A B747-400 FLIGHT CREW DECLARED AN EMERGENCY AND DEVIATED FROM THEIR ASSIGNED COURSE OVER THE PACIFIC WHEN THEY ENCOUNTERED THUNDERSTORMS AND COULD NOT GET A CLEARANCE.

Narrative

AFTER LOGGING ON CPDLC TO RJJJ WE ENCOUNTERED A TWRING CUMULO NIMBUS ON OUR RTE. I REQUESTED DEV L12. THE RESPONSE WAS 'STANDBY.' 2 MINS LATER I SENT A FREE TEXT STATING; 'WE NEED L OR R OF COURSE NOW.' THE RESPONSE WAS 'STANDBY.' WE THEN WERE AT A POINT THAT DEV WAS REQUIRED WITHOUT CLRNC. I FREE TEXTED 'DECLARING EMER FOR WX DEV. DEVIATING R OF COURSE.' WE BROADCAST OUR SITUATION ON 123.45. NO OTHER ACFT WERE SEEN VISUALLY OR ON TCAS. WE DEVIATED A MAX OF 7 NM R OF COURSE. AS WE WERE PROCEEDING BACK TO COURSE; WE RECEIVED A RESPONSE; 'DSND TO FL320 AND CLRED TO DEVIATE L10.' I RESPONDED 'UNABLE' AND FREE TEXTED 'PROCEEDING BACK ON COURSE.' NO OTHER COM CONCERNING THIS INCIDENT WAS MADE. THIS IS A FAR TOO COMMON AN OCCURRENCE IN TOKYO (FUKUOKA) OCEANIC. VERY UNRESPONSIVE TO NEEDED WX DEV REQUESTS. 2 OTHER FLTS ON 123.45 AT THE TIME SAID THEY HAD TO DEVIATE WITHOUT CLRNC TO AVOID WX ALSO. I CHOSE TO DECLARE THE EMER. IT APPEARS THAT THE CTLRS HAVE LITTLE UNDERSTANDING OF THE URGENT NEEDS DURING ADVERSE WX OPS.