Imagine rain falling straight down. Only your hair and your shoulders would get very wet.
This was different.
The wind-driven rain suddenly hit Jody all at once. It hit him everywhere on the front of his body--face, chest, arms, legs. It hit them all at the same instant. All that force suddenly hitting all of that area "hurled him back."
I think "dived" means what U.S. speakers call a "bellywhopper," where the entire front of your body hits the water all at once.