ATL84FA078

The plt received a wx briefing at 1037 EST before departing on an IFR x-country. At 1051, a severe thunderstorm warning (#537) was issued by the national wx svc. When the plt requested an IFR clearance at 1107, he was advised of the frontal activity. About 3 min later, he was briefed on the wx warning, which he acknowledged. At about 1138, the plt was advised of wx in his vicinity & along his planned route which included moderate to severe turbulence & moderate to heavy rain. Based on this info, the plt elected to divert to savannah, GA. At 1139:54, he reported his wx conditions were rough with rain. At 1141:11, the controller noted that his transponder reply showed 2600 ft instead of the assigned alt of 7000 ft. at about that time, radio & radar contact were lost. The acft was presumed to have crashed at sea & both plts were presumed to have been fatally injured. A search of the suspected area was made by the coast guard & debris suspected from the acft was found; however, the main wreckage was not recovered.