If you watch the model runs in a time loop, you'll see where an area of high pressure centered over Florida erodes and Gustav makes his right turn. I still believe between to Atchafalaya basin and Pensacola are at the greatest risk.
It is normal for models to do the windshield wiper - left, then right, then back left. What's important is that they stay within 100 miles or so from their previous runs. That's when you can tell that the model has a good grasp of atmospheric conditions. The GFDL gets a lot of respect from the NHC, it usually performs pretty well.
Also, discount 06Z and 18Z model runs, they use input from the 00Z and 12Z runs and are not quite as accurate. You'll practically never see the NHC base anything off of the 06Z or 18Z model runs.