I've just spent about an hour trying to understand the different steering currents. I get it now.

OK there is undoubtably some stairstepping element to the movement along the ridge of high pressure, but the westward movement is because the high has started moving to the northeast, pivoting around the NW corner of Louisiana (I think in about 12 hours it'll be over Arkansas and Missouri), and has given ground on the west of Rita, so now it is allowing more of a westward movement, but less northward movement.

The interesting thing is, please correct me if I'm wrong, that if Rita stays very strong, the stronger she stays the more of a W movement will occur and the landfall point will go back to SW of Galveston.

Eventually she'll be curving around the SW side of the ridge and moving north along the western side of the ridge, to make landfall.

I'm not sure but it looks like the more she weakens, the more she can edge a little northward in this process?

Note: on the sat wv loop, you can see the convection forming mainly to the south, I am presuming over the eddy of the loop current. Notice in the more recent recons that the temps have gone up. I trhink the completion of the ERC is going to go a lot faster, after some time over these warmer waters, with additional convection. The west movement will allow more time in those waters.