Flash flood safety PSA:
Pick the route with construction.
Not only is it possible that the route with construction will actually force you to drive through the deepest waters on the road, but if you want to turn around, tough cookies, there's no escape.
Lesson learned. Luckily everything turned out fine yesterday. Still was quite a nerve wracking drive for quite some time. And with the bonus that, I chose that route. The flooding may have been just as bad elsewhere, but at least, I would've had the option to turn around.