IN AN EFFORT TO AVOID HAZARDOUS WX ON LNDG; A RWY CHANGE IS REQUESTED AND GRANTED. DURING THE FLARE ON THE NEW RWY WINDSHEAR IS ENCOUNTERED AND A MORE FIRM THAN NORMAL LNDG RESULTED.

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OUR FLT WAS BEING VECTORED FOR A SHORT TURN FOR VISUAL RWY 9L AT MIA. I NOTED A 5 NM DIAMETER CELL ON RADAR AT THE FINAL APCH FIX TO RWY 9L AND OPTED FOR VECTORS TO RWY 12 INSTEAD. I WAS HIGH ON THE GS FOR RWY 12 DUE TO THE SHORT TURN DURING THE DSCNT WHICH WAS BEING PLANNED FOR RWY 9L. WIND SHOWED OUT OF THE E AT 1200 FT MSL AS MAX DRAG CONFIGN WAS DEPLOYED TO GET DOWN TO THE GS. ALL WAS WELL ESTABLISHED AT 500 FT AGL ON ILS RWY 12. MANY PWR CHANGES WERE REQUIRED TO MAINTAIN GLIDE PATH AS WELL AS FREQUENT HEADING CORRECTIONS TO HOLD THE LOC. SPD WAS 140 KTS APPROX REF +10 KTS. AT 40 FT AGL; I FELT THE ACFT SINK AND FO NOTED AIRSPD IMMEDIATELY DROP 10 KTS BELOW REF; A 20 DECREASE IN PERFORMANCE. I ADDED LOTS OF PWR TO ABOUT 1.7 EPR; BUT ACFT TOUCHED DOWN IN A NORMAL LNDG ATTITUDE; BUT HARDER THAN NORMAL. PWR REDUCTION WAS NOT RAPID AS ACFT BOUNCED. SPOILERS EXTENDED AND RETRACTED; WHICH PROMPTED FO TO PULL SPOILER HANDLE AFT. IN AN EFFORT TO SMOOTH OUT THE 2ND TOUCHDOWN FROM ABOUT 8 FT; PWR WAS ADDED AND A SLIGHT SKIP WAS THE N EFFECT TO A SMOOTH LNDG. WINDSHEAR WAS RPTED TO MIA TWR TO CAUTION FOR THE HAZARD OF DECREASING PERFORMANCE AT OR NEAR TOUCHDOWN.