How cool water eased hurricane Isaac's rage

Caroline Morley, online picture researcher

(Image: National Environmental Satellite, Data, and Information Service)

On the eve of Katrina's seventh anniversary, hurricane Isaac made its first landfall in Louisiana last night. But a period spent over cooler water means it will not follow Katrina's destructive footsteps. On landfall, Isaac was designated as category 1 on the Saffir-Simpson Hurricane Wind Scale.

In August 2005, hurricane Katrina also arrived in Louisiana having travelled across the Gulf of Mexico. It wrought huge devastation in New Orleans. Katrina developed from a category 3 to a category 5 storm when it passed over warm water from the Gulf Stream's Loop Current - the heat of the water intensified the storm. When it hit land, Katrina's intensity fell to category 4 but still managed to cause billions of dollars' worth of damage and kill around 1700 people.

Following a path around the Loop Current and over cooler water means Isaac's sustained winds reached a maximum 130 kilometres per hour compared to the 224 km/h winds of Katrina's landfall. Isaac did spend a short time over a warm eddy in the Gulf of Mexico but then a cool eddy took away the energy it had gained. Still, as a tropical storm Isaac killed 24 in Haiti and five in the Dominican Republic.

Despite being low on the hurricane scale, warnings are still in place for cities in Isaac's path, with many people choosing to evacuate. Slow movement of the hurricane raises the possibility of flooding, says the National Hurricane Center, and there may also be tornadoes as Isaac moves inland.

Source: http://feeds.newscientist.com/c/749/f/10897/s/22db9cbc/l/0L0Snewscientist0N0Cblogs0Cshortsharpscience0C20A120C0A80Ccool0Ewater0Eeases0Eisaacs0Erage0Bhtml0DDCMP0FOTC0Erss0Gnsref0Fonline0Enews/story01.htm

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