B777-300
Flight Crew Air Transport Pilot (ATP)
Other / Unknown
ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Procedure; Weather
At cruise altitude and flying PIC while captain and other FO on break we received a couple SIGMETs reporting convective thunderstorms with tops at FL540. I plotted the coordinates and saw the lines was anchored on our routing. We requested what looked like best option and 125 miles right of course which was approved. While on this cleared deviation it became apparent we needed more distance to circumnavigate this solid line. I asked to increase another 25-50 miles as needed to work around and through the weather. The request was denied and we were told the best that could be done was 128 miles. So based on my options and my ability to navigate in a clear opening rather than through a massive red return on radar I chose to [use PIC authority] and stay clear as possible and follow emergency weather deviation procedures. We advised ATC and weather deviations after climbing 300 ft we continued and then after clear returned back to clearance and did resequenced of waypoints and reported back on route with ATC. We also SATCOM'd our flights dispatcher and advised of all related information. We returned to course and landed without further events. The event occurred while relief pilots were flying and assigned captain and first officer on break.
[Report narrative contained no additional information.]
B777 flight crew reported the necessity to deviate around weather while in cruise; but only after using PIC authority for the safety of flight.