2002 GT convertible flooding in back floorboard??

Finally we have gotten some much needed rain here in Austin, however, my car does not seem to like it. This morning when I got in my car I noticed a musky smell and found that the floor behind the driver seat had a pool of water in it... WTF?? is there something up with these convertibles that I should be aware of? I've washed the car a few times and have never even noticed a drop of water inside the car afterwards... and I checked all windows and nothing was cracked...

any ideas???