What is a sub-tropical cyclone ?
A sub-tropical cyclone is a low-pressure system existing in the tropical or subtropical latitudes (anywhere from the equator to about 50°N) that has characteristics of both tropical cyclones and mid-latitude (or extratropical) cyclones. Many of these cyclones exist in a weak to moderate horizontal temperature gradient region (like mid-latitude cyclones), but also receive much of their energy from convective clouds (like tropical cyclones). Often these storms have a radius of maximum winds which is farther out (on the order of 100-200 km [60-125 miles] from the center) than what is observed for purely tropical systems. Additionally, the maximum sustained winds for sub-tropical cyclones have not been observed to be stronger than about (64 kt (74 mph, 33 m/s). Many times these subtropical storms transform into true tropical cyclones. A recent example is the Atlantic basin’s Hurricane Florence in November 1994 which began as a subtropical cyclone before becoming fully tropical. Note there
