….could not be more different, regarding dewpoints.

The reason may be because the NAM develops some sort of mesolow over the Yucatan Peninsula, which induces some weak northerly surface flow over the Bay of Campeche. The GFS may also be overdoing the dewpoints just a tad; veered low level flow may mix some dry air down to the surface (although, again, the NAM is overdoing it just a bit, IMHO, not to mention it is complete trash 84 hr out).

This post ties into the the severe threat next Monday in the Lower Mississippi Valley, which will be discussed in the coming days.