Dprog/Dt of the last 5 runs of the GFS showing the slowing trend near+after landfall as #Sally approaches the central Gulf Coast. This is likely due to Sally being stronger and therefore having a stronger westerly component of steering flow (aloft), counteracting the LL SE flow

A stronger storm would have deeper convection, extending higher up into the troposphere, which means that the net motion of Sally would have an increasing component towards the east, with westerly mid-to upper level winds.

This means:

1. A slowing/stalled storm increases the potential for widespread flash flooding due to rainfall+may also increase duration of storm surge.

2. A slowing storm means that #Sally will have more time over water, therefore giving it more time to organize and intensify.

GIF from @TropicalTidbits