Um, no. Issac might reach Category 3, but a weaker Category 2 classification in much more likely. The damage from a storm of that strength will be bad, but nothing like that caused by Katrina.
Ike was just a Cat 2 at landfall, but it was huge. Devastation in Galveston. This one is very large, too. We shall see . . .
It might reach Cat 3, it might reasch Cat 5, it might not even become a hurricane. Unfortunately, we don’t have the technology to be very good at forecasting intensity yet. Katrina itself wan’t forecast to be any stronger than a Cat 3 at this point. What scares me about Isaac is his size. If he gets his act together and closes the COC, it could well bomb into a monster... but that may never happen.
Just spoke to a friend in New Orleans who said that if it hits it will be Cat 1.