SUB TROPICAL CYCLONES
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. Therefore, 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 than what is observed for purely "tropical" systems. The maximum sustained winds for sub-tropical cyclones have not been observed to be stronger than about 33 m/s (64 kts, 74 mph)).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 has been at least one occurrence of tropical cyclones transforming into a subtropical storm (e.g. Atlantic basin storm 8 in 1973).
Subtropical cyclones in the Atlantic basin are classified by the maximum sustained surface winds:
 | less than 18 m/s (34 kts, 39 mph) - "subtropical depression" |
| greater than or equal to 18 m/s (34 kts, 39 mph) - "subtropical storm" |
Note that while these are not given names, they are warned on and forecasted for by the National Hurricane Center similar to the treatment received by tropical cyclones in the region.