Yeah once Lan developed, much of the divergence went away in NWP... Now it's going to be more of an issue related to how they handle it's diabatic heating and concomitant upper level outflow as well as the extravagance of the eventual extratropical transition. This ultimately determines the strength of the upper level ridge that will balloon to its NE and the associated ageostrophic geopotential flux that allows the Rossby Wave packet to propagate eastward and thus affects the speed of said Wave packet, timing, amplitude, & shape of the trough over the eastern US around Oct 26...