The National Weather Service confirmed Monday that the tornado that touched down in Shelby and moved across Richland County Sunday was rated EF-2 with maximum wind speeds of 120 to 125 miles per hour.
Both lines of storms are capable of producing damaging wind gusts, isolated hail and even a tornado or two.
Heavy rains and storms raked MS into the night Saturday as the storms moved east.
Clearing is expected to come by the evening with cooler temperatures in the lower 40s.
Two children, siblings aged 3 and 8, were killed on Saturday when a tree fell on the vehicle in which they were sitting in Pollok, Texas, said a spokeswoman for the Angelina County Sheriff's Department. The center said it expects the threat of severe weather to increase throughout the day.
Monroe County will also have a curfew from 8 p.m. Sunday to 6 a.m. Monday.
Authorities say at least 11 tornadoes touched down in three states before the storm began moving towards the East Coast. Thirteen-year-old Sebastian Omar Martinez drowned in a drainage canal in Bawcomville, said Deputy Glenn Springfield of the Ouachita Parish Sheriff's Department, the AP reports.
A MS man, identified as 95-year-old Roy Ratliff died on Saturday when a tornado caused a tree to fall onto his home, Monroe County Coroner Alan Gurley said.
The Richland County Emergency Management Agency reported about a half-dozen homes were damaged and at least six people were taken to a hospital to be treated for storm-related injuries.
Severe weather that moved across the southern USA on Saturday left at least eight people dead, injured dozens of others and ravaged numerous homes in its path.
The roof of a hotel in New Albany, Mississippi, was damaged, although the cause was unclear.
Winds reached 60 miles per hour in Binghamton, the weather service said, as lines of severe thunderstorms rolled into the Northeast Sunday night. The weather service also has a Lake Wind Advisory in place for the city, warning of "strong wind and rough waves on area lakes" that could be hazardous for small craft. A mobile home community was damaged, but no injuries were reported.
The massive storm system sped from Texas eastward with dozens of twisters reported as touching down across the South from Texas through Georgia into Pennsylvania.