http://www.ssd.noaa.gov/PS/TROP/DATA/RT/nwatl-wv-loop.html
The 11 p.m. NHC discussion mentioned this feature:
AS A WEAK LOW MOVES
SOUTHEASTWARD FROM THE LOWER MISSISSIPPI VALLEY REGION...THE
MID-TROPOSPHERIC RIDGE TO THE NORTH OF THE HURRICANE IS FORECAST TO
WEAKEN...SO A GRADUAL TURN TOWARD THE NORTHWEST IS PREDICTED.
This could be a key player in the forecast of Ivan, in my opinion. Once it gets to within about 10 degrees of Ivan (it's about 12-15 right now, but closing the gap fast), it should start helping him stall and turn more NW and maybe N. If the trailing trough digs far south enough (not currently forecast to do so, by the way), it could force a sharper turn. It's definitely something to watch.