Yesterday I got asked about the difference between tropical, subtropical, and extra-tropical storms, so I thought I would share a little bit of information about the difference between them. The biggest difference has to do with the temperature structure of the storms. Tropical storms are warm-core storms, with warm air centered in the middle of the circulation. Extra-tropical cyclones, which we usually consider our everyday low pressure centers in most of the mid-latitudes, are cold-core storms, with cold air in the center of the circulation. Both are areas of low pressure with winds that rotate counterclockwise in the Northern Hemisphere. Subtropical storms are low pressure areas that have some characteristics of both. The National Weather Service started naming subtropical storms in 2002, so they are not as well-known as the other two types of low pressure. Often tropical storms will transition to extra-tropical lows as they move north and join up with a front or lose their warm core, but occasionally an extra-tropical low can transition to a subtropical or tropical low if it moves over warm water and develops a warm core of air in the center. You can read more about the differences at the links below.
Tropical, subtropical, extratropical?
What is the difference between tropical cyclones and extratropical cyclones?: The Alabama Weather Blog
