Thursday, September 4, 2008

Why Hurricane Gustav Didn't Become a Monster

Willie Drye
forNational Geographic News

Hurricane Gustav had the potential to become a monster hurricane last Saturday, but two factors intervened to keep it from intensifying. The hurricane's passage over western Cuba "roughed it up" just enough so that the storm's eye partly deteriorated, said Jeff Masters, director of the private forecasting service Weather Underground in Ann Arbor, Michigan.

And upper-level winds—known as wind shear—were just strong enough to keep the hurricane from quickly regaining power over the very warm waters of the Gulf of Mexico, he said.

The hurricane struck Cuba Saturday with peak winds of about 150 miles (241 kilometers) an hour.

"If the shear had been [a little weaker], it would have survived the crossing of Cuba without undergoing a major disruption," Masters said.

"It would have intensified into a Category 4 hurricane and been a disaster [for the U.S.] We got lucky." (See photos of Gustav barreling into the Gulf.)

Category 4 hurricanes have winds ranging from 131 to 155 miles an hour (211 to 249 kilometers an hour).

Losing Steam

When a disrupted Gustav crossed an area of very warm and deep water in the Gulf of Mexico known as the Loop Current, it was not able to restoke its energy.

Once it was past the Loop Current, Gustav entered cooler, shallower water closer to the Gulf Coast and began losing power.

The hurricane came ashore in Louisiana yesterday morning as a strong Category 2 storm with winds of 110 miles (177 kilometers) an hour.

Gustav was just below the threshold of being classified as a major hurricane with winds of 111 miles (179 kilometers) an hour.

Still, Hurricane Gustav provided a severe test of the repaired levee system in New Orleans.

The storm surges caused water to slosh over the Industrial Canal levee in downtown New Orleans—a levee that failed during disastrous Hurricane Katrina in 2005 but did not break under Gustav.

"That told us that the levee system is improved," Masters said.

But Gustav's power did not fully test the level of protection the levees were designed to provide.

The U.S. Army Corps of Engineers, which has been repairing the levees since Katrina, has said the structures will withstand the storm surge from a Category 3 hurricane.

"They weren't tested to the full level that the Corps has advertised that they've done," Masters said. "We don't know if they will withstand a Category 2 or 3."

(Related: "New Orleans' Rebuilt Levees 'Riddled With Flaws'" [May 6, 2007].)

100 Percent Better

The storm system hugged the Louisiana coast after it made landfall in Cocodrie, a small town on the Gulf Coast about 70 miles (113 kilomters) southwest of New Orleans.

Felix Navejar, a meteorologist at the National Weather Service office in Lake Charles, Louisiana, said southwestern Louisiana fared much better from Gustav than it did three years ago during Hurricane Rita.

Rita was a Category 3 hurricane when it made landfall near the Louisiana-Texas border in September 2005.

"We're 100 percent better than Rita," Navejar said this morning. "It looks really good here—maybe one power outage, but nothing major."

Original here

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