(Reuters) - Residents of Southern states along the Mississippi River are bracing for the flooding that has swamped communities in Illinois and Missouri over the last week, causing thousands of evacuations and killing at least 29 people.

Submerged roads and houses are seen after several days of heavy rain led to flooding, in an aerial view over Union, Missouri, December 29, 2015. REUTERS/Kate Munsch

Officials in Louisiana are checking levees daily, and Exxon Mobil Corp has decided to shut its 340,571 barrel-per-day refined products terminal in Memphis, Tennessee, as floodwaters threatened to inundate the facility just south of the city’s downtown.

“All that water’s coming south and we have to be ready for it,” Louisiana Lieutenant Governor-Elect Billy Nungesser told CNN. “It’s a serious concern. It’s early in the season. We usually don’t see this until much later.”

Workers in Tennessee were preparing for the Mississippi River in Memphis to reach flood stage over the weekend.

“We’re moving things up high and we’ve got our generators out and got some extra water,” said Dotty Kirkendoll, a clerk at Riverside Park Marina on McKellar Lake, which feeds off the Mississippi River.

Flooding in the U.S. Midwest typically occurs in the spring as snowmelt swells rivers. Freezing weather in the region has added to the challenges as the waters have slowly started to recede from the St. Louis area.

Most of the deaths from the rare winter floods have been caused by people driving into flooded areas after days of downpours. Two teenagers remain missing in southern Illinois after their truck was recovered late on Thursday night.

Twelve Illinois counties have been declared disaster areas, and Gov. Bruce Rauner on Friday ordered Illinois National Guard troops into flooded areas in the southern part of the state to mitigate flood damage and help with evacuation efforts.

The Mississippi River is expected to crest at Thebes, in southern Illinois, at 47.5 feet (14 meters) on Sunday, more than 1-1/2 feet above the 1995 record, the National Weather Service (NWS) forecast.

Flood warnings were also in effect on Friday for parts of Texas, Oklahoma, the Carolinas, Alabama and Kentucky, the NWS said, while major flooding was occurring on the Arkansas River and its tributaries in that state.

Dozens have died in U.S. storms, which also brought unusual winter tornadoes and were part of a wild worldwide weather system over the Christmas holiday period that also saw severe flooding in Britain.

More than 100,000 people were forced to evacuate their homes in areas bordering Paraguay, Uruguay, Brazil and Argentina after floods due to heavy summer rains caused by El Niño, authorities have said.

Global weather dominated conversation on social media over the holiday season after the international climate deal in Paris.

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Particularly hard hit in the United States in recent days has been Missouri, which has suffered historic flooding.

Close to St. Louis on Friday, the Mississippi River, the second-longest river in the United States, was falling after reaching near-record heights, the NWS said.

The Meramec River, which meanders near St. Louis and empties into the Mississippi River, broke height records on Thursday, sending a deluge of water over its banks and forcing the closure of two major highways.

Interstates 55 and 44 reopened on Friday, but many other roads remained closed in the St. Louis area, state officials said, causing extreme traffic congestion.

Thousands of people evacuated from their homes earlier in the week were waiting to return to their communities and begin the process of cleaning up. Hundreds of structures have been damaged or destroyed, local officials said.