Since it happens only when it rains, it would suggest a few possibilities. Look for these:
There are details you didn't give us.If your washroom floor drain only clogs when it rains, that may be a feature, not a bug. There are backflow traps that can be installed in floor drains to keep them from backing up and getting sewer water all over the floor. If your washroom floor is in the basement, the fact that it's clogging when it rains may be saving you from a big, nasty cleanup job.
One reason your floorboard is wet after it rains is that there may be rust holes in the floor or the floor pans are rusted out. A leak in the windshield seal may also be the cause of wet floorboards. Bad door seals or window seals can allow water to soak the floorboards when it rains.
water in distributor cap
windsheild leaks
Windshield seal? Lower door seal? Hole in floor ?
They plant their crops on the floor of the canyon because when it rains the water forms into the sand and canyons and also to collect flood water.
I would check your AC evaporator drain tube , if clogged water will drip on floor.
Water getting into the door and getting the wires wet.
Leaking windshield or clogged windshield cowl drain lines.
haha, I had the same problem. If someone has jacked your car up, they placed the jack in the wrong spot and cracked the body weld. pull your carpet back and seal with some silicone or something like that.
You have a leak. Possibly the drain lines are stopped up or the leak is at the windshield.
There is obviously a leak in either the firewall/cowl area or the window seal.