Tropical vs. Subtropical: Few similarities, many differences

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RALEIGH, N.C. (WNCN) — The Atlantic hurricane season doesn’t officially begin until June 1, but that doesn’t mean we haven’t had tropical activity before the month of June.

Since 2015, a named storm has developed each year before June 1, with one of those being a hurricane (Hurricane Alex in 2016).

As we continue to cross days off the May calendar, we are now looking at a potential disturbance by this weekend.

An area of low pressure is forecast to develop late this week or early this weekend, with the National Hurricane Center giving it a 70 percent (high) chance of development over the next five days.

As we’ll likely be talking about a subtropical depression or storm by the weekend, it’s a good time for a quick refresher on the difference between tropical and subtropical systems.

First, a few similarities. Both are monitored by the National Hurricane Center, and the NHC will issue forecasts and advisories for tropical and subtropical systems. A subtropical depression will be given a number, and a subtropical storm a name, just like their tropical counterparts. Both will also be classified as a storm when the winds are 39 mph or higher.

There are distinct structural differences between the two. For a tropical system, the strongest winds and deepest storms are near the center of circulation.

For a subtropical system, the max winds and deepest storms are found away from the center. Now think of these systems like a cake with layers.

For a tropical depression or storm, each layer will be warm, whereas a subtropical system is warm at the lower levels but cold at the upper levels.

Subtropical storms are almost like a hybrid. It’s why we can see this type of system form in areas where sea surface temperatures are cooler, and even before the hurricane season officially starts.

Whether a system is tropical or subtropical in nature, we can still feel impacts here in central North Carolina.

Make sure your household has a plan in place now, so you’ll be prepared for whatever weather comes our way.

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