(Related: "Hurricane Bertha's Burst of Strength Stumps Experts" [July 8, 2008].)
Path of Least Resistance
Gustav is expected to turn toward the U.S. sometime Friday or Saturday, and the high-pressure system will decide how sharp Gustav's turn will be.
"Once it starts moving, it will move west-northwest under the southern periphery of that ridge," said Rebecca Waddlington, a meteorologist at the National Hurricane Center in Miami.
"If the ridge gets stronger, that will keep Gustav moving farther west. If it gets weaker, the storm will move more to the north."
There is "no way of knowing" at present how the high-pressure ridge is going to evolve, Waddlington said. The present long-range forecast says Gustav could come ashore anywhere from the central Florida Panhandle to the Texas-Mexico border.
A hurricane will move along the edge of a high-pressure system until the storm finds a weak spot. Then the hurricane will move toward the weakness as though a door had suddenly opened.
Hurricanes "want to go to the weakest path they can find," said Gary Beeler, a meteorologist at the National Weather Service in Mobile, Alabama, said.
Plenty of Energy
To intensify, storms need water that is at least 80 degrees Fahrenheit (about 27 degrees Celsius). The warmer the water is, the more the hurricane can intensify.
Jeff Garmon, a National Weather Service meteorologist in Mobile, Alabama, said the water temperature in the Caribbean Sea and the Gulf of Mexico is currently as high as 89 degrees Fahrenheit (32 degrees Celsius) in some places.
"There's plenty of potential energy for Gustav to feed off of," Garmon said.
Even if a hurricane has warm water in front of it, however, upper-level winds known as wind shear can disrupt the storm's development and keep it from strengthening.
But wind shear will be very light over the Caribbean and Gulf for the immediate future, and will not impede Gustav's development, Garmon and Waddlington, of the National Hurricane Center, said.
Hard to Predict
There is always uncertainty about the path a hurricane will take, especially longer-term forecasts.
"It's a foregone conclusion that the forecast will have an error in the track," Garmon said. "That's what makes forecasting the intensity so hard." "I'd like to stress that we don't start getting really confident [about landfall location] until it's two or three days out," he said. "That's when you see the whites of its eyes."
"It's not time to panic just yet. But it's time to be aware of what's going on and have a plan in place."
Willie Drye is author of Storm of the Century: the Labor Day hurricane of 1935, published by National Geographic Books.
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