The Power of Katrina

By Quirin Schiermeier (Nature) - September 8, 2005

Katrina was the third most intense storm ever to make landfall in the United States, with a central pressure of 918 millibars. The storm affected an area of about the size of Britain, and the maximum storm surge was 10 metres, recorded in Biloxi, Mississippi.

The intensity of the storm is due partly to this year’s high sea surface temperatures – in early August the Gulf of Mexico was 2 –3 degrees Celsius warmer than usual for the time of year. That led to perfect conditions for the formation of Katrina, and provided the energy that caused such destruction when the storm hit land. Katrina sucked so much heat from the gulf that water temperatures dropped dramatically after it had passed, in some regions from 30 degrees Celsius to 26 degrees Celsius.

Forecasts don’t augur well for the rest of the season. The hurricane risk usually peaks in August and September, and this year has already been exceptional for the number and intensity of storms, according to London-based firm Risk Management Solutions, which models disaster risks for the insurance industry. Sea surface temperatures in the central Atlantic are likely to remain at least 1 degree Celsius above normal until October, according to forecasts by the US National Oceanic and Atmospheric Administration and Colorado State University, so the risk of hurricanes is likely to remain high until then.