The Isaac track continues to veer toward the mouth of the Mississippi and through New Orleans. The US model puts it right on that track. The average of the other models pulls it east, but those are changing. The gulf water is very hot, which could allow quick intensification to a Cat 3 and put Isaac into NO on the most dangerous course by Tuesday night. An orderly evacuation (no one stuck on the freeway going 5 miles an hour for 12 hours) should start more than 48 hours before the storm puts significant rain and wind into the area, which would be Tuesday AM. Just as with every previous storm, including Katrina, Louisiana will wait until it is absolutely certain where the storm is going, then declare a panic evacuation which will either not work, or be nightmarish, or both. This happened with Gustav, and while there was the usual claim that everyone was out of NO, that is always the claim. You do not know until you fill the city with water and count the bodies.
As long as the storm does not come into NO, no one in LA will even question the risk being run. If someone did start the evacuation this morning, and the storm went east of NO, there would be hell to pay over the cost and inconvenience, and, worst, reminding people that NO is at risk.