South Mississippi is under a tornado watch until 2 a.m. Monday.
The National Weather Service issued the report Sunday evening and said a couple of tornados are possible in southeastern Louisiana, coastal Mississippi and coastal waters.
A tornado watch means conditions are favorable for tornadoes and severe thunderstorms. The weather service said a gradual increase in tornado threat is apparent across the area through at least part of the overnight.
The area included in the watch is from 40 miles south of New Orleans to 50 miles east of Gulfport, which includes the three Coast counties and the waters to the south.
The coastal flood warning and flash flood watch also are in effect until Monday, with 3 to 7 inches of rain predicted for South Mississippi and more possible in some areas.
Heavy rain that soaked Texas moved into South Mississippi on Sunday, turning what was a burn ban for the entire state into flood watches and warnings for the Coast counties through 1 p.m. Monday.
NWS says heavy rain and breezy conditions will continue on Monday, with the chance of showers diminishing to 40 percent Tuesday. The forecast for Wednesday is mostly sunny skies.
A low pressure system that brought flooding in Texas and leftover moisture from Hurricane Patricia are bringing the heavy downpours to the Coast.
"With us being under a burn ban any rain is much needed," said Rupert Lacy, emergency management director for Harrison County. The long-range forecast is for more rain next weekend.
Brian Adam, director of emergency management for Hancock County, was out checking roads for possible flooding as it's rained on and off early Sunday afternoon.
Water levels are low in area rivers and streams and Lacey said that if the rain isn't too heavy at the start, the ground that is hard from the recent drought conditions will start to absorb the water.
"If we get slammed with heavy-duty hard rains it's just going to run off and go to the streams," he said.
People in South Mississippi should be cautious to the amount of rainfall, he said, especially if the area gets 7 inches in a day or a day and a half.
A small craft advisory is in effect for South Mississippi, with gusts to gale force possible, and is expected to continue through Tuesday.
Tides could rise 2 feet above normal, according to the weather service, causing minor coastal flooding, especially around the time of high tides.