B727 FLT CREW ENCOUNTERS HVY RAIN AND WIND DURING LNDG ROLL AND HAS A RWY EXCURSION AT IND.

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FLT TO ZZZ. ATIS RPTING 330 DEGS AT 15 KTS; 10; TS/-RA; 20 FEW 37 OVCST. FO LNDG RWY 32. APCH UNEVENTFUL. HAD RWY IN SIGHT AT APPROX 15 MI OUT; BELOW 3000 FT. ON LNDG ROLLOUT; APPROX 120-130 KTS; AN AREA OF HVY RAIN (A WALL) OCCURRED APPROX 2000 FT DOWN THE RWY REDUCING THE VISIBILITY TO NEAR ZERO AND CAUSED ACFT TO HYDROPLANE TO THE L FROM A WINDSHEAR GUST (OR POSSIBLY A MICROBURST) WHICH APPARENTLY BLEW ACFT NEAR THE L EDGE OF THE RWY. THE CAPT TOOK OVER CTL OF THE ACFT AT THIS TIME. WE COULD NOT TELL AT THAT TIME HOW FAR L THE ACFT TRACK WAS ON THE RWY DUE TO THE FORWARD VISIBILITY AT THAT TIME BEING ZERO FROM THE COCKPIT. ONCE RWY VISIBILITY RETURNED; THE ACFT WAS POSITIONED CORRECTLY DURING THE REMAINDER OF THE LNDG ROLLOUT AND TAXI CLR. IT APPEARED THAT THE ACFT HAD REMAINED ON THE RWY DURING THE LNDG ROLL WITH NO ADVERSE EFFECTS ON THE ACFT. AFTER PARKING AT THE GATE THE MAINT CREW ADVISED US THAT THERE WAS GRASS AND MUD UNDER THE ACFT AND THAT THE ACFT WOULD NEED A GOOD PWR WASHING AND INSPECTION. ALSO; THEY NOTED THAT THERE WERE NO OTHER APPARENT ISSUES OTHER THAN CLEANING WITH THE ACFT. CAPT CALLED ZZZ GND CTL FROM THE CHOCKS REQUESTING A FOD CHK OF RWY 32 AT ZZZ.