Ike's storm surge about half of what was predicted

Forecasters warned of "certain death," a possible 25-foot surge of water that would wash across the Texas and Louisiana coast, wiping away towns in a white-capped, churning mess of debris.

What Hurricane Ike actually brought was a storm surge about half that, still causing widespread flooding and damage, but far less than the catastrophic predictions.

The experts were "dead on" with their latest forecasts that Ike would come ashore close to Galveston, even as the track shifted over several days, and that it would hit as a strong Category 2 storm, noted National Hurricane Center spokesman and meteorologist Dennis Feltgen.

Yet storm surge size remains one of the most daunting calculations to make, say hurricane forecasters. Ike's maximum surge was about 13.5 feet near the Texas-Louisiana border.

"To get a perfect storm surge forecast, you have to have a perfect forecast for the track, a perfect forecast for its intensity and a perfect forecast of its structure, and we don't know how to do any of those perfectly," said former National Hurricane Center director Max Mayfield.

Benton McGee, supervisory hydrologist at the U.S. Geological Survey's storm surge center in Ruston, La., points to the "many variables."

"There's the size of the storm, which obviously in this case wasn't a good indicator, the speed, the tide cycle, the orientation of the coast, how the hurricane comes in," he said.

Computer models that produce storm surge estimates also aren't perfect, especially with such a large, slow-moving storm as Ike -- nearly 600 miles across, almost as large as Texas.

"Models are based on data, so if you don't have a lot of data, then the model is limited in what it can do," McGee said. "We're really just now putting out enough sensors and enough instruments in the field to really record exactly what's happening."

A storm surge is basically water that is gradually pushed onto shore by the force of the winds circulating in a hurricane. It's similar to a bathtub filling with water while being violently stirred, then overflowing.

Typically, the stronger and bigger a storm and the shallower the coastal slope -- as is the case with Texas and Louisiana -- the bigger the surge will be. But nothing is certain in nature.

"The storm itself changed a little bit. I think it tightened up more, and more of the energy went into the center," stealing some of the punch from the predicted surge, said Wilson Shaffer, chief of the National Weather Service's evaluation division.

McGee also defended the surge estimates as a good call, given how little is known about such massive storms.

"If word went out that this wasn't going to be anything to worry about, and the hurricane changed its nature and strength and it did produce a more significant surge, it would have been a much worse scenario," he said.

No matter how big a surge Ike produced, researchers are still having a hard time comparing it to any other on record, mainly because of its size.

"I don't recall anything similar to this one," Shaffer said.

Ike roared ashore early Saturday at Galveston as a strong Category 2 with 110 mph winds. The only storm researchers can even remotely compare Ike to is 1961's Hurricane Carla, which struck the Texas coast as a Category 4, south of Galveston near Port Lavaca. It had 145 mph winds, producing a Texas record 22-foot storm surge.

Carla remains one of the most powerful storms ever to strike the United States, leaving 34 people dead and causing more than $300 million in damage.

The worst storm in Texas history, and the worst natural disaster ever in the United States, remains a hurricane simply known as The Great Storm of 1900. It hit Galveston dead on, without warning, and killed 6,000 people. More than 3,600 buildings were destroyed by its 16-foot storm surge powered by 150 mph winds.