Florence crashed into the Carolinas on Friday with 90-mph (144 kph) winds, torrential rains and a powerful storm surge before slowing to a pace that meant it would plague the area with days of flooding.
"We can show you what this could look like, if you were to find yourself in this scenario", meteorologist Erika Navarro says. "To those in the storm's path, if you can hear me, please stay sheltered in place".
Florence dumped more than 20 inches on Oriental, N.C., the NHC said.
More than 80,000 people were already without power as the storm approached, and more than 12,000 were in shelters.
After maintaining Category 4 or 3 status most of Wednesday, Florence was a Category 2 storm with maximum sustained winds of 110 mph churning about 205 miles southeast of Wilmington, according to a 5 a.m. briefing by the National Hurricane Center.
Cooper said Florence was set to cover nearly all of the state in several feet of water.
North Carolina's Emergency Management tweeted that more than 154,000 homes were already without electricity by late Thursday.
National Weather Service forecaster Brandon Locklear predicted Florence would drop up to eight months' worth of rain in two or three days.
In Craven County, authorities say they have received more than 150 telephone calls from people in the historic town of New Bern asking to be rescued because water has entered their homes.
More than 60 people had to be pulled from a collapsing motel at the height of the storm, and many more who defied evacuation orders were hoping to be rescued. The county has five swift water rescue teams out to answer calls for help, alongside citizen volunteers with the Louisiana Cajun Navy. "We've had it reported to where it's over mailboxes, to the stairs of homes, even at first, second floors to where people are having to get on their roofs".
Around midday, Spanish moss blew sideways in the trees as the winds increased in Wilmington, and floating docks bounced atop swells at Morehead City. "I have no generator", said Petra Langston, a nurse.
"It's insane", he said in a phone interview.
'I see a biblical proportion flood event that's going to occur, ' Wilmington Police Chief Ralph Evangelous told ABC News. And while the intensity of Florence's winds - still in the 90 miles per hour range - have diminished enough to turn it into a Category 1, the storm has grown in size as it crawls off the coast at a plodding 6 miles per hour.
North Carolina is now facing the brunt of the storm, though that's likely to change since weather forecasts predict Florence will head inland before moving north, towards Virginia and Maryland. Significant weakening is expected over the weekend.
Florence will crawl along the coast through Friday bringing a relentless period of winds gusting over 100mph along with heavy rainfall.
One climate model is predicting that as much as 11 trillion gallons of rain will fall on North Carolina in the coming week - an amount that's enough to fill the Empire State Building 40 times over.