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.

[edit] Atlantic and East Pacific

Main article: Saffir-Simpson Hurricane Scale

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]

[edit] 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]

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

[edit] 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]

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]

[edit] 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]

[edit] See also

Tropical cyclones Portal

• Tropical cyclone
• Saffir-Simpson Hurricane Scale

[edit] References

1. ^ Tropical Cyclone Weather Services Program (June 1, 2006). Tropical cyclone definitions (PDF). National Weather Service. Retrieved on November 30, 2006.
2. ^ Federal Emergency Management Agency (2004). Hurricane Glossary of Terms. Retrieved on March 24, 2006. Accessed through the Wayback Machine.
3. ^ ^{a b} Marine Weather Services (November 17, 2006). Marine Forecasts and Warnings. A guide to Australia's marine forecasts and warnings. Bureau of Meteorology. Retrieved on December 4, 2006.
4. ^ http://australiasevereweather.com/cyclones/global_terminology.htm
5. ^ Emergency Management Australia and Bureau of Meteorology (2002). Tropical Cyclone Severity Categories. Surviving Cyclones. Bureau of Meteorology. Retrieved on December 3, 2006.
6. ^ Comparison between strongest gust and suatained winds from Perth Tropical Cyclone Warning Center
7. ^ Comparison between Cyclone Category System and Beaufort Scale from Brisbane Tropical Cyclone Warning Center
8. ^ http://www.ntlib.nt.gov.au/tracy/basic/Met/Warning.html
9. ^ http://www.wmo.ch/web/www/TCP/OperationPlans/TCP-232005.pdf
10. ^ http://www.typhoon.gov.cn/list_tyknown.php?&id=24
11. ^ http://www.typhoon.gov.cn/zhishi2.php
12. ^ http://news.sina.com.cn/o/2006-05-16/06518935033s.shtml
13. ^ http://www.weathercn.com/room/content.jsp?BPS=1&&Id=519
14. ^ http://www.bom.gov.au/catalogue/warnings/WarningsInformation_TC_Ed.shtml#Cat