Hurricanes Decoded: How Mother Nature Blows Off Steam


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Hurricane Igor - way too early for Halloween. Image courtesy of NASA

Hurricane Igor – way too early for Halloween. Image courtesy of NASA

The Little Wave that Could

Let’s pretend we’re an easterly wave over Africa. We can’t wait to get out over the Atlantic Ocean, because it’s August and the water temperature will be above 80 degrees for most of our transatlantic trip. We’re licking our chops with the anticipation of spinning up into a hurricane.

Now we’re off the coast, south of the Cape Verde Islands …. but oh-oh, dry air at mid-levels has moved southeast from the Sahara and is in our path. We struggle to survive, and barely make it to the middle of the ocean alive. Here the water is getting warmer and the dry air has been passed by.

We acquire a complete counterclockwise spin; now the weatherman is calling us a tropical depression. The pressure drops in our center and we spin up into a tropical storm, with winds of at least 39 miles per hour. Our thunderstorms are building and we feel confident.

But oh-oh again. West winds at middle and upper levels of the atmosphere are blowing the tops off our thunderstorms. If this keeps up, we’ll just dissipate into a wave again. However, luck is with us. The trough of low pressure that brought the west winds moves north and our vertical structure is intact. We intensify as we pass just north of the Caribbean islands and head for Florida.

The Ultimate Fate of a Hurricane

It’s time for our last oh-oh. We cannot escape now. If we hit the east coast of the United States, the land will quickly cut off our source of energy; but if we turn north into the Atlantic, our strength will be sapped by the colder water. Whether we strike the coast or turn harmlessly out to sea will depend on the strength of a dip in the jet stream, a stream of west winds aloft that circles the globe at mid-latitudes.

Further Reading:

Sirvatka, P. Hurricanes and Tropical Meteorology. College of DuPage. Accessed October 25, 2013.

NOAA. Hurricane Basics. Accessed October 25, 2013.

National Hurricane Center. Hurricane Preparedness. Accessed October 25, 2013.

Weather Underground. Tropical Weather — Easterly Waves. (2010). Accessed October 25, 2013.

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