for National Geographic News
Shallow waters on the Gulf of Mexico's continental shelf could worsen Hurricane Ike's impact as it heads for the coast of Texas later this week.
Ike's storm surge will increase as it passes from deeper water onto an underwater plateau near Texas, said Jeff Masters, director of the commercial forecasting service Weather Underground.
As of Wednesday afternoon, forecasters predict that Ike's center will come ashore as a powerful Category 3—with winds of 111 to 130 miles (179 to 209 kilometers) an hour—on late Friday or early Saturday.
It's expected to hit near Rockport, a small fishing town about 30 miles (48 kilometers) northeast of Corpus Christi.
"No matter where the center makes landfall, a significant portion of the Texas coast will be affected," said Tony Merriman, a meteorologist at the National Weather Service office in Corpus Christi.
"There will be storm surge, coastal flooding, tornadoes in the northeast quadrant of the storm, and high winds. We're really getting prepared for the worst and hoping for the best," he said.
Earth's continents have an underwater shelf that extends outward from their coasts. Water depth over each shelf varies, as does the distance the shelf extends into the oceans.
The water over the shelves is often shallower than 500 feet (152 meters).
A hurricane's rotation creates a whirlpool effect with water around the storm's center.
Deeper water can absorb the energy of that swirling water around the storm's center so that water can flow down, dissipate, and recirculate to the surface, Weather Underground's Masters said. Because of this, a storm surge doesn't rise as high when a hurricane is over deep water.
But when the hurricane reaches a shelf, the water being forced down has nowhere to go, and that causes the water near the center to rise higher.
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