OP, make sure whatever you carry your stuff in is waterproof, then put a change of clothes in it.

should work. but, if it's raining as hard as you say, i'm guessing the rain won't last too long. if it were me, i would keep in mind that people unfamiliar with driving in the rain are freaking crazy drivers when it rains. especially when it rains hard. i'd find a dry place to sit, get some food and a book out of my bag, and i'd wait for it to pass. maybe catch up on a phone call to an old friend, or ... (something other than be on the road with freaked out drivers on oil slicked wet roads)