Monday, August 20, 2007

Dean gains strength

As Category 4 Hurricane Dean barrels into the Gulf of Mexico, people prepare for the worst.

Dean is rare: only 23 Category 4 or higher hurricanes struck the US mainland since 1851. If Dean should become a category 5, it will only one of 3.

Thirty-eight years ago, engineer Herbert Saffir and U.S. National Hurricane Center Director Bob Simpson came up with the Saffir-Simpson Hurricane Scale to classify Western Hemisphere cyclones into five categories. Hurricanes originating in places other than the Atlantic (and the northern Pacific east of the International Date Line) use different scales.

Saffir-Simpson is based on sustained wind speed: the higher the speed, the greater the potential damage and flooding. It’s interesting to note what Saffir-Simpson does not reflect: specifically location and rainfall. A category 2 storm making a hit over a densely-populated city will be more deadly and costly than a category 5 storm striking an uninhabited area.

In the U.S. sustained wind speed is the average of measurements taken 33 feet above the surface over 1 minute time intervals. By the way, the WMO or World Meteorological Organization uses a 10 minute interval, which means the US will always have higher sustained wind speed stats compared to the WMO.

I guess we’re always striving to be #1, even in hurricanes. And who knows, maybe we’ll even add a Category 6.

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