I’m still trying not to play the blame game, but this is another perspective-point detail: Last summer there was a hurricane worst-case scenario drill for the New Orleans area. See this from CNN.com:

But one of the drill participants, Col. Michael L. Brown, then-deputy director of the Louisiana emergency preparedness department, told the Baton Rouge Advocate newspaper that, in a worst-case scenario, there would be only so much government agencies could do.
“Residents need to know they’ll be on their own for several days in a situation like this,” Brown, who is not related to the FEMA director, told the paper.