JACKSONVILLE, Fla. – We are watching a disturbance moving off of the coastline of Florida that has a likely chance to develop into either Subtropical Storm Arthur or Tropical Storm Arthur, here are the main differences between the two.
When it comes to the wind speeds that can be generated, it is the same with subtropical and tropical storms. A subtropical storm may become a tropical storm if it spends enough time over warm water and thunderstorms build up closer to the center of circulation. The transition happens when the heaviest rain and winds are no longer over 100 miles from the center.
Subtropical storms are generally less dense and more spread out than tropical storms. They will still have a well defined center with a closed circulation, but tropical storms see thunderstorms very close to their center, where as subtropical storms see thunderstorms over 100 miles away from the center.
Tropical storms are much more symmetrical than subtropical storms. The subtropical storms do not have evenly distributed winds and rain -- which can sometimes lead to heavier rainfall.
The strongest winds in a tropical storm will be closer to the center, but in a subtropical storm the heaviest winds will be 100+ miles away from the center.
Subtropical storms have a cold core in the upper troposphere instead of warm like tropical storms. They derive a significant proportion of their energy from baroclinic sources.
There is no such thing as a subtropical hurricane, the subtropical storm would first become a tropical storm and then a hurricane.
The Weather Authority Meteorologist Mark Collins weighs in, "Subtropical systems often occur outside the season when the sea surface temperatures are lower than 80 degrees. Fast upper level winds help start the storms which is not the case in tropical storms or hurricanes.
Storms can morph into tropical systems like what happened to Hurricane Gustav in 2002. It was the first Subtropical Storm to receive a name but became tropical shortly after naming.
Subtropical storms were first tracked using numbers when the NHC began naming subtropical systems in 1972."