Hurricane Bertha's Burst of Strength Stumps Experts

Willie Drye
for National Geographic News
July 8, 2008
As powerful Hurricane Bertha churns far out in the Atlantic Ocean, meteorologists are wondering why the storm suddenly gathered strength and escalated from a minimal hurricane to a major one in only a few hours.

By around 3 a.m. EDT Monday, Bertha had barely reached hurricane status with winds of about 75 miles (120 kilometers) an hour.

Forecasters at the National Hurricane Center (NHC) in Miami, Florida, predicted that the storm would not intensify much beyond that.

But 12 hours later Bertha's strongest winds had ramped up to 115 miles (185 kilometers) an hour, making it a Category Three storm and the first major hurricane of the 2008 season.

Earlier Tuesday morning, winds had inched up to 120 miles (193 kilometers) an hour, with the center of the hurricane about 1,035 miles (1,660 kilometers) southeast of Bermuda.

What happened to the storm during those 12 hours is a mystery.

"We haven't come up with any explanations," said Richard Pasch, an NHC hurricane specialist.

"We didn't see anything about the environment that looked particularly conducive [to strengthening] at the time. It just underscores the fact that our forecasting of rapid intensification is not very good."

Not Near Land

Because Bertha is so far out at sea, there are no serious consequences to the hurricane's surprise strengthening.

Had the storm been approaching land, however, the unexpected intensification could have set up a tragedy.

"One … of our nightmare scenarios is a hurricane that intensifies as it's making landfall," said Max Mayfield, a former NHC director who is now a hurricane specialist for WPLG-TV in Miami.

Hurricanes gain strength when they are over water that is at least 80 degrees Fahrenheit (27 degrees Celsius) and there are no upper-level winds, known as wind shear, to disrupt their growth.

Storms that gain intensity very quickly are usually over water that is much warmer than this threshold.

But Bertha was over a region that was barely warm enough to sustain a hurricane, leaving the experts stumped.

Tough to Forecast

Overall, meteorologists have been working for some time to crack the mysteries of rapid storm intensification.

The National Oceanic and Atmospheric Administration has developed a prototype computer program intended to increase the accuracy of intensification forecasting.

"It's a very difficult problem to solve," Mayfield said. "We have to do a better job of observing what goes on in the core of the hurricane."

And conducting such research will take a while, he said.

"I'm a pretty optimistic guy, but it'll be a long time before we make significant improvements in forecasting rapid intensification," he said.

"You can't just collect data here and there and throw it into a computer and expect miracles."

(Related: "Hurricane Felix Forecasts Mostly Failed, Experts Say" [September 5, 2007].)

Hurricane Bertha, meanwhile, has started to weaken and is expected to be back down to a minimal hurricane by Sunday.

The storm is also expected to turn more to the north and remain far from land. As it continues to move, the winds that caused it to head northward will weaken.

"It may meander out there [on the high seas] for days," Mayfield said.

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