May 31, 2011

Strong Hurricanes Weaken Before Hitting Gulf Coast

According to new research, cool waters just below the surface of the Gulf of Mexico cause the strongest hurricanes to lose intensity before they hit that part of the U.S. coast, reports USA Today.

The new research could help scientists better predict the storms during this year's hurricane season.

According to the study, published in the Journal of Weather and Forecasting, most of the strongest hurricanes have decreased in intensity just before hitting the Gulf Coast, where two-thirds of all hurricanes hit in the U.S.

As disastrous as it was, "even Hurricane Katrina wasn't as bad as it could have been," study co-author Mark DeMaria of the National Oceanic and Atmospheric Administration (NOAA) said in a statement. 

He said that of the 12 most powerful hurricanes in the Gulf between 1979 and 2008, 10 weakened during the 12 hours before making landfall.

"It's something special about the Gulf of Mexico," DeMaria said in a statement. "In the center of the Gulf, deep, warm water comes out of the tropics, but closer to the northern Gulf Coast, warm water does not extend as deep below the surface."

Hurricanes need warm water to maintain their power, says the study's lead author, Ed Rappaport deputy director of the National Hurricane Center in Miami.

"When hurricanes move over that water, high surface winds tend to mix cooler water up to the surface, which can lessen a storm's intensity," said DeMaria.

The team also found that strong upper-level winds that storms encounter while approaching the Gulf also weaken hurricanes.

The study also found that although stronger hurricanes weaken before making landfall, weaker Gulf hurricanes get stronger before making landfall.  Of the 17 weaker Category 1 and 2 hurricanes studied, 11 strengthened before making landfall.

"This study confirms the perceptions that forecasters have had over the years," Rappaport says.

However, the researchers said not every storm follows these patterns.  Atmospheric and oceanic conditions can combine to allow a strong hurricane to remain strong or even strengthen as it approaches the coast.

Results of the study should have immediate benefits: "National Hurricane Center forecasters can begin applying these results to their forecast process for these important storms right away," Rappaport said.


Image Caption: Hurricane Katrina near peak strength on August 28, 2005. Credit: Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC


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