The "Katrina" system extended from the equator to the Arctic Ocean.

The storm was an 'eddy' to a vortex. It maintained it's velocity due to the vortex. The storm was resolving heat induction into the Gulf waters. It so much was 'hooked' into that dynamics that at the latest stages of landfall Katrina skirted along the coast to maintain it's 'water' connection. It finally entered land in Mississippi where the coast was minimally at a higher latitude and there was an entire river Katrina was trying to feed off.