At one point I was talking to my friend in Baton Rouge while the rains were just starting there. Boynton was getting rain from the same system - that's a 1,200 mile wide system (just drove it - a crow may do slightly better, but it's a mostly straight shot). Isaac just sat on us for 3 days dumping buckets of rain.
Yes, when the bayous and the lakes all fill up by the second day, and it rains heavy 3 more days, it is just problem on top of problems.