I'm surprised there's no real mention of the obvious "press-on-itis" that took place here. The weather was dog****e (how useful a ground crew famil in those conditions is another question) and the pilot was confronted by an aerodynamic visibility/precipitation condition he had not previously encountered. So that generates 2 questions:
1. Why not divert to somewhere that wasn't enjoying torrential rain and thunderstorms?
2. If the weather was widespread enough to preclude a meaningful diversion, why even get airborne in the first place?
The reports hits all the technical and technique issues, but there was some basic airmanship and command decision making at fault here around the entire sortie.