Storm Chris defies NWS forecasts, repeatedly

August 04, 2006|By KEN KAYE | KEN KAYE,SOUTH FLORIDA SUN-SENTINEL

FORT LAUDERDALE, Fla. -- Officials at the National Hurricane Center have long confessed they aren't very good at predicting a storm's intensity.

Tropical Storm Chris confirmed that.

The system once predicted to be a Category 1 hurricane deflated to a tropical blob yesterday. "We've said all along that intensity forecasting is our greatest challenge," said Ed Rappaport, deputy director of the hurricane center, which is in Miami-Dade County. "This points out again that we have a ways to go."

On Monday night, forecasters projected Chris wouldn't even become a tropical storm, yet it did so six hours later.

On Tuesday, they predicted it wouldn't reach hurricane strength, but a hurricane hunter aircraft found it had stronger winds than expected. That prompted a forecast for it to spin into a Category 1 hurricane.

On Wednesday, they still thought it would grow into a healthy 80-mph hurricane, even after a hurricane hunter discovered it was spooling down.

Yesterday, the system all but collapsed and is now expected to limp west toward the Florida Straits as a depression with winds of 35 mph or less.

That is, unless it morphs into a hurricane.

Considering it is moving toward the warm Gulf of Mexico, that remains a remote possibility, said Robbie Berg, a meteorologist with the hurricane center. He added that forecasters would be cautious predicting such a resurrection.

"We don't want to over-forecast that kind of intensity - unless we see that it can strengthen," he said.

The problem for forecasters was that Chris waded into a tricky environment in the western Atlantic, with varying amounts of wind shear and dry air, Rappaport said. That confounded the models and the forecasters.

"Many of the models didn't foresee it developing at all and so failed in that way," he said.

In general, Rappaport said, models don't provide forecasters with much storm-strength guidance to begin with.

Another factor was that Chris had a small circulation, making it vulnerable to even small changes in the atmosphere.

"The storm, when it formed, did so without much of a robust structure," he said. "A slight change in its environment allowed it to get up to tropical storm strength, but other changes weakened it rapidly."

The hurricane center is taking steps to improve intensity forecasts, such as equipping hurricane hunter aircraft with step frequency radiometers, instruments that measure the foaminess of waves around a storm to more accurately determine wind speeds.

But don't expect any major improvements quickly, Rappaport said.

"We understand we need to get better, and we're working in that direction," he said.

Ken Kaye writes for the South Florida Sun-Sentinel.

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