Big Easy Avoids Worst Case Scenario

Waves of computer-model projections and dire warnings of Hurricane Katrina’s path and potential destruction preceded the storm for days, but a slight jog to the north and a little shot of cool air kept the “worst-case scenario” out of New Orleans on Monday.

Katrina went down in the books as the fourth-most-intense Atlantic hurricane in modern times upon reaching its lowest barometric reading of 902 millibars and top sustained winds of more than 160 mph.

But the storm didn’t maintain its catastrophic strength before making landfall 60 miles south of New Orleans, largely because cooler air from another weather system started to influence the storm late Sunday.

Katrina turned course just enough that the low-lying city did not get the storm surge that everyone feared would overwash levees and submerge it under 20 to 30 feet of water.

By last Friday, forecasters at the National Hurricane Center in Miami had nailed their track for the hurricane to within 15 miles of where Katrina ended up going in Louisiana. The typical margin of error is 80 miles. “If that’s not a superb forecast, I don’t know what is,” said Max Mayfield, the center’s director.

But forecasters still can’t be as precise as they’d like when it comes to a hurricane’s intensity at landfall. “We haven’t made the same strides with intensity as the path,” Mayfield said. In fact, Katrina did considerably more damage even as a minimal hurricane at its first U.S. landfall in Florida last week than would normally have been expected.

As the storm headed up the Gulf of Mexico with a growing reputation, researchers at Louisiana State University’s Hurricane Center pumped information from each update into a supercomputer program that projects damage impacts. Under the most dire strength and path projections, Katrina would have damaged half a million homes in southeastern Louisiana, with up to 1 in 4 homes severely damaged or destroyed. The center later reduced that projection by about 200,000 structures after Katrina weakened and moved slightly east.

The New Orleans office of the National Weather Service picked up on the worst-case scenario, issuing a grim forecast Sunday. It warned that if Katrina hit with winds near or above 155 mph, “most of the area will be uninhabitable for weeks, perhaps longer,” and that “at least one-half of well-constructed homes will have roof and wall failure.”

Even President Bush added to the sense of foreboding by joining local and state officials in noting the strength of the storm Sunday evening and urging residents along the coast to move to safe ground.

New Orleans officials said they believe that about 80 percent of residents heeded calls to evacuate, up from about 50 percent when Hurricane Georges threatened to swamp the city in 1998.

“It makes sense that more people would respond to this, given the forecast that people had in front of them all weekend, and a lot of local publicity about how vulnerable the city is to a storm this size,” said Jay Baker, a professor of geography at Florida State University and a leading expert on how citizens behave under hurricane threats.

“We know from our research that a significant number of people in hurricane-prone areas think they’re safer than they really are, so maybe having models and forecasts that spell out the consequences so starkly are a good idea,” Baker said.

“But then again, you have to start evacuating a city like New Orleans so far in advance, I’m not sure how much good it does to scare the heck out of people with dire predictions close to landfall, unless it’s to convince them to go to a shelter of last resort rather than trying to ride it out at home.”

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(Contact Lee Bowman at BowmanL(at)