The fact that it's spreading, probably rules out leftover water from a typhoon or such, but rather water currently entering the cabin.

Only one way I can think of from your desciption (no wash, rain, sleet, snow or hail) and that's condensate from the A/C leaking from disconnected/plugged evaporator box drains. They will leak in the front, but often pool in the back. Not uncommon.

The drains are behind the side covers of the console, near, but not at, the firewall. They empty on either side, by the trans, underneath the car.

I'll bet you have one pulled out of it's little grommet in the console anterior.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)