Tropical Cyclone (1) Tropical Cyclone Tropical Storm
10 48–55 Severe Cyclonic Storm Severe Tropical Storm Tropical Cyclone (2) Severe Tropical Storm
11 56–63 Typhoon Hurricane (1)
12 64–72 Very Severe Cyclonic Storm Tropical Cyclone Severe Tropical Cyclone (3) Typhoon
73–85 Hurricane (2)
86–89 Severe Tropical Cyclone (4) Major Hurricane (3)
90–99 Intense Tropical Cyclone
100–106 Major Hurricane (4)
107-114 Severe Tropical Cyclone (5)
115–119 Very Intense Tropical Cyclone Super Typhoon
>120 Super Cyclonic Storm Major Hurricane (5)

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