Date: 201509
Location: ZZZ.Airport, US
Flight conditions: IMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: First Officer; Pilot Not Flying
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Weather
Primary problem: Weather

Narrative: Originally filed on the 'A' track; [to] HNL; before takeoff; in consultation with the dispatcher; refiled for the 'B' track to try to stay more south of the weather; and [there was forecasted turbulence in the area]. Approximately 180 NM east of BILLO; FL300; mach .80; VNAV/LNAV engaged with a 1nm [offset] right; [and] the full moon showed a cloud deck ahead of us; appearing to be a dissipating storm; and it appeared we would be just in the tops. I turned the seatbelt sign on; and asked the Flight Attendants (FAs) to be seated. Upon entering the cloud tops; we began encountering continuous moderate turbulence; and momentary periods of severe turbulence; with unintentional 100-200 foot climbs and descents. I asked my First Officer (FO); the Pilot Monitoring; to immediately request a climb to FL320 through SFO Radio; and slowed the aircraft to mach .74 via speed intervene. There was another aircraft on the 'B' track; slightly behind us at FL340; with no [offset] applied. The turbulence continued and increased; and because SFO Radio had failed to contact us with a climb clearance; I asked the FO to contact SFO Radio again to say we were initiating a climb to FL320 without a clearance in an attempt to top the clouds and reach a safer flight situation. The FO did this.I initiated this climb with LVLCHG; and my FO began to announce our climb to other traffic on 123.45.  Upon reaching FL320; the turbulence reduced to just light chop/light turbulence. Within seconds of the leveloff; SFO Radio contacted us to say that FL320 was unavailable due to opposite direction traffic at FL310; 9 minutes ahead; and that we were cleared to maintain a block altitude; FL260-FL300; and to deviate up to 25 NM left or right of track. I immediately initiated a LVLCHG descent to FL280. Upon reaching FL280; we encountered continuous light turbulence. We began to clear the cloud tops at that time; and decided to climb back to FL300; our Sabre FPM altitude. Because we had left the cloud tops behind us; we soon were in just light chop; then smooth flight conditions. I made a PA announcement to the passengers; and then called the FAs on the interphone to talk to them; and to ask if their crew and the passengers were OK. They said all passengers and crew were fine. I allowed the FAs to get up and resume their duties; and approximately 5 minutes later; in smoother flight conditions; turned the seatbelt sign off with a strong recommendation to the passengers to keep their seatbelts securely fastened while seated.I made a logbook entry for the severe turbulence encounter; and made an ACARS report to [maintenance]. The remainder of the flight to block in at HNL were uneventful.


Second narrative: [Report narrative contained no additional information].


Synopsis: A B737 flight crew reported that on an oceanic flight to HNL they deviated from assigned altitude because of moderate turbulence when they had difficulty getting a response from ATC.