HEAVY RAIN AND WINDS DURING LNDG CAUSE RWY EXCURSION.

Narrative

THUNDER SHOWERS WERE RPTED IN THE MCO AREA PRIOR TO OUR ARR. AFTER BEING VECTORED AROUND CELLS AND PLACED ON APPROX 10 MI FINAL FOR RWY 36R; WE WERE CLRED FOR A VISUAL APCH. WE NOTICED A RAIN SHOWER TO THE LEFT OF THE RWY AS WE APCHED. ILS BACK UP WAS USED. THE F/O COMMENTED TO THE CAPT THAT A GO AROUND MAY BE REQUIRED IF THE WX MOVED TOWARD THE RWY. THE WIND WAS RPTED FROM THE W. THE F/O REQUESTED AND RECEIVED MISSED APCH INSTRUCTIONS FROM THE TWR. THE APCH WAS CONTINUED WITH OUR FEELING THAT THE SHOWER WOULD NOT BE OVER THE FIELD PRIOR TO OUR ARR. NORMAL PROCS AND CALLOUTS WERE USED TO 20' AGL WHEN MODERATE TURB WAS ENCOUNTERED. AT OR JUST PRIOR TO T/D; THE VIS BECAME NIL TO NONE (FORWARD) DUE TO THE HEAVY RAIN WHICH ENGULFED THE ACFT. THE WIND BECAME MUCH STRONGER FROM THE LEFT AND I NOTICED THE CAPT WITH FULL CTL INPUT FOR THE WIND AND THE ACFT STILL WX VANED TOWARD THE FAR RIGHT SIDE OF THE RWY. I SAW FROM MY WINDOW BEHIND THE F/O THE POS AND SHOUTED TO STEER THE ACFT TO THE LEFT. THE ACFT WAS THEN CENTERED ON THE RWY AND WE TAXIED TO THE GATE. UPON POST-FLT INSPECTION OF ACFT; GRASS AND MUD WERE SEEN IN THE RIGHT WHEEL WELL. ALSO RIGHT MAIN TIRE. THAT TIRE WAS CHANGED THOUGH IT WAS WELL WITHIN LIMITATIONS AS A PRECAUTION. WE COMPLETED OUR TRIP SERIES WITH NO FURTHER PROBS. RPTS WERE SENT TO OUR COMPANY AS PER OPS MANUAL REQUIREMENT. ANY FURTHER OCCURRENCES OF THIS TYPE OF WX SITUATION WILL BE HANDLED WITH A PRECAUTIONARY GO AROUND AND HOLD UNTIL THE WX IMPROVES.