The speed at which a hurricane progresses across the ocean may help forecasters predict which areas are at risk from flooding by storm surges.

When hurricanes strike, flooding causes more damage than the wind, and kills more people. To predict the severity of a surge, forecasters tend to rely on factors such as the size and the intensity of the storm. Now Joao Rego and Chunyan Li of Louisiana State University in Baton Rouge have calculated that a hurricane's forward speed influences the peak height and inland "reach" of surges.

The pair fed measurements from 30 sites in Louisiana and Texas hit by hurricane Rita in 2005 into a computer model that relates the severity of a surge to the hurricane's speed of travel. When they raised the speed in their model to the maximum realistic value, the peak of the surge was 7 per cent higher than Rita's, and the volume of water pushed inland fell by up to 40 per cent. This meant areas close to the coast were hit harder, but sites further inland were left unscathed. For the slowest storms, the opposite happened: peak surge was lower, but inland reach increased (Geophysical Research Letters, DOI: link).

"The results emphasise yet again that storm impacts are highly sensitive to factors other than just simply intensity," says Greg Holland of the National Center for Atmospheric Research in Boulder, Colorado.