My first thought is to check the bottom of the door to make sure the drain holes are clear. Checking for a sloshing sound inside the door will help you diagnose if these drains are the issue. Do the same for the rear passenger, in case the issue is there and the water has flowed forward to your feet.
The AC drain would be the alternative thing to check, if the doors are okay. But enough water to slosh around during a rain storm in the middle of October doesn't really sound like the AC drain. It's just a CYA thing to check that might end up saving you a bill from the mechanic.