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2011 Atlantic Hurricane Season, subtropical, extratropical, tropical storms, difference, unnamed hurricanes, Perfect Storm | The Old Farmer's Almanac

Tropical, Extratropical, Subtropical Storms: What's the Difference?

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NOAA
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Some storms have the potential to develop into hurricanes and others do not. You may have heard weather forecasters talk about a few terms: tropical, subtropical, or extratropical storms. It’s important to know the difference since tropical systems grow quickly grow into hurricanes. Let’s dive in, and you’ll start hearing these terms everywhere!

Powerful storms often appear, disappear and change into each other. This happens most when hurricane season is coming to the end and can get confusing! 

For the most part, there are two types of storms​—tropical and extratropical. Both are created by hot air crashing into cold air.

  • In a tropical storm, the hot air rises from the ocean, hits the cold air and rains out. In an extratropical storm, a cold front hits a warm front and produces rain and wind. 
  • With a tropical storm, the stormiest area is around the central hot spot, the eye. In an extratropical storm, the stormiest area is in the “crash zone” line, where the warm and cold air masses meet.

Sounds simple, doesn’t it?

It gets a bit more complicated. Tropical storms in the Atlantic always become extratropical storms. When they hit land or drift north into cold water the center cools off. The eye disappears. They become a warm front. They become an extratropical storm. 

Then it starts getting weird with another type of storm.

Sometimes a stormy cold front drifts over the hot ocean. Its bottom heats up. Its top remains a normal extratropical front while the bottom starts to act like a tropical storm. This is a subtropical storm, a half and half. If this schizophrenic storm stays in hot water, it can become tropical or even a hurricane.

How subtropical storms are born. Source: Browning Newsletter

This happens a lot at the end of the season. Storms can change as rapidly as a model in a fashion show! 

Ever heard of 1991’s “The Perfect Storm” (also known as “The No-Name Storm” or “The Unnamed Storm”) which has been memorialized in film? It was one of the fiercest storms in history which destroyed hundreds of homes along the Atlantic coast with hurricane-force winds and major flooding.

  1. It started on October 30, 1991. An extratropical cold front became a subtropical storm, which became Hurricane Grace.
  2. It hit another extratropical storm and joined it, creating the disastrous extratropical “Halloween Storm.”
  3. The Halloween storm hit hot water and formed a subtropical storm that became an unnamed hurricane.
  4. The whole mess sank several ships (including the Andrea Gail) and eventually died out as an extratropical storm.

Did you follow this? It wasn’t a Perfect Storm—it was a perfect mess. The end of a hurricane season is always messy.