More unwelcome rain is forecast this week in much of the central and southern USA, falling upon areas already swamped by record-breaking floods.

"Many locations from the central and southern Plains into the Mississippi Valley and Ohio Valley could see 1 to 3 inches of rain in the week ahead," the Weather Channel warned, with "locally up to 5 inches of rain possible in some areas."

To make matters worse, rain from a developing tropical storm in the Gulf of Mexico could bring additional rainfall to the region: "Tropical moisture from the western Gulf of Mexico may begin impacting parts of south Texas on Tuesday," the National Weather Service said.

The weather system, which will be named Tropical Storm Barry if its winds reach 39 mph, is sitting in the Gulf just east of Mexico.

According to the National Hurricane Center, the "system is expected to move slowly northwestward toward the northeastern coast of Mexico and could become a tropical cyclone before it moves inland in a day or two."

Regardless of whether it becomes a tropical storm, moisture from the system "will spread north and eastward," the weather service said, "with heavy to excessive rainfall a concern especially across regions with current and ongoing moderate to major flooding."

Heavy rainfall from the system is likely to spread over southeastern Texas and Louisiana through Thursday, the hurricane center warned.

The worst of the river flooding is in Arkansas and Missouri, the National Weather Service said.

Along the Arkansas River in Arkansas, communities prepared for more record-breaking crests. Officials ordered mandatory evacuations for about 500 homes that sit within the levee system in Jefferson County, just southwest of Little Rock.

"Just horrible scenes down in Jefferson County and Pine Bluff, Arkansas," tweeted Brian Emfinger of KATV-TV in Little Rock on Sunday.

In North Little Rock, which sits across the river from the capital city, officials went door-to-door Saturday to urge residents in about 150 homes near the river to consider leaving.

“We’ve lived here for 12 years. Never been like this,” said Larry Campbell as he packed up his belongings of his North Little Rock home into the back of a truck, according to KTHT-TV in Little Rock. “It’s tough. It’s really tough.”

“You have to just make a decision because you’re going to lose everything,” Campbell said as he choked back tears.

In Missouri, the swollen Missouri and Mississippi Rivers forced hundreds of roads to close and inundated homes and businesses.

In St. Louis, several hotels crowded with visitors for the Stanley Cup Final and Cardinals-Cubs baseball games were left without hot water Sunday after too much water overwhelmed a pump station.

Heavy rainfall over the past few weeks shattered records for May throughout the central USA, swelling rivers to record levels in parts of Arkansas, Kansas, Missouri and Oklahoma.

Ten locations have set record river levels during this prolonged siege of heavy rain, the Weather Channel said.

Contributing: The Associated Press