Hurricane Ike May Hit Texas With 15-Foot Storm Surge
for National Geographic News
|September 10, 2008|
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.
The water off the coast of Texas is shallow, making the state more vulnerable to strong surges, Masters said.
For instance, an unnamed hurricane that struck Texas in August 1942 was a powerful Category 3 with winds of about 115 miles (185 kilometers) an hour around its center when it was in the Gulf's deeper waters.
A Category 3 would usually create a storm surge of about 9 to 12 feet (2.7 to 3.6) meters.
But the 1942 hurricane weakened considerably before it came ashore about halfway between Houston and Corpus Christi.
Still this hurricane pushed a storm surge of as much as 15 feet (4.6 meters), and much of that surge was caused by the shallower waters of the continental shelf—a likely scenario for Ike, Masters said.
A hurricane of that strength would normally create a storm surge of only about 4 or 5 feet (1.2 or 1.5 meters) as it made landfall.
Ike diminished from a powerful Category 4 to a Category 1 when it made landfall in central Cuba earlier this week. The storm moved into the Gulf of Mexico yesterday. (Watch a video of waves crashing over buildings in Cuba.)
But the hurricane is expected to reenergize as it crosses an area of deep, warm water in the Gulf known as the Loop Current, and may reach Category 4 status with winds of 131 to 155 miles (210 to 249 kilometers) an hour.
Merriman of the National Weather Service said the forecast track for Ike is likely to change before it makes landfall.
It could end up hitting the Texas coast from Port Arthur near the Louisiana border southward to Brownsville near the U.S.-Mexico border.
But regardless of where Ike comes ashore, its storm surge is expected to inundate the low-lying barrier islands just offshore from Texas, experts said.
Willie Drye is author of Storm of the Century: the Labor Day hurricane of 1935, published by National Geographic Books.
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