Date: 201807
Local time of day: 1201-1800
Location: ZZZ.ARTCC, US
Flight conditions: Marginal
Weather elements / visibility: Thunderstorm; Turbulence
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Communication Breakdown
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Weather; Human Factors; Procedure
Primary problem: Weather

Narrative: We had been cleared direct VOR (ZZZ); and had subsequently been cleared to deviate left of course to get around a large convective area. We were supposed to inform center when we were turning back direct ZZZ. As we continued westward the area off our right hand side appeared highly convective with embedded thunderstorms displayed on the radar; and the area off our left hand side was mostly clear.As we were continuing on our current heading; the center controller started talking to us; but the message was somewhat broken and I didn't catch all of it. What I heard was that we could expect direct ZZZ in about six minutes. We interpreted this to mean that based on what the controller saw on his radar we would be able to go direct ZZZ in six minutes. We could only see the weather to about 40 miles ahead of us; because the corner of a cell was obscuring our view behind it. The onboard weather radar also was not giving us a very clear picture of what was beyond this area. So we assumed that the controller had a better picture of the weather ahead; and we expected to find a break in the weather behind the farthest cell we could see. As we rounded that cell; we saw no break in the weather; and we continued on our heading. Shortly thereafter; the controller told us to proceed direct ZZZ; which would have put us through multiple cells. I requested that we stay on our current heading for a while longer; and the controller again said for us to proceed direct ZZZ and that he told us six minutes ago that we would be direct ZZZ. We replied that we were unable to go direct ZZZ. After a long pause on frequency the captain then transmitted that we could go a few more degrees to the right but were still unable direct ZZZ due to the weather. At this point we were at flight level 380; and were unable to climb higher than the weather. The controller came back on frequency and said 'you either have to turn right direct ZZZ or Identify as an emergency.' So the Captain used his authority for weather deviation; and we continued on our heading. After a few minutes the controller said we were in an active MOA; and that in about six more minutes we would be entering a restricted area. We started our timers; and in 4 minutes we found a hole in the weather and were able to turn direct ZZZ before we entered the restricted area. We both agreed that from that point we could safely navigate around the convective areas and we chose to continue on to destination rather than landing at the nearest suitable airport because our predicament was based on the weather we had already passed. We were handed off to another controller; who then issued us several descent clearances and cleared us for a few more deviations around various cells. We finally cleared all of the weather approximately 50 miles southeast of Destination. We were shortly thereafter cleared for a visual approach into Destination and landed without incident.In my opinion a communication breakdown between us and the controller was the primary reason this situation resulted in us using Captain's authority for weather deviation. I do not know if the controller specifically said that in six minutes we should expect direct ZZZ 'because of an active MOA in front of us.' Neither of us heard that; and were caught off guard when we were told that we had to turn direct ZZZ immediately. Regardless; I should have asked the controller to repeat that transmission or to clarify his meaning so that I could be sure about what was said and expected. Had I done this I would have probably realized that there was an active MOA in front of us and we wouldn't have been surprised at the last minute.In addition to the transmission itself coming in somewhat broken; I think another contributing factor to us not clearly hearing the transmission is that our aircraft did not have a hot inter phone. Because of this; both of us were wearing our headsets with one cup over an ear and the other cup off the earso that we could talk to each other across the center console without having to constantly be pushing the inter phone switch to talk to each other through the headsets. If all the planes had hot interphones; we could more easily wear the headsets normally thereby reducing much of the ambient aircraft noise making it easier to hear ATC transmissions.




Synopsis: B767-300ER First Officer reported they used Captain's authority to deviate around thunderstorms.