Subtropical cyclones: what's in the name?

The impacts are different compared to pure tropical systems

Hallmarks of subtropical systems are weaker winds compared to pure tropical cyclones, rain extended farther from the center, colder center temperatures and higher wind aloft.

JACKSONVILLE, Fla. – Sure they both spin, call them tropical or subtropical, the names have been used for decades and both have significant differences.

As Subtropical Storm Alberto showed this season, tropical systems can develop outside the hurricane season between June 1st and November 31. 

In fact, subtropical storms have developed outside the hurricane season every year since 2012 with the exception in 2014.

Spinning clouds and wind in low pressure make cyclones across the world. When they happen over the ocean they are classified based on how they develop. Warm water over 80 typically forms pure tropical systems.

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.

The two classifications come with different impacts since heavy rain typically extends farther away from the center of subtropical cyclones and their strength is limited in becoming strong hurricanes.

Eyewalls are also rare due to dry air typically entering subtropical storms.


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