Most of that slightly moister air is just that which has been moved into the region by the upper-level flow from old thunderstorm complexes to the west and from the daytime hours. You'll likely see the ridge "look drier" tomorrow morning; trust me, this ridge is pretty strong and not weakening in the least. As Rita moves a little further to the west, you'll see it start to accelerate some under the influence of the ridge. The thing that you see to "break" the ridge is a trough exiting the east coast of the US, largely the same one that got Ophelia yesterday. However, this trough will likely begin to lift out through time; it'll leave enough of a weakness to keep Philippe from turning back to the west during the forecast period, but should have little impact on Rita's track.