SAVANNAH, Ga. — A brutal winter storm smacked the coastal Southeast with a rare blast of snow and ice Wednesday, hitting parts of Florida, Georgia and South Carolina with their heaviest snowfall in nearly three decades. Forecasters warned that the same system could soon strengthen into a “bomb cyclone” as it rolls up the East Coast, bringing hurricane-force winds, coastal flooding and up to a foot of snow. At least 17 deaths were blamed on dangerously cold temperatures that for days have gripped wide swaths of the U.S.