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What is a "subtropical" storm?

Alberto is a subtropical storm as of Saturday afternoon.

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ROANOKE, Va. – Just days before the official start to the Atlantic hurricane season, we have a storm of interest making its way into the Gulf of Mexico. This storm is Alberto, but it's being referred to as a subtropical storm. 

Why is that?

If we think of storms like apples, then we can start to talk about their cores. The core of any storm in this part of the world is usually cold. Tropical storms and hurricanes are different, though, in that their cores are warm. Alberto, as a subtropical storm, has some warm and some cold in its core. 

Here's how this impacts the storm's structure.

By analyzing infrared satellite imagery, we can see that the stronger thunderstorms are far away from the storms center (noted by the red circle). This is also where the strongest wind is located. 

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In a tropical storm or hurricane, the deeper storms and the stronger winds are located very close to the storm's center. In both a tropical or subtropical storm, the maximum winds measured must be 39 mph or greater.

Whether Alberto is tropical or subtropical doesn't really make a difference, though, to those that it impacts. Parts of Florida and the Gulf Coast will see very heavy rain, flooding, high rip tides, isolated tornadoes, and strong wind gusts. 


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