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Forecasters Still Struggle With Hurricane Predictions

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The Associated Press

Published: August 31, 2008

MIAMI - When a hurricane like Gustav forms, people have two questions for forecasters:

Will it hit me?

And how strong will it be?
Weather experts have become much better at determining where a hurricane will hit, but they acknowledge they have little skill in figuring out its intensity well ahead of time.

With that in mind, government officials must strike a balance between cautioning residents to prepare and not stirring up fear unnecessarily.

That's the challenge with Hurricane Gustav, which has many on edge along the Gulf Coast, including New Orleans and other areas ravaged by Hurricane Katrina in 2005.
Mayor Ray Nagin said New Orleans officials were taking no chances, stepping up their rhetoric to encourage people to get out before ordering them to evacuate.

Forecasts that show Gustav strengthening will only help, he said.

"Once this storm gets in the Gulf of Mexico, and people really see how big and dangerous it is, that's going to help our efforts to encourage people to leave," Nagin said.

In the past two decades, forecasters have reduced their errors in predicting a storm's path by more than half, making it easier to warn the right people and making it more likely they will pay attention.

But over the same time, the accuracy of intensity forecasts is virtually unchanged. Those are off by an average of 25 mph five days in advance, a margin of error that can mean the difference between a low-end Category 1 hurricane and a devastating Category 4. Average error improves to about 12 mph a day in advance.

Scientists have only a limited understanding of how hurricanes form and interact with the atmosphere and the ocean.

That means complex computer models that predict what will happen to them sometimes are based on an incorrect understanding of how the storms work, said David Nolan, an associate professor in meteorology at the University of Miami.

And even with satellites, radar, hurricane planes and observation, researchers have a hard time getting a clear picture of what is happening inside hurricanes.

National Hurricane Center Director Bill Read knows his forecasts can prompt griping from residents who evacuate only to see the storm hit many miles away or fizzle out. But emergency managers often have no choice because forecasts are imperfect.

Read said the government's goal is to cut track errors in half again in the next decade. Improvements in intensity predictions are harder to promise. So are forecasts of a hurricane's size, storm surge flooding and rainfall, which can all influence how deadly a storm is.

"I would be ecstatic if we could, say, correctly forecast half of the time 24 hours in advance a rapid change in intensity, which is the big problem with our errors," he said.

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