B777 FLIGHT CREW DECLARES A FUEL EMERGENCY WHEN DIVERSION FROM ZZZZ MUST BE MADE DUE TO WEATHER DELAYS.

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FLT PLANNED ARR FUEL WAS 24482 LBS (1 HR 49 MINS) AND WE ARRIVED AT AIRES THE ARR HOLDING FIX WITH EXACTLY THE PLANNED FUEL OF 26100 LBS. WE HELD FOR ABOUT 30 MINS AS WX APCH THE FIELD FROM THE NW. WE WERE VECTORED ON AND EXTENDED ARR AND ARRIVED ON FINAL EXACTLY WHEN THE SQUALL LINE IMPACTED THE LNDG RWYS. A MICROBURST ALERT WAS ISSUED AND WE INITIATED A GAR. WE ARRIVED AT THE MISSED APCH HOLDING FIX LIBRA WITH 18500 LBS OF FUEL. RESERVE PLUS ALTERNATE FUEL TO ZZZZ WAS 17000 LBS AND WE CALLED DISPATCH AND STATED WE NEEDED TO MAKE A DIVERT DECISION IN 5 MINS. WITH 17500 LBS OF FUEL WE STATED TO TOKYO RADAR THAT WE WERE DIVERTING TO ZZZZ AND REQUESTED A CLRNC. BY THAT TIME 3 OTHER ACFT HAD DECLARED DIVERTING AND SO WE DID NOT RECEIVE A CLRNC UNTIL WE REACHED 16000 LBS OF FUEL. WE DECLARED MINIMUM FUEL BUT WERE HELD AT LOW ALT FOR ABOUT 5 MINS MORE ALTHOUGH WE WERE FINALLY HEADED IN THE CORRECT DIRECTION FOR ZZZZ. OTHER ACFT HAD ALSO DECLARED MINIMUM FUEL. ON OUR CLB OUT TO FL280 WE DECLARED MAYDAY FOR EMER FUEL WHEN WE HAD 8000 LBS. WE WERE THEN GIVEN PRIORITY HANDLING OVER THE MINIMUM FUEL ACFT AND CLRED DIRECT TO ZZZZ. WE LANDED WITH 4600 LBS OF FUEL AND SHUT THE ENGS DOWN WITH 4200 LBS OF FUEL. RESERVE FUEL ON THE FLT PLAN WAS 6059 LBS.