Kevin Myatt is The Roanoke Times' weather columnist.

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Tropical Storm Gabrielle spun through the Outer Banks of North Carolina on Sunday, but unless you were extremely close to its center, you never would have noticed it.

Some localized areas got heavy rain up to 8 inches in one spot, according to the National Weather Service, but not the widespread torrential rain common with a tropical system. A few places got a gust or two over 40 mph, with the highest reported at 52 mph near Frisco.

When the National Hurricane Center first gave Gabrielle its name, it was known as "Subtropical Storm Gabrielle." You may also remember, back in May, Subtropical Storm Andrea spinning around off the Southeast coast, not far from where Gabrielle developed.

So what is a subtropical storm?

A subtropical storm is a hybrid between a tropical cyclone and an extratropical cyclone -- an extratropical cyclone being what would be more commonly known as a "low-pressure system."

Low-pressure systems are broad areas of rising air that spin counterclockwise (in the Northern Hemisphere; they spin clockwise in the Southern Hemisphere) and form because of large-scale air mass differences.

Put a cold, dry air mass against a warm, moist one, or get some cold air spinning high in the atmosphere above warmer air, and a low-pressure system can develop as warmer air rises, condenses into clouds and precipitation, and is spun by the Earth's rotation.

Tropical cyclones are not fed by atmospheric differences, but entirely by the latent heat of warm ocean water, which is released as water vapor is lifted and condenses into clouds and rain.

Tropical cyclones -- tropical depressions, tropical storms and hurricanes, depending on intensity -- have a very tight, intense core of circulation, with precipitation and wind developing outward from that core as it pulls in air from the outside.

Sometimes, a cyclone will form that has some characteristics of both. Its circulation is broader than that of a tropical cyclone and partly driven by large-scale atmospheric differences, yet it also draws some of its strength from the latent heat of warm ocean water.

That was the case with Gabrielle as it began to spin up between the Southeast U.S. coast and Bermuda early this past weekend.

Gabrielle formed along the remnants of an old cold front -- the same one that moved through and temporarily dropped us back into the 80s to start September. That front washed out in the Atlantic, but a small area of clouds and storms was left behind.

An upper-level low -- a pocket of cold, rotating air aloft -- helped develop a broad circulation Friday, more like a typical surface low-pressure system. Hurricane forecasters, however, also noticed evidence of storm bands arising in patterns similar to that of a tropical cyclone. Once winds above 40 mph were detected, it was declared a subtropical storm and given the next name on the Atlantic tropical list.

Over the next several hours after it was named, the storm developed a stronger, tighter core as thunderstorms kept firing closer to its center. It became more characteristic of a tropical cyclone as it moved over water topping 80 degrees, so the "sub" prefix was dropped and it became Tropical Storm Gabrielle just before landfall.

Subtropical Storm Andrea in May never made the transition to a tropical storm. That was mostly because the ocean just wasn't warm enough, with water temperatures in the low to mid 70s. An ocean temperature of about 80 is considered the baseline for tropical cyclone development.

I've wondered why the National Hurricane Center uses names from its tropical list on subtropical storms.

I found that the hurricane center has been conflicted about this over the years, using different labeling systems for subtropical storms since first recognizing the new category in 1972. It was only in 2002 that the hurricane center finally decided to regularly use names off its tropical list for subtropical storms.

Perhaps Gabrielle has provided the best answer to the question: Any subtropical storm has at least the potential to develop into a tropical storm. And though Gabrielle didn't do so, any subtropical storm that becomes a tropical storm could then also grow into a hurricane.