Weather?
Associated Press drops a heavy hint that the a/c might have been caught by Tropical Storm Tomas. Possibly something to it: the METARs at the nearest reporting station (MUSC, admittedly about 50 nm to the NW) show some convective activity around the time of the accident, though nothing very unusual. But the flight was heading in the opposite direction to the storm. Again, more information required on this one.
MUSC 042353Z 25004KT 9000 BKN020CB 23/22 Q1007
MUSC 042252Z 28006KT 8000 BKN020CB 24/22 Q1006
MUSC 042152Z 23006KT 8000 BKN020CB 26/22 Q1005
MUSC 042055Z 26004KT 9000 FEW020 BKN100 26/23 Q1005