The Problems:

The problem in parts of Louisiana that the Cajun Navy is rescuing people by water like in Jean Lafitte and Houma, Louisiana is that people who spent the night in their attics or sleeping on their kitchen island because their homes were flooded and were picked up in various kinds of air boats of the Cajun Navy (fan boats with flat bottoms which are low water boats or other kinds of boats) but the problem now becomes that the microwave towers and power is gone. So, when they are dropping off people on dry land there is no way to communicate with their friends and relatives to come pick them up. 

The problem in places like New Orleans is that there is no power because of power poles coming down and blowing up transformers and the like. So, food is going bad all over southern Louisiana with no power, no cell phones, no water to drink because sewage got loose in various places, no electricity, no wifi, nothing. So, if people can they are leaving because it is too hot indoors to stay there without electricity and air conditioning and all the food is spoiling and nowhere to go to the bathroom because water isn't working either. So, this is also a sanitary problem because when people have to go they have to go no matter the other conditions

And it could stay this way in many places for weeks or months. So, the best course of action for most people is to leave to where things are better for awhile so they don't wind up getting sick and dying in these conditions. 

Also, they were saying many tourists got trapped in the French Quarter of New Orleans which is a tourist attraction and missed their planes when the hurricane hit and couldn't get out. So, they now too are trying to find rental cars, buses or planes (if any airports are even open at all) to get out too because there is no electricity and it is too hot to be indoors anymore with no toilets working, no water, no electricity, no cell phones etc.

So, it seems like a whole lot of people without communication at the very least might not survive this or survive very well the way things presently are there in Southern Louisiana.