Agreed that stair stepping is probably going on. The edge of the ridge has permutations in it - however, looks to be about 290-300 deg the last 5-6 hrs while the NHC forecasted path is close to 275. The 5 PM NHC forecast has Rita cross 25N at 90W. Based on my crude approximation, if the last 5-6 hours path continues, Rita will cross 25N at 87.5 W - a full 2.5 deg long difference! There is a weakness in the upper ridge currently over the FL panhandle - I can't imagine that this would be affecting the storms recent motion - she seems to have slowed somewhat also.

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8dlm6Z.html

http://www.ssd.noaa.gov/PS/TROP/DATA/RT/float-ir4-loop.html