Watching for changes in the inner eyewall of a hurricane may help forecasters overcome one of the challenges of hurricane predictions - predicting sudden strengthening or weakening. The ability to predict a hurricane path has greatly improved of late, but anticipating changes in intensity has remained a problem.
Now, a research team led by Robert A. Houze, Jr., a University of Washington professor of atmospheric science, is reporting evidence that clouds around the eyewall of a storm can cause sudden changes in intensity.
The findings, in the March 2 issue of the journal Science, are based on analysis of data collected in 2005 during Hurricanes Katrina and Rita. The strongest winds in a hurricane circulate in the cloud wall that surrounds the eye of the storm.
Taking measurements from aircraft flying into these storms, the researchers led by Houze found that occasionally a "moat" of clear air will form outside the eyewall. Winds funneling toward the center of the storm will then form a new eyewall outside the original one, cutting off the storm center from the incoming flow of energy and eliminating the old eyewall.
Because the new eyewall is larger than the old one, its winds circulate more slowly — as an ice skater with arms extended spins more slowly than one with arms held close to the body — thus reducing the intensity of the storm.
But the new eyewall can then begin to contract, spinning faster and faster and increasing the storm's intensity.
[ via The Associated Press ]