Dr. Keith Blackwell, Associate Professor with University of Southern Alabaman's Meteorology Department, says a double eye wall explains the size, destruction and power of Hurricane Katrina.

From Louisiana to the Mississippi/Alabama line, residents in three states were hit twice.

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Meteorologists missed the double eye wall because of older technology it couldn't penetrate this cloudy layer. But with microwave satellite imagery it can. You can see into the storm. And it was this technology used to identify Katrina as having a double eyewall.

Dr. Blackwell believes double eye walls are common with stronger storms. What makes this different: a double eye remained when Katrina made landfall. That doesn't happen too often.

And it's something the Gulf Coast residents will never forget.

News of the double eye wall could shake things up for insurance companies. Many homeowners were told their insurance plans didn't include flood damage. But according to Dr. Blackwell, very strong outer-eyewall winds were on shore hours before significant storm surge came through.

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