Florence’s slow-motion grind across the Carolinas is coming to a welcome end after dropping staggering amounts of rain that swamped communities and left swollen rivers ready to overrun their banks.

The storm was expected to leave South Carolina behind overnight after weakening to a tropical depression Sunday. But it got in some parting shots as it whirled to an exit, lashing North Carolina and northern portions of the Palmetto State with thick sheets of rain and blustery thunderstorms.

That only added to the rainfall — measured in feet in some parts of North Carolina — that’s expected to gush downstream in the coming days and cause extensive, catastrophic river flooding.

The death toll from Florence rose to 17 as hundreds of people were evacuated from their homes and Wilmington, N.C., a city of 120,000 people, became a virtual island, cut off from the rest of the state by floodwaters.

A portion of Interstate 95 through Dillon County was shut down as well, and evacuees returning to other parts of South Carolina found a mix of snarled traffic and water-logged roadways in some areas. The storm flooded cotton fields in Bennettsville, overran rural highways in Cheraw and herded some 4,000 people to a network of shelters throughout the state.

South Carolina Gov. Henry McMaster said no one knows how high the rivers will rise or when flash floods might occur. He urged people in low-lying areas to avoid roads where standing water might make a washout.

"Please heed the warnings that are given to you," he said. "We do not want to lose lives to this water. These are avoidable tragedies."

A deadly deluge 

All told, the storm was expected to dump 18 trillion gallons on the Carolinas, enough to cover the entire state of Texas with 4 inches of water, a forecaster said. It has claimed six lives in South Carolina, including a 23-year-old man killed Sunday in Georgetown County after the truck he was riding in hydroplaned and flipped on a flooded road. The same day, the driver of a pickup truck in Kershaw County died after crashing into an overpass support beam on Interstate 20. Another pickup truck driver died near Gilbert after plowing into standing water on the roadway, according to the state Highway Patrol.

As of Sunday, some 61,000 power outages in South Carolina had been reported. The storm also triggered hundreds of rescues in North Carolina and knocked out power to nearly a million people.

Some sections of South Carolina didn't see a drop of rain; others were inundated. Goose Creek, for instance, saw less than an inch of rain while Jamestown, 37 miles away, had more than triple that amount, according to the National Weather Service. Chesterfield County, along the North Carolina border in the Pee Dee region, recorded the highest rainfall total in the state, with just over 16 inches. Marion County, about 80 miles to the east, was next up, with 15.4 inches.

While bright sunshine returned to the Charleston area, Florence continued to drill the upper half of the state, particularly along the North Carolina border. There, police, firefighters and city workers battled to clear backed up storm drains and pooling water as they braced for rising rivers in the days to come.

The effects of Florence will be felt well into the coming week, with some rivers not expected to crest from flooding until Friday. The National Weather Service warned of the potential for "life-threatening, catastrophic flash floods and prolonged significant river flooding."

Communities up and down the Pee Dee, Lumber and Waccamaw rivers braced for an onslaught of water rushing downstream from North Carolina, where several feet of rain have fallen since Florence made landfall Friday packing 90-mph winds.

Coal ash threats

As of Sunday evening, the epicenter of the crisis will likely be Conway, where the Waccamaw River is expected to hit 17 feet by Friday — just inches shy of the record set in 2016 by Hurricane Matthew.

That prediction was less dire than earlier forecasts indicated, but such a marked rise would still pose a threat to dikes around a coal ash dump next to a closed Santee Cooper power plant. A failure in the earthen berms could unleash 200,000 tons of ash laced with toxic chemicals into the Waccamaw, which drains an area the size of Rhode Island as it snakes roughly parallel to the coast near Myrtle Beach.

Santee Cooper has mounted an all-out effort to keep the dikes from failing. Workers have mobilized excavators and bulldozers in case of a breach. They've also filled giant bags of rocks that can be dropped by a helicopter to plug any gaps that form. Utility workers also pumped water into the ponds to equalize pressure on the berms as the river rises next to them.

Santee Cooper had about 30 workers on site Sunday, and a helicopter capable of lifting the heavy bags was expected to be in place by the afternoon, said utility spokeswoman Mollie Gore.

“We have a plan and we are working through that plan,” she said.

McMaster on Sunday asked Santee Cooper to act immediately, stating in a letter to the utility that he was “seriously concerned” about the structural integrity of the ponds and the environmental risks associated with anticipated flooding.

Duke Energy, meanwhile, said the collapse of a coal ash landfill at a closed power station near the North Carolina coast was an "ongoing situation," with an unknown amount of potentially contaminated storm water flowing into a nearby lake. Duke spokeswoman Paige Sheehan told the Associated Press Sunday that a full assessment of how much ash escaped at the Sutton Power Station outside Wilmington can't occur until it stops raining.

Duke was also monitoring coal ash basins at its Robinson Plant in Darlington County and its retired Weatherspoon Plant near Lumberton, N.C., but there were no indications flooding posed an immediate threat to either location, said Megan Henderson, a Duke spokeswoman. About 3.2 million tons of coal ash are located at Robinson; another 2.2 million tons at Weatherspoon, not far from the Lumber River, she said.

Making do

Despite the threats, some were taking the storm in stride.

“We’re in good shape,” Cheraw resident Dwight Parke said as he inspected the flooded roadway in front of his house. “This is just a minor inconvenience.”

Parker's rain gauge showed the tiny town on the Pee Dee River had received just over a foot of rain over Saturday and into Sunday. He said it’s likely the worst flooding the town had seen since 2015.

During that storm, he had several feet of water enter his basement. This time around, he bought a better pump, he said.

In Conway, the clouds had parted by early afternoon and the sheets of rain had died away.

Don Frazier took the opportunity to go for a run on the city's Riverwalk Trail before officers closed it off to make way for the rising Waccamaw.

Frazier and his wife fled their home in Myrtle Beach last week to escape the predicted ocean surge on the coast. Now they were busy packing up their condo in Conway to escape the swollen river.

“You can’t beat Mother Nature,” Frazier said.

Reach Glenn Smith at 843-937-5556. Follow him on Twitter @glennsmith5.