Tuesday, September 16, 2003

Improvements in the forecasting of hurricanes -

Improved Forecasting Helps Hurricane Experts See Into Storms' Futures
By ANDREW C. REVKIN

As Hurricane Isabel churns toward a probable collision with the Middle Atlantic coast on Thursday, it is providing the first significant test of a new government effort to provide five-day forecasts of hurricane movements.

And federal officials said yesterday that this season's storms had already bolstered recent conclusions that a five-day hurricane forecast is now just as reliable as a three-day forecast was 15 years ago.

Max Mayfield, the director of the National Hurricane Center in Miami, said that the average error range on the 19 five-day forecasts generated since Sept. 6, when the center started issuing advisories on Hurricane Isabel, had errors that were typical of a two-day forecast in his early days at the agency, 30 years ago.

"I don't want to brag about that yet," Mr. Mayfield said, explaining that the hurricane had moved slowly and steadily westward through the tropics and was only now beginning its curving run toward the coast. "Now things get complicated."

The trajectory of the storm is nearly parallel to the Atlantic coast north of the Carolinas, meaning that even a slight tweak to the east could result in a landfall 100 miles or more from the current center of the bull's-eye.

Mr. Mayfield emphasized that people ashore should not be focused on the precise strike zone in any case, because destructive winds swirl concentrically more than 200 miles from the hurricane's eye.

From 1964 until this year, three days was the longest ahead that federal hurricane forecasters dared venture.

In that time, meteorologists greatly improved their ability to predict the track of storms through vastly increased computing power, more realistic simulations of general global weather conditions and increased satellite and aircraft observation of storms' behavior and movements.

But only this year has the National Oceanic and Atmospheric Administration started releasing official forecasts projecting five days of behavior by the lumbering, unpredictable meteorological equivalents of rogue elephants.

Hurricane Isabel has been relatively straightforward as hurricanes go, experts said yesterday, because it is taking a path familiar to meteorologists, in which north-south-running ridges of high pressure constrain a storm's route, just as parallel mountain ranges force road builders to stick to the valleys.

"This storm is in the alley in the Atlantic that the global models just do so well on," said Timothy P. Marchok, a hurricane modeler at N.O.A.A.'s Geophysical Fluid Dynamics Laboratory in Princeton, N.J. Still, it is a sign of the sophistication of modeling and monitoring now that five-day forecasts of Hurricane Isabel generated over the last week, when superimposed, neatly chart the path the storm has actually taken, federal and private meteorologists said.

The latest projections and an archive of earlier ones are at nhc.noaa.gov.

The next big challenge, hurricane experts said, is to improve the ability to forecast changes in a storm's intensity.

"We don't yet understand really what controls storm intensity," said Dr. Kerry A. Emanuel, who analyzes hurricane-ocean interactions at the Massachusetts Institute of Technology. "And the few things we've learned have not yet been incorporated into the models."

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