Eyewalls may predict hurricane changes

They are looking at a couple of ideas, he said, "but nothing definitive can answer this yet."

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One possibility focuses on the rain bands that move away from the center of the storm, he said. There appears to be a critical distance from the center of a hurricane that they cannot go beyond, and some weather experts think an accumulation of rain bands can form the secondary eyewall.

Another possibility, Houze said, relates to the pattern of humidity. If the storm is very moist in its interior but has lower humidity away from the center, the rain bands may be confined within the humid zone, he said.

High E. Willoughby of Florida International University, who was not part of Houze's team, said in a commentary on the report, "Earth's atmosphere is still fiendishly unpredictable." Developing a way to predict eyewall replacement is crucial to forecasting, he said.

In a separate report, meanwhile, other researchers noted additional evidence that global warming has contributed to stronger hurricanes in the Atlantic Ocean.

The report in Geophysical Research Letters by scientists at the University of Wisconsin-Madison and the government's National Climatic Data Center in Asheville, N.C. added detail to studies last year that found connections between warming and increasingly intense hurricanes.

"The data say that the Atlantic has been trending upward in hurricane intensity quite a bit," said lead researcher James Kossin of Wisconsin. That was not true for other oceans, however.

Sea-surface temperatures may be one reason the Atlantic Ocean is unique, Kossin said. "The average conditions in the Atlantic at any given time are just on the cusp of what it takes for a hurricane to form. So it might be that only a small change in conditions creates a much better chance of having a hurricane."

Both research efforts were funded by the National Science Foundation.

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