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Hurricane Isaac storm surge reversed flow of Mississippi River

Hurricane Isaac was only a Category 1, but its storm surge and slow pace led to inland flooding and reversed the Mississippi for 24 hours. Scientists are working to better forecast these effects. 

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The project is still about a decade away from turning the tool over to forecasters, she says. Among the steps along the way, the team would like to set up a second prototype in a different geographic setting – perhaps along the Gulf Coast.

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Other researchers are looking at the potential vulnerabilities of counties deep inland.

Isaac is forecast to bring heavy rain into the Ohio River Valley and the central Appalachians, according to the National Hydrometeorological Prediction Center in Camp Springs, Md. Isaac's remnants could drop three to five inches of rain along its path, with some locations receiving up to eight inches. Initially, the rain could get a warm welcome from soils desiccated by drought, reducing the initial risk of flash floods, forecasters say. But that risk could increase as the ground becomes saturated.

Purdue University graduate student Dereka Carroll has developed a county-by-county map of the continental US and rated each county for potential tropical-cyclone flood risk. The data include not only meteorological and geographic elements, but also social factors such as income and education levels.

Some of the counties facing the highest potential risk are in Arkansas, largely because of a relatively high level of poverty and poor education in many areas, says James Done, a researcher at the National Center for Atmospheric Research in Boulder, Colo., who is guiding the work. Texas counties stretching along the Rio Grande River are also ranked as high risk because of the large Spanish-speaking population. For now, there are uncertainties about how well hazard information is communicated to and among the US Spanish-speaking population.

The next step, Dr. Done says, is to begin the field work in the high-risk counties to refine the rating. Ultimately, the team hopes to provide a continuously updated map that can help local emergency planners more effectively increase their communities' resilience to tropical cyclones.

For its part, the National Hurricane Center in Miami is working on ways to provide surge warnings independent of any tropical cyclone watches and warnings, according to center spokesman Dennis Feltgen.

Although the center issues advisories that include storm-surge information, many people still tend to focus on wind speeds. As a Category 1 storm with maximum sustained winds of about 80 miles an hour, Isaac was a low-end hurricane. But its large size and slow movement contributed to coastal surges as high as 15 feet.

In addition, surge from a tropical cyclone can inflict damage on coastal areas well outside formal storm watch or warning areas, he explains.

The hope is that breaking storm surge out as a separate forecast will help focus more attention on this related but separate threat.


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