

New tool to help gauge strength of hurricanes


MIAMI -- Most hurricane forecasters are haunted by the same recurring nightmare: Just before a relatively weak storm strikes land, it explodes into a monster, allowing little time to raise the alarm.

That fear will not be put to rest anytime soon, but it might diminish somewhat, thanks to a new radar tool designed to give forecasters a continuous picture of an approaching storm's strength.

Unveiled by researchers Thursday, VORTRAC (Vortex Objective Radar Tracking and Circulation) uses the existing network of 21 coastal Doppler radars, including six in Florida, to create a detailed three-dimensional map of a storm's swirling winds and central barometric pressure, the key indicator of strength.

Unlike reconnaissance planes, which at most fly into a hurricane's eye to measure pressure and other vital data a few times a day, the coastal Dopplers can scan a hurricane's winds as often as every six minutes.

As such, VORTRAC, which was developed by scientists at the National Center for Atmospheric Research and the Naval Research Laboratory, should give forecasters quicker warnings of a storm's sudden intensification -- or weakening -- as it nears the coast.

"This is a watchdog that sets off alarms," said Colin McAdie, a radar expert at the National Hurricane Center west of Miami, where forecasters plan to test VORTRAC during the 2007 hurricane season that begins June 1.

"When the central pressure starts dropping, that is not a good thing because that means the winds will strengthen. So the sooner we know the better."

Had VORTRAC been in use the morning of Aug. 13, 2004, forecasters might have had about an extra 90 minutes' notice that Hurricane Charley was exploding from a Category 2 storm to a Category 4 shortly before pummeling Punta Gorda in Charlotte County, McAdie said.

In Charley's case, though, that likely wouldn't have made much difference.

Wayne Sallade, Charlotte County's director of emergency management, said that wouldn't have been nearly enough time to tell residents who hadn't heeded evacuation orders or boarded up their homes to do anything differently.

Still, Sallade said, VORTRAC has the potential to be revolutionary.

"With 90 minutes, the message would have been the same: Hunker down, get into the closet, stay away from glass and ride this thing out," he said. "But give me 10 hours, and you're talking something. This [VORTRAC] could be a piece of the intensity puzzle, the start of something very significant in hurricane forecasting. We'll see, but it's only the tip of the iceberg."

Though hurricane forecasters have cut errors in their track predictions by half during the past 15 years, they've made negligible gains in predicting rapid changes in intensity.

A big reason: Forecasters don't have the kind of detail they need of how the core of a hurricane interacts with the environment around it to plug into their models.

How much advance notice VORTRAC could provide of an intensifying storm will depend on how close the storm is to land.

In any case, though, the coastal Dopplers can scan a radius of 120 miles, so VORTRAC will work only for hurricanes within that distance.

Scattered along the coast from Texas to Maine, most of the Dopplers are too far apart to provide overlapping coverage, so they measure only the winds blowing toward it or away from it. And that's where VORTRAC comes into the picture.

Using real-time data from the radar closest to an approaching storm and general knowledge of a hurricane's structure, NCAR researchers Wen-Chau Lee and Michael Bell developed mathematical equations that can create three-dimensional maps of the storm's winds and calculate its center pressure.

And, so far, VORTRAC works, at least in retroactive tests. Fed data from Charley, the new tool accurately predicted that deadly hurricane's sudden burst of power, Bell said.

"Since we're getting the data every six minutes, we have a continuous picture of the storm's intensity -- and hopefully ample warning the next time a hurricane rapidly intensifies so close to land," Bell said.

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