At least Hurricane Katrina is at the strongest its going be (hopefully) right now. Statistically, its most unlikely that its 175mph winds will hold up right up until landfall... and if any drier air to the north gets entrained into the system, it could weaken some. water vapor loop
The region of strongest winds are some 50 miles across...thats just like an F3 tornado 50 miles in diameter
And hopefully, (for the sake for New Orleans), it will take its northward turn earlier than expected and pass to the east of the city, meaning that the strongest part of the system also avoids them, and the prevailing wind direction will be from the North, backing towards the West as the storm moves inland...ie offfshore, mitigating the effects of the surge. Wherever it hits is going to get severely damaged...lets hope its the least populated area along the Gulf Coast.
I just watched a scary interview on ABC... there are some 100,000+ people who cannot afford, or dont have the means to get out of the New Orleans area, those parts of the city that are below sea-level. The worst case scenario is almost unimaginably horrific... lets just hope that N.O dodges this bullet.