If a Cat 4 or 5 hit the city from the current trajectory, and assuming everyone in the city was evacuated who could evacuate- there would still be an estimated 25,000 to 80,000 deaths inside the City of New Orleans. Two thirds of the city would be completely destroyed. The immediate damage would be $100-$250 billion dollars. It would take nine weeks just to drain the city, unless they decided to destroy the levees to let the water out.
Around ten percent of the nation's petroleum supply would be disrupted.
The Red Cross no longer pre-places personell inside the city of New Orleans during hurricanes. They believe the risk to them is too great. The Weather Channel isn't even sending in Jim Cantore.
The New Orleans paper has a series of articles about this:
http://www.nola.com/hurricane/?/washingaway/ You don't have to register, but you do have to answer the questions.