I used to live in New Orleans (attended Tulane University); I saw what the moving water from the Industrial Canal did to the Lower Ninth Ward in person. The exact thing that came to mind for me too was an F5 tornado. The pictures shown by the media were dramatic, but they didn't quite show just how bad it was- they shot footage as they drove of heaps of rubble where houses had been. But when I first saw it, it was a more or less homogeneous and flat debris field; in some places I could not tell where the streets were. Many of those rubble piles they filmed weren't the collapsed remains of houses— they were the piles of debris made by the bulldozers that had cleared the streets they were driving their news vans down.
The Lower Ninth after the flood— F5 just about sums it up.
Those pics of F5 tornado-esque damage may well be of flood and not wind damage. Moving water is capable of some pretty nasty stuff (I saw cars stuck in two separate old Live Oaks in the Ninth too). And while I'm sure the storm surge driven inland by Nargis wasn't moving as fast as the water from the breach in the Industrial Canal, I'm also sure that waves driven in 130mph winds must be capable of some pretty spectacular damage on their own.