COMMUTER LTT WRONG RWY LNDG AT ATL IN RAIN.

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RECEIVING A RADAR VECTOR FOR A VISUAL APCH AROUND A TSTM THAT WAS IN THE APCH PATH OF RWY 27L; OTHER RAIN SHOWERS IN IMMEDIATE VICINITY OF APCH END OF RWY 27L AND DEP RWY 27R. WEAK F/O (COMMUTER) FLYING AND NOT AWARE OF RAIN; VECTORING ALT'S; ETC. CAPT TOOK OVER APPROX 2-3 MI FOR RWY ON VECTOR AT 1200' AGL. APCH CTL VERY BUSY. WE LEFT APCH CTL AT 2 MI FROM RWY AND ASKED IF WE WERE CLRED TO LAND. CLRED TO LAND RWY 27. ENTERED RAIN SHAFT TURB; SHEAR; ETC. CAME OUT OF RAIN SHAFT AND SAW RWY TO LEFT CLEARLY. MADE LEFT DSNDING TURN FROM 300-400'; NO TFC ON RWY. RAIN ON BOTH SIDES OF RWY; WHICH WE SAW CLEARLY LIKE A TUNNEL IN A RAIN SHOWER. MADE LNDG AND ON ROLLOUT WE DISCOVERED WE WERE ON RWY 27R; NOT 27L. AN ACR JET EARLIER MADE A GO AROUND. OUR COMPANY AHEAD OF US TOLD THE TWR ACFT SHOULD NOT BE LNDG AS THEY WERE ALSO LINED UP FOR RWY 27R AND THE TWR ASKED THEM IF THEY WANTED TO LAND RWY 27R AND THEY SAID THEY WERE CORRECTING AND WOULD LAND RWY 27L. WE THEN LANDED AFTER THEM CLRED TO LAND RWY 27. TURNING OFF THE RWY TO THE RIGHT I LOOKED BACK AND SAW ANOTHER ACR; VERY LOW OVER THE APCH END OF THE TXWY FOR RWY 27R. MANY PLTS ON THE TXWY CRIED 'PULL UP; GET THAT GUY OUT OF HERE.' I WOULD SUGGEST NO SHORTCUTS FOR VISUAL APCHS WHEN WX IN THE IMMEDIATE AREA IS MARGINAL OR BUILDING (RAIN); TRW'S; WIND SHIFTS. WE SHOULD HAVE USED A BACK UP ILS. WE DID USE THE RADAR ALTIMETER AND MOST OTHER INSTRUMENTS DURING THIS APCH. LIGHTNING MAY HAVE INTERRUPTED THE ILS. ALSO THE ARPT THEN WAS TURNED AROUND AND THEY STARTED TO TKOF AND LAND TO THE E.