On August 5, 2017, at 1435 eastern daylight time, an Airbus 330, N276AY, operated by American Airlines as flight 759 encountered turbulence at 28,000 feet about 25 miles east of East Hampton, NY. One flight attendant suffered a broken arm and there were 10 minor injuries among the passengers and flight attendants. The airplane was not damaged. The flight was a regularly scheduled passenger flight from Athens, Greece, to Philadelphia, Pennsylvania (PHL). According to the operator, the flight passed very close to a small, but rapidly developing convective cell with tops near FL300. A steady increase in lightning reports was noted immediately after encountering the cell. The cell was most likely dominated by updrafts at the time of the encounter and dissipated 30 minutes after the report. Other isolated to scattered areas of convection were developing along a cold front over Eastern Long Island at the time. ATC radar depicted an area of moderate to extreme precipitation returns along the airplane's route of flight. ATC did not advise the flight crew of the returns until after the crew reported the turbulence encounter. The flight crew reported that the seat belt sign was on at the time of the turbulence.