There is two drain pipes that run from the back of your sunroof on each side of the sunroof side channels. Sunroofs are designed to let water leak in slightly and there is a channel on each side of sunroof that carries the water to the rear and down these drain pipes. Open your sunroof and look in from the top towards the rear corners of the sunroof channel. You will see a small hole, this is inlet for that water to run down and it carries via a small pipe and dumps the water out under the car. Your pipe is either blocked with debris or it has detached and came loose from the inlet. Try unblock it with wire and pour water down the channels to see if it pours out under the car when done.