HVY RAIN SHOWERS AND ACR MLG RACE TO ARPT. RAIN WINS.

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WE WERE INBOUND TO MSY ARPT; STAYING BUSY DEVIATING AROUND NUMEROUS RAIN SHOWERS. INITIALLY WE PREPARED FOR AN ILS APCH TO RWY 10; BUT THERE WAS A RAIN SHOWER THREATENING TO MAKE THAT CHOICE UNATTRACTIVE. AFTER TALKING TO APCH; WE DECIDED TO TRY AN ILS APCH TO RWY 1. MY THINKING WAS THAT WE COULD BEAT THE RAIN SHOWER BY MOVING AROUND TO THE E OF IT AND LNDG ON RWY 1. WE WERE VECTORED BY APCH CTL AND CLRED TO INTERCEPT THE FINAL APCH AND CLRED FOR THE APCH. MEANWHILE; THE RAIN SHOWER THAT HAD INTERFERED WITH RWY 10 HAD MOVED TO THE E (TOWARDS RWY 1). THE FO AND MYSELF STILL THOUGHT THAT WE WOULD BEAT IT TO THE ARPT. WRONG! WE WERE ESTABLISHED ON THE GS INSIDE THE FINAL APCH FIX WHEN THE TWR RPTED THE RVR ON RWY 1 HAD DECREASED TO 3500 FT. ALTHOUGH THIS WAS BELOW MINIMUMS TO COMMENCE AN APCH; WE WERE LEGAL TO CONTINUE SINCE WE WERE ALREADY ESTABLISHED. SO WE DID CONTINUE. WE HAD A SMOOTH RIDE; ALTHOUGH WE EXPERIENCED MODERATE RAINFALL. WE SAW THE RWY AT DECISION HT AND DECIDED TO LAND. THE RAIN WAS GROWING HEAVIER AS WE TOUCHED DOWN ON THE 7000 FT RWY. I HAD HELD A HIGHER THAN NORMAL APCH SPD IN CASE OF WIND SHEAR. ALTHOUGH WE EXPERIENCED NO WIND SHEAR; THE HIGHER APCH SPD CONTRIBUTED TO AN INTERESTING ROLLOUT ON LNDG. WE GOT THE AIRPLANE STOPPED BY USING ALL OF THE RWY AND REVERSE THRUST RIGHT DOWN UNTIL TAXI SPD. BRAKING ACTION WAS VERY POOR. ALTHOUGH WE WERE LEGAL TO CONTINUE THIS APCH; PRUDENCE SHOULD HAVE DICTATED A MISSED APCH AS THE VISIBILITY DECREASED AND THE RAINFALL INCREASED. HAD WE JUST WAITED 15 MINS; THE WX HAD CLRED COMPLETELY.