Ok, it's just before 1:30 AM and I can't quite get to sleep yet and it's clear I haven't actually thought this through but I'm going to throw it out there anyway.
My rudimentary understanding of hurricanes tells me that they gather strength from warm waters, high humidity and light winds.
My solution is fairly simple but probably very expensive. Since it's not practical to try and actually cool the water, we could simply try and cool the air in the path of the storm.
Why not create large (but portable) devices that had no other purpose in life than to pump out massive amounts of super cooled air in to the path of storm? It's also possible (due to storm mechanics) that this must be done from behind the storm too which would make the task much safer for all involved.
With cold air being forced across the surface of water where the storm gathers it's 'fuel', the pressure system would be destroyed and the hurricane should dissipate or at least be reduced to a tropical storm.
There are more details to be worked out here and quite a bit of engineering would have to be done. As slow as hurricanes move though, I would think there would be plenty of time to mobilize, load the super coolers on to ships and put them in place. The coolers could be fueled by the plentiful oil supply in the Gulf of Mexico.
Even though the plan is expensive, it's got to be a heck of a lot cheaper than rebuilding New Orleans.
The initial project could be funded by a stupid tax on those who choose to live in the direct path of hurricanes (yes, that means you mom and dad).