Gustav Now Major Hurricane -- And Picking Up Steam

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(Special report: National Geographic magazine on New Orleans' hurricane vulnerabilities—full article, interactive map, videos, and more.)

Frightening Leap Expected

Forecasters think Gustav will lose some of its strength as it approaches the Gulf Coast on Monday.

On Saturday afternoon, however, Gustav was already undergoing a frightening leap in intensity, even though it hadn't yet reached the Gulf of Mexico, whose vast stretches of warm water can supercharge storms.

Its in bathtub-warm water now, and its exploding, said Keith Blackwell, a meteorologist at the University of South Alabamas Coastal Weather Research Center.

Soon Gustav will likely reach Category 5 intensity, with winds exceeding 155 miles (249 kilometers) an hour, Blackwell said.

The Loop Current is expected to fuel that intensification. The current is an eddy of very deep, very warm water that moves north from the Caribbean Sea into the eastern Gulf of Mexico before turning southeast and exiting the Gulf via the Straits of Florida (map).

Hurricanes draw energy from water that has been heated to at least 80 degrees Fahrenheit (27 Celsius). The water Gustav will be crossing for the next two days is nearly 90 degrees Fahrenheit (32 Celsius).

The hurricanes strengthening will be aided by the fact that the warm water in the Loop Current goes down several hundred feet. This means that—instead of churning up cooler water that would cause the hurricane to weaken—Gustav will be pulling up warm water, which will further intensify the storm.

Some Weakening Before Gulf Coast Hit

Blackwell and other forecasters think Gustav will lose at least some of its fearsome power as it draws closer to the Gulf Coast.

For one thing, the water closer to shore will be a little cooler. For another, the storm will come under the influence of wind shear—changes in upper-level wind speed or direction—which will disrupt the hurricane and cause it to weaken, the forecasters say.

Furthermore, if tropical storm Hanna strengthens enough, it could push Gustav back into the Gulf of Mexico after the hurricane has made landfall, Blackwell said. On Saturday afternoon, Hanna was in the Atlantic Ocean north of Puerto Rico and moving west toward the Bahamas.

Hurricane Gustav began Monday as a tropical depression in the eastern Caribbean Sea. It quickly strengthened to a hurricane, then weakened into a tropical storm after crossing mountainous Haiti and the Dominican Republic. Gustav later regained intensity after it met open water again.

The storm may have killed nearly 70 people in its trek across the Caribbean.

Willie Drye is author of Storm of the Century: the Labor Day hurricane of 1935, published by National Geographic Books.

HURRICANE BASICS

Hurricane Facts
Hurricane Safety Tips
Hurricane Photos
New Orleans' Faulty Levees (National Geographic Magazine)
Forecasting Killer Hurricanes (National Geographic Magazine)

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