There were 10 reported tornadoes from Saturday to Sunday and lightning, hail and heavy rain in Texas and Louisiana.
Francine Gotch, 38, and her daughter, Neville Alexander, 3, were killed when a tornado destroyed their home in St. Martin Parish, Louisiana on Sunday. The National Weather Service confirmed it as an EF-1 tornado with winds of 100 miles per hour.
Fifteen structures were damaged and two were destroyed in Franklin Parish, Louisiana, on Sunday.
In Texas, 74-year-old Clyde Duran drowned on Sunday after being swept into a creek in Mesquite, according to ABC affiliate WFAA. The area had received heavy rain before he fell in.
Nearly 150 damaging storms were reported between Texas and Mississippi over the weekend, with some cities seeing softball-sized hail and winds of up to 70 mph.
Some parts of Louisiana and Mississippi got as much as 10 inches of rain, prompting emergency rescues in flooding neighborhoods.
The storm system, which moved its way through the Gulf Coast on Monday morning, is still producing severe winds in parts of Louisiana, Mississippi, and Alabama.
The NWS put much of the Southeast under a tornado watch until 9 a.m. CDT.
The storm system is expected to move east on Monday and could bring damaging winds, hail and a few tornadoes to Alabama, the Florida panhandle, most of Georgia, and the Carolinas.
Part of the storm system will move into the Midwest and Northeast later on Monday and bring heavy rain and flood threats to those areas.
ABC News' Max Golembo contributed to this report.