I have a 2004 G35 coupe. Whenever it rains for awhile, and I get into my car, the floor is wet on the driver side right underneath wear my right foot would naturally sit. When it rains very little, it just has a little dribble of water, which helps me pin point exactly where it is coming up, but when it rains a lot, a good square 6 inches is soaked.

Since this is happening when it rains, it is obviously not some other leak other than water...but I don't understand how it's happening.

Has this happened to anybody else? Any advice?

I'll reiterate, it is coming up from the floor, not falling down from above or something...

 

It's not coming from the floor, that's impossible unless you're driving.

You have a leak somewhere else. Use a helper to do a water bath with a hose while you're inside to source the leak.

 

My hypothesis is that it comes in somewhere else, runs along something under the car and then is absorbed by the carpet...

But I definitely will try the water bath idea.

 

I'm with RBull, I doubt it would come from below. Probably a leak around the windshield somewhereand seeping down.

 

try the drainage setup from the engine bay area and see if its leaking from in there and coming in through the firewall

could be coming in through the door sills, windshield seal and running down the A-pillar

but yeah, water doesnt travel up!

 

Check the sunroof drain lines.

This a very common symptom of a plugged drain line.
Drain lines are often route down the A pillars.