Southeastern coastal North Carolina and far northeastern SC are expected to get pelted with 20 to 30 inches of rain, and some isolated spots may get up to 40 inches in 48 hours.
A later tally estimated about 350 people in New Bern needed to be rescued from flooding on the Neuse River, and about 70 people in Jacksonville, North Carolina, had to be moved to safety from a hotel whose structural integrity was threatened by the hurricane.
Authorities in New Bern said more than 100 people had to be saved from floods and that the downtown area was underwater.
New Bern resident Latasha Jones is one of the more fortunate ones.
"You can see there's fish floating around in here. We have also gotten calls from family members anxious about relatives they can't reach".
Definitely the storm surge, which could be up to 11 feet in some locations. We have steps on the sides of the house so it's a few feet off the ground anyway.
"On a scale of 1 to 10, I'm probably a 7" in terms of worry, she said.
About 10 million people could be affected by the storm and more than one million were ordered to evacuate the coasts of the Carolinas and Virginia. People tend to check social media more frequently during breaking news events, and it becomes even easier for manipulated weather projections and deceptive survival tips to go viral.
"The National Hurricane Center said Florence is moving very slowly to the west at only 6 miles an hour, then is expected to turn to the southwest, increasing the threat for historic storm surge and catastrophic flooding to coastline areas and inland cities in North Carolina and SC".
The center said the threat of freshwater flooding will increase over the next several days.
The storm's movement, not its strength, has forecasters and officials anxious.
More ominously, forecasters said the onslaught would last for hours and hours because Florence was barely creeping along at 6 mph and still drawing energy from the ocean. As of 2 p.m., the storm was about 35 miles west-southwest of Wilmington, N.C., and about 35 miles east-northeast of Myrtle Beach, S.C.
Florence's winds weakened as it drew closer to land, dropping from a peak of 140 miles per hour (225 kph) earlier in the week, and the hurricane was downgraded from a terrifying Category 4 to a 1.
Tornadoes are also possible.
The Pentagon has dispatched two ships and a Marine unit offshore to provide help if needed.
Eight entire counties and portions of others in North Carolina are under mandatory evacuation orders. "If you're called to go, you need to go".
Vicki Moulson, who teaches at a local community college in the Outer Banks, said she was planning to ride out the hurricane because she wants to be near her home and her friends.
The police chief of Wrightsville Beach suggested that those who made a decision to stay give him their next-of-kin contact information.
"This is an absolute life-threatening scenario".
"Incredible job being done by FEMA, First Responders, Law Enforcement and all".
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Joyce, with winds extending about 35 miles from its center, is expected to tap the brakes a bit and turn eastward by Friday night, and then accelerate northeastward over the weekend.