firewall leaks when raining
if you go into your local dealership, it should be an easy fix- something is plugged up and needs to be cleared out.
Couple of things can cause this, Clogged a/c - heater core box drain. Also, possible defective lower windshield seal - this means windshield may have to be removed to repair this. There is also a possiblilty of the firewall seal itself being bad and the drain for the area between the lower windshield - firewall area clogged. Do you park the vehicle where a lot of debris can get into these area? Things such as moss, small tree leaves etc.? If so, the firewall drain is a good bet to be the problem - unless the vehicle has been wrecked on either side or front and not properly repaired.