No longer a subtropical storm, Alberto remains a threat as it moves inland, drenching the Southeast with more rain after killing at least two people.
Nearly 30 million people are under flash flood watches in parts of Alabama, Tennessee, Georgia and Kentucky for much of Tuesday.
"Alberto weakened to a subtropical depression on Monday night. However, heavy rainfall from Alberto will spread into northern Georgia, the western Carolinas, and Tennessee on Tuesday, increasing the threat of flash flooding in those areas," the National Weather Service said.
After moving into the Tennessee Valley, the system is forecast to head into the Ohio Valley and Great Lakes region Wednesday and Thursday, according to the National Hurricane Center.
About 2 to 6 inches of rain are expected from Alabama to the western Great Lakes and from northern Florida to the mid-Atlantic coast through Wednesday, the hurricane center said.
Florida, Mississippi and Alabama -- the three states bearing the brunt of the storm -- declared emergencies ahead of Alberto.
Swells, which could cause life-threatening surf and rip current conditions, could affect the eastern and northern Gulf Coast through Tuesday, the hurricane center said.
Alberto, the first named storm of the season, is still being felt in Cuba.
A bridge collapsed in Taguasco after heavy rains caused the Zaza River to rise.
This bridge was "vital for land communication between Zaza del Medio and the provincial capital," according to Cuban media reports.
On Monday, two people -- news anchor Mike McCormick and photojournalist Aaron Smeltzer of the Greenville, South Carolina-based CNN affiliate WYFF -- were killed in Polk County, North Carolina. A tree fell on their SUV as they covered the hazardous weather, the station said.
"Two journalists working to keep the public informed about this storm have tragically lost their lives, and we mourn with their families, friends and colleagues," North Carolina Gov. Roy Cooper said in a statement. "North Carolina needs to take Alberto seriously."
Storm makes landfall Memorial Day
Alberto made landfall Monday afternoon as a subtropical storm in the Florida Panhandle, reaching maximum sustained winds of 45 mph as it arrived in Laguna Beach, according to the hurricane center.
It left 6,540 customers in Florida without power, according to the Florida Division of Emergency Management.
Hurricane season is set to begin officially Friday.