What Is a Hurricane? [Hurricane Irene]

Every year, about six tropical storms graduate to hurricane status, pummeling the Carribean and Eastern United States. Yes it's a beast of a rain storm, but how does it get that way, and how do weather folks decide when it should be crowned "hurricane?"

A hurricane is a cyclone—a strong, revolving or spiraling storm—in a tropical environment with winds of at least 74 mph (and that's just Category 1). When low pressure, thunderstorms, and counterclockwise (in the Northern hemisphere) wind circulation all comes together, you get yourself a hurricane. And that means violent winds, incredible waves, torrential rains, and floods. From Texas to Maine, 50 to 100 people die at the hands of a hurricane in an average 3-year period. It's also only called a hurricane if it happens in the Atlantic, Gulf of Mexico, and the Caribbean. In the Pacific, they're typhoons, and in the Indian Ocean, they're cyclones.

The initial rotation is fueled by rising air over tropical oceans near the equator. They need moisture and heat to get going, and late summer is when it's wet and hot. Easterly winds in the upper atmosphere carry the storms westward. Sometimes they recurve toward the pole, but not always, which makes landfall forecasting difficult.

The severity of a cyclone is classified using the Saffir-Simpson scale, which measures wind speed, central pressure, and other scary things associated with hurricanes. The numbers 1-5 indicate the type of damage you should expect: minimal, moderate, extensive, extreme, or catastrophic. How does one decide where to draw the line between extreme and catastrophic? Even experts admit that it's pretty subjective.

But that might just be because nowadays we're bombarded by the second with information about a storm's every move. Whether we're having more and stronger storms than in the past is hotly debated by weather nerds. Storms might just seem worse because in the past we didn't have the fancy tools we have today to measure hurricane info. But there's also the climate change. Scientists don't know for sure if it's making hurricanes worse. But they do know that damage and loss at the hands of hurricanes in the United States are increasing—although that's partly because more people who apparently think they're stronger than hurricanes build stuff near and live along coastlines.

Hurricanes used to be named after the particular saint's day that the storm fell near (Santa Ana, San Felipe), but they ended up with more than one with the same name and it got confusing. They also tried women's names, but that was sexist. Or did it mean women were powerful? In any case, in 1979, the National Oceanic and Atmospheric Administration started a list of alternating men's and women's names.

Watch out for Beryl in 2012. She's sure to be a doozy.

[Jerry Mitchell]

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