"Areas near Newport, North Carolina have seen almost two feet of rain from Florence and powerful rain bands may produce another 15 to 20 inches or more", National Oceanic and Atmospheric Administration (NOAA) representative Steve Goldstein said.
Florence has already set a North Carolina record for rainfall totals, exceeding that of Hurricane Floyd, which struck in 1999 and caused 56 deaths.
"It has already dumped 20 to 30 inches of rain on parts of the Carolinas with more to come", he said. The great danger now, experts say, is river flooding. "If you aren't watching for them, you are risking your life".
As the historic rains and flooding only very slowly ease along the North Carolina coast through Sunday night, serious flooding is predicted to spread farther inland. Cooper asked displaced residents Saturday to resist the urge to return now and wait until the storm clears out and roads are passable.
SC authorities said law enforcement officers were guarding against looting in evacuated areas, while Wilmington set a curfew on Saturday evening in response to looting in one area.
Others killed included three who perished "due to flash flooding and swift water on roadways", according to the Duplin County Sheriff's Office, and a 61-year-old woman who died when her vehicle hit a downed tree.
In Fayetteville, a North Carolina city of about 210,000 people about 90 miles inland, authorities told thousands of residents near the Cape Fear River and Little River to get out of their homes because of the flood risk.
"Remember most storm deaths occur from drowning in fresh water, often in cars".
Mackie rode in a boat through a flooded neighborhood, navigating through trees and past a fence post to get to the Knox house.
Capt. Kelley Hughes of the South Carolina Highway Patrol said the woman, who was wearing a seat belt, died at the scene. "If not we'd be stuck upstairs for the next ... how long?" Its winds were down to 40 miles per hour (75 kph).
Authorities fear the death toll will go higher as the tropical storm crawls westwards across SC.
Ryan Maue, a meteorologist for weathermodels.com, calculated that the storm will dump the equivalent of 18 trillion gallons of rain, enough to cover Texas in four inches of water and fill the Chesapeake Bay.
Major river flooding expected to continue into early next week.
The Neuse is expected to crest at more than nine feet (3 meters) above flood stage Monday and Sheehan said the company expects the same ash basins are likely to be inundated again.
Homes have been washed away by storm surge or made unlivable by standing water, fallen trees or other debris. Farther along the Cape Fear River, grass and trees lining the banks were partly submerged.
North and SC have so far experienced the worst of Florence's slow-crawling path of destruction, where the storm has been responsible for a total of 13 deaths, according to local media. North Myrtle Beach, South Carolina, had about 7 inches.
The floodwaters are expected to push many rivers to all-time highs and, toward the mountains of western North Carolina and southwestern Virginia, could spur life-threatening landslides.
A sailboat is shoved up against a house and a collapsed garage on Saturday after heavy wind and rain from Florence in New Bern.
North Carolina state regulators and environmental groups are monitoring the threat from hog and poultry farms in low-lying, flood-prone areas.