American Airlines flight 1286 (AAL1286) encountered unexpected convectively induced turbulence (CIT) while at 25,000 ft (FL250) about 17 minutes after departure from Miami International Airport (MIA), Miami, Florida. One flight attendant (FA) received a serious injury, and 3 FAs and 6 passengers received minor injuries. The seatbelt sign was illuminated at the time of the event. No significant convective weather or turbulence was forecasted or depicted during the flight crew’s flight planning or displayed on the onboard weather radar, or WSI weather app before the event. At the time of the event, multiple FAs were conducting cabin service with beverage carts positioned in the aisle, and one passenger was occupying the aft lavatory. The turbulence lasted about 5 to 8 seconds and consisted of abrupt vertical accelerations, resulting in multiple FAs being thrown to the floor or striking interior cabin structures, unsecured service items becoming airborne, and damage to the aft lavatory door. AAL1286 flight crew indicated they had the airborne radar tilt up to 3.5 degrees during the period and likely scanned over the area. Airborne radar does not detect echoes less than 20 dBZ, while echoes of 45 dBZ were detected under the flight track. The model High-Resolution Rapid Refresh (HRRR) sounding indicated a potential for updrafts to 144 knots or 4,173 fpm, and an unstable atmosphere. Following the turbulence encounter, the captain transferred control to the first officer and communicated with the cabin crew to assess injuries. A deadheading captain assisted with cabin coordination and injury assessment. The flight crew contacted dispatch and MedLink and declared an emergency with air traffic control. Based on medical guidance and aircraft position, the decision was made to continue to Raleigh-Durham International Airport (RDU), North Carolina. The airplane landed without further incident. Emergency medical personnel met the flight upon arrival at RDU, and injured crew members and at least one passenger were transported to local hospitals for evaluation and treatment. One FA was diagnosed with a fracture to her arm. A review of the weather conditions indicated that there were no frontal boundaries over the area and no organized jet streams or strong winds aloft to indicate any potential clear air turbulence (CAT). While the NWS convective outlook expected a widely scattered area of general thunderstorms over Florida and the surrounding coastal waters during the time period. The High-level Significant Weather Prognostic Chart indicated no organized areas of convection or turbulence over the general route of flight, and no PIREPs or inflight weather advisories for thunderstorms or turbulence were current at the time of the turbulence encounter. A review of the NWS weather surveillance radar 1988 doppler (WSR88D) and satellite imagery showed an area of scattered echoes over central Florida and off the Florida coast between the Bahamas Islands. A review of the flight path confirmed that the flight over flew an area of developing echoes near 45 dBZ which rapidly increased in height between FL250 to FL420 surrounding the period, while the GOES-19 infrared image indicated radiative cloud tops near FL380 at the time of the turbulence encounter. Several cloud-to-ground lightning strikes were noted with the echoes after the flight had overflown the area of echoes. Thus, other than the flight’s airborne weather radar no visual clues were available prior to the encounter. A HRRR numerical model indicated an unstable atmosphere with potential strong updrafts or maximum vertical velocities (MVV) near to 14,173 fpm. The Eddy Dissipation Rate (EDR) recorded by the accident flight was 0.665 which corresponded to the upper bounds of severe turbulence for a medium weight category aircraft. A review of the astronomical conditions indicated that official nighttime conditions existed at the time of the encounter with no illumination from the Moon, which was more than 30 degrees below the horizon at the time of the encounter.