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Oceanographers assess effects of inland water on intensity of land-falling hurricanes

Hurricanes quickly lose power when they reach land, yet some retain tropical storm winds and gusts well inland. While studies have shown that the reduction in surface evaporation is one reason for their decay, little is known about the effect of inland surface water on the intensity of hurricanes.

In a recent issue of the Journal of Atmospheric Sciences, URI Graduate School of Oceanography scientist Isaac Ginis and colleagues at the National Oceanographic and Atmospheric Administration studied the effect of inland surface water on hurricane intensity. The team found that under some conditions, the presence of less than two feet of water could noticeably reduce its rate of landfall decay.

Previous studies of land-falling hurricanes used fixed underlying surface conditions. The current study, using a NOAA hurricane model, investigated the effects of inland surface water on land-falling hurricanes, including surface temperature changes and their influence on changes in surface heat, hurricane structure, and intensity. The team of scientists used a range of water depths and surface roughness conditions to correspond to a possible array of surface conditions.

Funded by the National Science Foundation, the study showed that during hurricane landfall over a water-covered land, significant local surface cooling occurs near the hurricane’s core region. This surface cooling causes a reduction in evaporation, the primary energy source for hurricanes, thus considerably reducing hurricane intensity during landfall. The reduction depends on the presence and depth of surface water. With a two-foot layer of surface water the hurricane will maintain its intensity, but it will collapse over dry land.

When a hurricane travels over land, the amount of surface evaporation is considerably less than when it travels over water. However, the scientists found that this condition does not produce major changes in the size of the eye of the storm, even when hurricane intensity is significantly reduced.

Ginis, along with GSO physical oceanographer Lewis Rothstein, developed a computer model to predict the intensity of hurricanes. The GSO model was coupled with a hurricane model created by NOAA’s Geophysical Fluid Dynamics Laboratory to provide a more efficient set of predictors that take into consideration the effects of atmosphere-ocean interactions during storms. The new model results in more accurate predictions of storm intensity. In 2000, the coupled model became an official component of the national hurricane prediction system used to forecast Atlantic and Gulf of Mexico tropical storms and hurricanes.

By Lisa Cugini

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