what causes the passenger side floorboard to be wet when it rains

Do you have a moonroof on this vehicle? If so, the moonroof drains could be plugged allowing water to overflow and roll inside the vehicle in various areas. Other than that a body seam is a rare issue, but another big issue -- has the windshield ever been replaced? If so, perhaps some sealer was insufficient causing the leak. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops