In Louisiana, the storm system caused flash flooding which took the lives of two people, 13-year-old Sebastian Omar Martinez who drowned in a drainage canal in Bawcomville, LA.
The tornado watch is in effect through 3 a.m. Monday, the NWS said.
Severe weather in parts of the southern United States killed at least eight people and caused damage and power outages.
The next round of severe weather, including tornadoes, damaging winds and hail, is expected to start later this week when a potent storm moves from the Rockies into the Central Plains.
The MSU Crisis Action Team is investigating reports of damage and evaluating the situation.
A microburst "is a localized area of strong straight line winds that descends from a thunderstorm and is less than 2.5 miles in diameter", the weather service said.
"They were at the wrong place at the wrong time", Capt. Alton Lenderman of the Angelina County Sheriff's Office told The New York Times.
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Sheriff Cantrell said there will be more information available Sunday morning.
Meteorologist Monique Sellers said they've received reports of downed trees, as well as damage to buildings and a transmission tower. The death is believed to be storm related, the sheriff's office said.
But "the storm is so vigorous that tornadoes are still possible after dark", he said.
Monroe County Coroner Alan Gurley says multiple people were injured and multiple homes were damaged in Hamilton, Mississippi, which is 140 miles (225 kilometers) southwest of Memphis, Tennessee.
"We were hit really, really, hard. We are just a mess", Cantrell said. Current forecast expectations indicate the possibility of severe thunderstorms to develop that afternoon and track eastward across the state into the evening hours.
The tornado threat will be lower by then, but damaging winds could still present hazardous conditions.