Hahaha. Katrina or not, a Cat 5 hitting SE LA is doomsday for SE LA, coastal Mississippi and SW Alabama. Again. I doubt we'll see Dean with the diameter of any of our big 2005 storms, so maybe the winds won't be 400 miles across. What the GFDL does in the upper levels is what is important for this run to explain why it gets to its conclusion:
What happens is the ULL retrogrades then dives SW into the Gulf opening the avenue for the hit on Louisiana (the other possibility that 500mb hints at is that it kind of falls apart with the fast approach of Dean).
Here's the loop (500mb vorticity):
http://bricker.met.psu.edu/~arnottj/cgi ... =Animation
And the crucial image @ T120:

Steve