Actually, I think this would be the *worst* time for them to hit (from their perspective). Media coverage of their strike would be "competing" for airtime against the Katrina disaster. Furthermore, unless their strike was *massively* huge -- greater than even 9/11 -- it would look like small-potatoes compared to the scope of the Katrina damage (in both lives lost and property destroyed).
Why would the terrorists want to strike at a time which would *lessen* the impact of their attack, and possibly even make it look paltry in comparison? Would the terrorists really want the American public to conclude, "oh well, terrorism sucks, but natural disasters are a bigger threat..."?
Heh, all our emergency response will be in that region (LA/MS/AL). It has already begun to wreak havoc on the oil market... and will soon trickle down to the economy. We are wounded, and no one is paying attention to terrorism right now. UBL/Zawahri already gave us our final warning before the next attack as far as most experts are concerned. IF they have people in wait, this would be a very opportune moment to make a big hit. The key is it would have to be big, but we already saw they seem to focus their biggest on the U.S.
I think you are correct in that the media coverage fuels most terrorist acts, however their main objective is to destroy America. If they were prepared (and that's a big IF, since I think most of their energy is thankfully directed at stopping Iraq from becoming a democratic country), they could seek to further damage the US economy.
If the terrorists have any brain cells at all, they would realize we are in no mood right now to play well with others.