A B757 CREW; O APCH TO FLL; USED CAPT'S EMER AUTH TO CIRCUMNAV TSTM ACTIVITY ON FINAL.

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WHILE INBOUND TO FLL ON AUG/WED/02; WE WERE SWITCHED FROM OUR FORTL 4 ARR TO THE DVALL 1 ARR FOR THE ILS RWY 27R APCH AT FLL. ON FIRST CONTACT WITH THE FINAL CTLR; WE WERE AT 3000 FT MSL. WE ASKED FOR VECTORS TO LEAVE THE APCH PRIOR TO JUMAR DUE TO A WX BUILD-UP ON OUR RADAR RETURN WHICH WAS IMMEDIATELY W OF JUMAR. THIS WAS WELL COMMUNICATED AND COORDINATED WITH THE CTLR. WE WERE VECTORED N; THEN E; THEN SW. ON THE SECOND ATTEMPT; WE WERE DSNDED TO 2000 FT. THE WX BTWN JUMAR AND SNAPE WAS A TEXTBOOK EXAMPLE OF A MICROBURST -- HVY RAIN COULD BE SEEN FALLING VERTLY ONTO THE OCEAN SURFACE AND WAVES WERE RIPPLING OUTWARD FROM THE CORE OF THE RAIN SHAFT'S IMPACT POINT. OUR VECTORING GAVE US NO OPTION BUT TO GO STRAIGHT -- A R TURN WOULD PUT US INTO THE MICROBURST; A L TURN WOULD HAVE PUT US NOSE-TO-NOSE WITH INCOMING ACFT ON THE SAME APCH. THE FINAL CTLR INSISTED WE EITHER TURN R OR DECLARE AN EMER. CAPT'S RESPONSE WAS; 'IF IT TAKES AN EMER TO PREVENT HAVING TO MAKE A R TURN THAT IS WHAT WE WILL DO.' WE CONTINUED SW. IT DID NOT TAKE VERY LONG TO FLY BEYOND THE MICROBURST AND GET VISUAL CONTACT WITH FLL AND RWY 27R. THE FINAL CTLR WAS VERY BUSY TALKING WITH OTHER ACFT. THE ACFT THAT WAS FOLLOWING BEHIND US SAID 'THAT WX LOOKS NASTY AND NO ONE SHOULD FLY THROUGH IT.' WE INTERCEPTED THE ILS LOC COURSE E OF SNAPE AND CONTACTED FLL TWR FOR A VISUAL APCH TO RWY 27R. THE REMAINDER OF THE 'NOW' VISUAL APCH WAS UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 558436: WHEN GIVEN THE FINAL VECTOR TO INTERCEPT THE ILS APCH TO RWY 27R AT FLL WE WERE UNABLE TO JOIN THE LOC DUE TO A TSTM ON THE LOC COURSE AT JUMAR INTXN. DUE TO THE VECTOR WE HAD NO OTHER OPTION BUT TO DEVIATE TO THE S OF THE LOC APPROX 3-4 MI TO AVOID THE TSTM. THE CTLR SAID TO DO THIS WE WOULD HAVE TO DECLARE AN EMER; SO WE DID.