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Sunday, Sep 23, 2018
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Meteorologists are calling Alberto a ‘subtropical storm.’ What the heck is that?

We’re all waking up to the impacts of Alberto: dreary rain, gusty wind, the reluctant change of Memorial Day plans.

But while the effects are routine for storm-weathering Floridians, the category of storm Alberto falls into is a little less familiar. Meteorologists are calling it a "subtropical storm," not to be confused with the just plain tropical storms we know and dread.

So, what does that mean?

It basically boils down to a difference in what fuels the storms, said National Weather Service meteorologist Andrew McKaughan.

A subtropical storm falls into the category of what he called "extra-tropical systems," which are more like Nor’easters. They’re fed by temperature differences in the atmosphere. Tropical systems, on the other hand, get their energy from warm water.

LIVE COVERAGE: Keep up with the latest on Alberto.

Alberto is a mix of both at this point, McKaughan said, but its humble beginnings were of a subtropical nature. Cooler water temperatures and high wind shear made conditions unfavorable for a tropical system when Alberto formed.

"A lot of times they’re earlier in the season or later in the season," McKaughan said. "Somewhat cooler waters, more non-summer type features are in place that enable the systems to develop."

Alberto could become a tropical storm by the time it’s expected to make landfall Monday night in the northern Gulf coast, but only if it’s deriving its energy strictly from warm waters. It was just getting to the point Sunday morning where the wind shear had decreased and water temperatures were right around 80 degrees, which is typically needed to sustain a tropical system, McKaughan said.

"I’m not sure if it’ll be able to fully transition before it comes to shore, but it’s trying to," he said.

McKaughan compared Alberto to Hurricane Sandy, which led a reverse path. It started as tropical storm, then strengthened to a hurricane before becoming more of a subtropical storm as it moved north. A similar system closer to home was Subtropical Storm Andrea, which kicked off the 2007 hurricane season off the coast of Daytona Beach, also in May.

So that’s the science behind it, but really, it doesn’t matter for how you prepare. Alberto will bring the same rain, wind and flooding we’re used to from tropical storms, McKaughan said.

"As far as the hazards on land are concerned," he said, "it’s really no different."

Contact Kathryn Varn at [email protected] or (727) 893-8913. Follow @kathrynvarn.

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