B747-200 ENCOUNTERED MODERATE-SEVERE TURB IN CRUISE AT FL390.

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GOING FROM NRT-JFK WITH B747-200; AUGMENTED CREW (ME (REGULAR CAPT); FO; SO; IRC). I TOOK LAST BREAK; SO I SAT L SEAT FOR ABOUT THE FIRST 9 HRS. WHEN WE REACHED W COAST OF USA; I QUERIED THROUGH ACARS TO SEE IF THERE WERE ANY TURB ALERTS (TPS) FOR THE USA; AND FOUND SEVERAL; ESPECIALLY ONE FOR PREDICTED MODERATE TURB OVER THE EASTERN PART OF OUR RTE. I NOTIFIED THE LEAD FLT ATTENDANT SO THEY WOULD BE PREPARED. ABOUT 1 HR LATER; I WENT ON BREAK. I WAS ASLEEP IN THE CREW BUNK WHEN WE HIT SEVERE TURB OVER GRB AT FL390. NO ONE WAS HURT; LUCKILY; DUE TO THE FACT THAT WE WERE ALL EXPECTING TURB (ALTHOUGH WE THOUGHT IT WAS ONLY SUPPOSED TO BE MODERATE!). THE IRC; WHO WAS FLYING AT THE TIME; SAID THE ACFT WAS IN SEVERE TURB FOR ABOUT 30-40 SECONDS; AND WAS UNCONTROLLABLE FOR ABOUT 10 SECONDS. WE WERE LUCKY THAT WE THOUGHT TO CHK ACARS FOR THOSE TURB FORECASTS; SINCE THEY ARE NOT AUTOMATICALLY UPLINKED TO FLTS THAT REACH LANDFALL AFTER OVERWATER FLTS OUT OF ACARS RANGE. THEY SHOULD BE AUTOMATIC IN THESE SITS -- THE NEXT CREW MAY BE TIRED AND NOT THINK OF ASKING FOR THEM!