Subtropical Cyclone - Characteristics

Characteristics

These storms can have maximum winds extending farther from the center than in a purely tropical cyclone and have no weather fronts linking directly to the center of circulation. 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 similarly to their tropical cousins, based on maximum sustained surface winds. Those with winds below 18 m/s, 65 km/h, 35 knots, or 39 mph are called subtropical depressions, while those at or above this speed are referred to as subtropical storms.

Subtropical cyclones are also more likely than tropical cyclones to form outside of a region's designated hurricane season. Examples include Subtropical Storm Ana (which became Tropical Storm Ana) in late April of the 2003 hurricane season, Subtropical Storm Andrea in early May and Subtropical Storm Olga (which became Tropical Storm Olga) in mid-December of the 2007 Atlantic hurricane season, and Subtropical Storm Beryl (which became Tropical Storm Beryl) in late May of the 2012 hurricane season. Diagrams which depict a cyclone's phase depict subtropical cyclones with a shallow warm core and as asymmetric systems, similar to tropical cyclones which have begun the transition to an extratropical cyclone.