It's the sheer volume of water, in the form of tidal surges, rain, and anticipated flash flooding that make this Category 1 storm unusually unsafe.
North Carolina Governor Roy Cooper advised residents and visitors to remain inside, warning that the risk of fatalities will increase once the winds die down.
Craven County emergency crews put out the message to people stranded to shelter in place, as 150 people were waiting for help before midnight Thursday.
A mother and her young child were killed when a tree fell on their house in Wilmington, North Carolina.
The father was injured in the incident and was transported to a hospital, officials said.
Video from Belhaven, North Carolina, showed storm-surge flooding up to the window-level of a house early Friday morning. Also, a 77-year-old man was apparently knocked down by the wind and died after going out to check on his hunting dogs, Lenoir County authorities said, and the governor's office said a man was electrocuted while trying to connect extension cords in the rain.
Hundreds of people needed to be rescued after becoming trapped in their homes by a storm surge of up to 10 feet (three meters) in New Bern, a town of 30,000 in North Carolina at the confluence of the Trent and Neuse rivers. "America is proud of you", Trump tweeted on Friday, referring to the Federal Emergency Management Agency, which responds to disasters in the United States.
Resident Jay Manning said he and his wife watched with alarm as water filled the street. "My wife's in a panic right now".
"The imminent threat of coastal flooding and high winds have passed for our coastal communities as Hurricane Florence has made landfall in the Carolinas and we believe it is safe for Virginians to begin returning home", Northam said in a statement.
"It's the first time we've ever had to move anything like this", Rose said. "This is a 500- or 1,000-year event".
The 400 mile-wide storm's winds weakened to 70mph after it reached the coast, well below the 140mph seen earlier this week.
North Carolina alone is forecast to get 9.6 trillion gallons, enough to cover the Tar Heel state to a depth of about 10 inches.
Tropical Storm Florence's relentless rain has caused devastating flooding in the Carolinas and promises even more Saturday, a day after it landed as a hurricane and left at least seven people dead - including a baby. Neighborhoods are flooded after the storm surge from Tropical Storm Florence flooded the Neuse River on September 14, 2018 in New Bern, North Carolina.
About 1.7 million people in North Carolina, South Carolina and Virginia are under voluntary or mandatory evacuation orders, and millions of others live in areas likely to be affected by the storm. "In addition to the ongoing, risky storm surge and flash flooding, will be a long-term river flood threat WELL INLAND as very heavy rainfall continues to fall in the coming days".
Morehead City, North Carolina, had received 23 inches of rain by Friday night, and forecasters warned Saturday morning that parts of the Carolinas could get up to 15 inches more.
Utility companies said millions were expected to lose power and that restoring it could take weeks.