Date: 202010
Local time of day: 0001-0600
Location: ZMA.ARTCC, FL
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Cruise
Airspace: Class A ZMA
ATC / advisory: Center ZMA
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Captain; Pilot Flying
Anomaly: ATC Issue All Types; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Returned To Clearance; Flight Crew Overcame Equipment Problem
Contributing factors: Human Factors; Weather
Primary problem: Weather

Narrative: In Cruise Flight at FL380 approaching ZZZZZ north boundary of ZZZZ airspace we were denied right deviations for active military airspace. Left deviations at that point were no longer an option and appeared worse. We were on the western edge of a line of weather moving East we were deviating just slightly left of our course to go through what appeared to be the thinnest area of weather on our radar. I had made a PA and had all passengers and Flight Attendants seated. We experienced a brief 10 to 15 seconds of Moderate Turbulence which cause our Altitude to drop 200 ft. to about 37;800 ft. and the a gain of about 300 ft. to about 38;100 ft. and then settled back to level at FL380. We also experienced some airspeed loss and then gain briefly as well as some left bank. It felt much like wake turbulence briefly. Just then MIA center told us to maintain FL380 and contact ZZZZ; before leaving the frequency I stated we had experienced some moderate turbulence which had caused some altitude loss; a couple hundred feet; and that we were now level at FL380 and we were told 'roger' contact Center which we did. The remainder of the flight was uneventful and smooth to destination. [The cause of the event was that] a deviation 100's of miles earlier to the left would have been a better choice and I believe a couple of aircraft behind us after hearing my report to MIA Center deviated into the Military Airspace. I do not know if the aircraft behind me declared an Emergency to do so or not; as we were changing frequency to next center during the radio discussions. That may have been a better choice but I did not expect the turbulence to be that bad; but was very glad I sat the Flight attendants down prior; as well as making a very clear PA to the passengers that we were going to experience some Turbulence since we had to fly in the area of some weather and insisted that they be seated with their seatbelts securely fastened. An earlier plan for weather deviations 100's of mile away if necessary would have helped knowing any right deviations would be denied.


Second narrative: Level at 380 approaching XXXXX; there was some weather close to the intersection. Requested right deviation and Center informed that Warning Areas were active so unable right deviation. We encountered some moderate turbulence in the clouds for a few seconds. The airplane descended 200 ft. before returning to level. Miami informed to maintain 380 and to contact next center over ZZZZ which we did. Flight continued uneventfully.The cause of deviations was not being able to deviate due to Center's instructions.I suggest deviating ahead of time if known that no deviations allowed.


Synopsis: B737-800 flight crew reported moderate turbulence due to weather deviations being unavailable.