I think the NHC made themselves very clear in their last forecast discussion on their reasoning behind their forecast...the GFS is the only model according to them that shows any kind of short wave trough moving across the US in the next couple of days. They said since the GFDL and HWRF use the GFS to get their boundary conditions, they may be picking up on this and not truly modeling that situation on their own accord. Until multiple models show this short wave trough, they won't shift their model, and actually the majority of the models in that last spaghetti model that was posted still point towards Houston, only about 4 of them point towards LA.