rain in on (someone or something)
Of rain, to cause someone or something to become wet by coming in through an opening of some kind. It started raining in on us through the hole in the ceiling last night. Someone left the skylight in the garage open and it rained in on my brand new convertible.
rain in on someone or something
[for rain] to enter a window or other opening and get someone or something wet. Carol left the window open, and it rained in on her in the night. The storm rained in on my carpet!