On Tuesday, downpours and gusty thunderstorms will drench areas from central Texas to central Arkansas and southern Tennessee, AccuWeather said.
The new weather system will further soak sodden areas through Thursday, weather.com meteorologist Chris Dolce said.
"After a few dry days, rain will return to some of the waterlogged cities in those regions, exacerbating the flooding situation," Dolce said.
Roughly 70 rivers were in flood stage as of midday Monday in the central USA, the National Weather Service said. Overall, more than 250 river gauges reported levels above flood stage from the Great Lakes to Texas. (Each river can have several gauges.)
The greatest concern in coming days will be in Arkansas, Tennessee, Kentucky, Mississippi, Alabama and Georgia on Wednesday into early Thursday.