The city will flood. The degree to which it floods is the question. That will be determines by a matter of miles and hours. Where and when it makes landfall seem to be the only mitigating factors. It doesn't appear to be showing signs of weakening, yet. Considering nearly everything built in the last century in Louisiana was "built by Bubba" and the levees and flood gates have never been tested to this magnitude . . . regardless, it won't be pretty.
I remember riding out a storm there in 1978 or 1979, I don't remember exactly when, but it was just a mild storm by hurricane standards and the whole west bank was under two feet of water. The storm sewers just couldn't handle it.
Unless they've done MAJOR renovation to their drainage, they're toast.