Sounds like an evap core leak. Underneath the vehicle somewhere on the firewall should be a length of small diameter tubing. Most are two to three inches long and are bent 90* downward, but I have seen very long ones in the past as well. This is the drain from the evaporator core used by your A/C system. Occasionally these drains get plugged and the condensation has nowhere else to go. If you have access to compressed air, it is easy to use a blowgun and shoot a small burst of air into the drain to clear the obstruction. Otherwise, careful use of a length of mechanics wire will work as well.
I'm always surprised at how much water comes out of these things. Last summer I had a Mitsubishi in the shop and I bet 3 gallons came out