12z NAM looks pretty close to 6z. According to the NAM the High pressure is not really retreating like we've seen in storms before. It basically provides a NE flow for most of the storm, I mean it takes 12-14 hrs to move from NW PA to NH. Actually the high strengthens from a 1033-1037 over this time period. To me a retreating high would be exiting much faster than whats being shown.