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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