Subtropical cyclone
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A subtropical cyclone is a weather system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitude, from the equator to 50°. An extratropical low may develop into a subtropical depression, which can strengthen. A subtropical storm can develop into a hurricane, and there is at least one case of a tropical storm transforming into a subtropical storm. (Generally however, a tropical storm or tropical depression is not called subtropical while it is becoming extratropical, after hitting either land or colder waters.)
These storms can have maximum winds extending further from the center than in a purely tropical cyclone. The maximum recorded wind speed for a subtropical storm is 33 m/s (119 km/h, 65 knots, or 74 mph), also the minimum for a hurricane. In the Atlantic Basin, the United States NOAA classifies subtropical cyclones just as with tropical ones, based on maximum sustained surface winds: below 18m/s, 65km/h, 35 knots, or 39 MPH is a tropical or subtropical depression, and at or above this velocity is a tropical or subtropical storm.
Subtropical cyclones are also somewhat more likely to form outside of a region's designated hurricane season, as was the case with Subtropical Storm Ana (which became Tropical Storm Ana) in mid-April of the 2003 hurricane season.
In 1972, the National Hurricane Center (NHC) designated these storms as neutercanes, but this term was quickly discontinued the following year in 1973. In 2002, the NHC began giving numbers to subtropical depressions and names to subtropical storms from the same sequence as tropical ones. Previously, separate numbers were given to subtropical depressions and were named with that number upon reaching subtropical storm status (that is to say, Subtropical Depression 2 became Subtropical Storm Two, even if S.D. 1 never became S.S. One).
External links
- NOAA FAQ on tropical cyclones (http://www.aoml.noaa.gov/hrd/tcfaq/A5.html).
- USA Today article on subtropical storms (http://www.usatoday.com/weather/hurricane/2003-04-22-subtropical-storms_x.htm).