THE AIRPLANE HYDROPLANED AFTER LANDING AND RAN OFF THE END OF THE RUNWAY. RUNWAY INSPECTION REVEALED THAT THE RUNWAY GROOVING ALONG THE AIRPLANE'S LANDING ROLL TRACK WAS WORN TO THE POINT TO WHICH IT WAS NONEXISTENT, AND THERE WERE LARGE AREAS OF STANDING WATER ON THE RUNWAY. THE AIRPORT HAD RECORDED 1.28 INCHES OF RAINFALL DURING THE FOUR HOUR PERIOD IMMEDIATELY PRECEDING THE INCIDENT.