This. This. 1000 times this. Mappy is spot on.
The general public simply does not process (cannot process?) what that kind of rainfall in a short time over a large area means. I don't know how you overcome that. I think adding to warnings when extreme rain events are imminent that if you live in a basement apartment or lowest level of a structure to be weather aware and have a plan to get higher might be worth considering. I think strengthening the "turn around don't drown" messaging to "do not leave your house and get in a vehicle" in such situations, maybe. 23 dead in cars in NJ and that number is still climbing. I bet most of those didn't drive into flood water, they had flood water appear around their car in areas they likely have never seen flood water.