Local authorities are already using the Superdome as a shelter for anyone who can't get out of town this evening. I don't know if there is anything else that can be done in this case. Do you think the National Guard has enough manpower and vehicles to evacuate 100,000+ people from New Orleans (on roads that are already clogged with traffic)?
I thought about this earlier. I realized that a huge city like New Orleans probably has hundreds of thousands of schoolchildren riding buses and thousands of busdrivers to transport them. Especially given that school has recently started, the system is in place to transport hundreds of thousands of people.
Had they been ordered to evacuate earlier, they could have executed such a plan instead of simply resorting to sheltering as many people as could fit inside of the superdome and leaving the others that inevitably wont fit to fend for themselves.