Many of us are confused by what the ‘sub’ means in front of the word tropical! The difference is laid out nicely below…
Subtropical Depressions and Storms:
- Strongest storms and winds are displaced well away from the center, ~100 miles or so
- Not as symmetrical
- Heavier rain skewed to the east of center
- Not entirely ‘warm core’…meaning it is still deriving energy from the release of potential energy
- Large, cloud free center of circulation
Tropical Depressions and Storms:
- Strongest winds and storms are much closer and compact to center of circulation
- Typically more of a symmetrical wind, rain and cloud field, but not always
- Has an all ‘warm core’…meaning it derives all energy from latent heat release over the warm ocean waters
- Produce more rain
- Needs warm ocean waters, 80° F, to survive and strengthen
Subtropical storms were not named until recently, starting in 2002. Before that, they were just given numbers which is why a lot of people aren’t familiar with the term ‘subtropical.’ There is no such thing as a subtropical hurricane, either. If the system has strengthened that much, it must have become fully tropical.