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A tropical wave may be headed to Central Texas. Wait, what’s a tropical wave?

A tropical wave may be headed to Central Texas. You may be wondering what that means. Here's an explainer.

What's in a name?

As Invest 91L moves off the Yucatan Peninsula, many questions still exist as to where it is headed and if Central Texas could be a target.

Another question that has been tossed around is how do you define tropical from subtropical and tropical wave from tropical storm? The difference is important since tropical systems usually have the potential to grow rather quickly into hurricanes. On the contrary, extratropical and subtropical storms do not. To understand the differences, you have to examine their origins. So let's get into formation.

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Tropical waves happen way above the surface. Commonly seen as a ripple in the pressure, they are the starter fluid to thunderstorm formation which could eventually lead into tropical development. They form normally in the wake of areas of sinking, dry air. Most notably, they are seen off the coast of Africa which is usually where most of our tropical activity begins for the Atlantic and Pacific basins. They rotate around the south side of an area of high pressure which is the steering factor these storms and can yield widespread showers and thunderstorms, sometimes severe. As the wave moves westward, showers sometimes diminish.

It is important to note that these storms do not carry that signature eye in the center we typically see with tropical storms and hurricanes. Tropical waves can appear very disorganized on satellite and radar imagery.

A tropical depression forms when a low pressure area is accompanied by thunderstorms that produce a circular wind flow with maximum sustained winds below 39 mph. An upgrade to a tropical storm occurs when cyclonic circulation becomes more organized and maximum sustained wind gusts between 39 and 73 mph.

A subtropical storm typically has a large, cloud-free center of circulation, with threatening thunderstorm activity in a band or bands outwards of at least 100 miles from the center. A major difference between tropical and subtropical storms isn't necessarily the winds, but the fact that tropical storms generate more rainfall.

The National Hurricane Center relies on the additional deployment of reconnaissance aircraft missions into these tropical systems to gather data such as pressure, wind speeds and direction to aid in making these classification changes. Surface data from islands, buoys and vessels can also make changes.

Courtesy: http://www.omao.noaa.gov/

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