On September 19, 1994, about 1839 eastern daylight time, N433US, a Boeing 737-400 experienced turbulence during descent over the Atlantic Ocean. The airplane was owned and operated by U.S. Air,Inc. and was operating as flight No. 811, scheduled, domestic, passenger service from Charlotte, North Carolina, to West Palm Beach, Florida. Instrument meteorological conditions prevailed at the time and an IFR flight plan was filed. The airplane was not damaged and the captain, first officer, 3 flight attendants, and 126 passengers were not injured. One flight attendant received serious injuries. The flight originated from Charlotte, North Carolina, about 1654 the same day. One flight attendant was standing in the rear galley when the airplane experienced one jolt of turbulence. She was evacuated from the airplane upon arrival in West Palm Beach, Florida, and examination revealed she had a fractured lower back vertebrae. The crew stated they were established in descent with the weather avoidance radar on and the airplane encountered one jolt of turbulence. They stated that no echoes were observed on the radar. A factual weather report of the environmental conditions was conducted by the NTSB meteorology division and the airplane was placed in an area of developing convection cells that would not necessarily show up on airborne weather radar. Details of the weather and the report are attached to this report.