With rivers swelling toward record levels, thousands of people were ordered to evacuate for fear the next few days could bring the most destructive round of flooding in North Carolina history.
Florence's intensity has diminished since it roared ashore along the US mid-Atlantic coast on Friday as a hurricane.
Florence is 350 miles (560 km) wide and has travelled 4,000 miles across the ocean from west Africa.
The storm was expected to move across parts of southeastern North Carolina and eastern SC on Friday and Saturday (September 15), then head north over the western Carolinas and central Appalachian Mountains early next week, the NHC said. Gusts reached over 100 miles per hour - the highest recorded in North Carolina since 1958.
Rivers and creeks rose toward historic levels, threatening flash flooding that could devastate communities and endanger dams, roads and bridges.
"This is a hurricane event followed by a flood event", said South Carolina Governor Henry McMaster.
The death toll from the hurricane-turned-tropical storm had climbed to 13 by Saturday evening with 10 deaths reported in NC and three in SC.
"These rainfall amounts will produce catastrophic flash flooding, prolonged significant river flooding and an elevated risk for landslides in western North Carolina and far southwest Virginia", the hurricane center warned.
Utility crews worked to restore electricity.
Photos and videos from around the region, and particularly North Carolina, showed the power that Florence contained as it came ashore, leading to rescues across the area.
Razer Phone 2 gets ready to make an October 10 debut
Razer Phone 2 will be a successor the original Razer Phone , one of the first smartphone in the market with a 120Hz display. Interestingly, the event invite mentions "flagship gaming" and shows a green outline of what appears to be a smartphone.
Hong Kong raises typhoon alert as Mangkhut approaches
More than 500 flights have been canceled affecting some 96,000 passengers, according to the South China Morning Post . Many residents have begun preparing for the storm by reinforcing their homes and buying food and supplies in bulk.
Trump on Hurricane Maria
Almost 3,000 deaths have been attributed to Hurricane Maria , making it the second-deadliest storm in the US. There are also no state or federal guidelines in the U.S. for calculating storm or hurricane-related deaths.
Florence peaked at a terrifying Category 4 with top winds of 140 mph over warm ocean water before making landfall as a Category 1 hurricane at 7:15am at Wrightsville Beach, a few miles east of Wilmington and not far from the SC line.
Heavy rain and flooding are expected to continue at least through the weekend, and local officials said hundreds in areas hit by Florence still need rescue.
The storm has killed at least 11 people in North and SC, authorities said.
On Friday, North Carolina Gov. Roy Cooper called Florence an "uninvited brute who doesn't want to leave", warning it could wipe out entire communities as it grinds its way across land.
The storm made landfall on Friday near Wilmington, a city of about 120,000 squeezed between North Carolina's Atlantic coastline and the Cape Fear River.
Duke spokeswoman Paige Sheehan said about 2,000 cubic yards (1,530 cubic meters) of ash were displaced at the L. V. Sutton Power Station outside Wilmington and that contaminated runoff likely flowed into the plant's cooling pond.
Florence already has set a North Carolina record for rainfall totals, exceeding that of Hurricane Floyd, which struck in 1999 and caused 56 deaths.
As of noon, Emerald Isle had more than 23 inches (58 centimeters) of rain, and Wilmington and Goldsboro had about a foot (30 centimeters). Some area residents described a harrowing retreat as the storm hit.
In a subsequent tweet, Mr. Trump claimed that the reporting was "done by the Democrats in order to make me look as bad as possible when I was successfully raising Billions of Dollars to help rebuild Puerto Rico".
The Weather Channel's Mike Seidel was seemingly battling to stay upright as he filmed a piece in North Carolina - only for two pedestrians to calmly stroll past in the background.