You can see on the attached sat funktop loop the ULL NE of the storm appears to be drawing the mositure away from both Gustav and the tropical wave which has quickly dropped in behind Gustav from the NE.
The NHC is never one to act quickly to name a storm or react after a storm is named. One only needs to look at Hurricane Charley for that intell. I believe between the island of Haiti and the ULL NE of the center of Gustav, he is being torn apart overnight and we'll have to see whats left in the morning.
This loop might not be static.
http://www.ssd.noaa.gov/goes/east/watl/loop-ft.html