The NHC said the first tropical storm-force winds of at least 63km/h would hit the region early on Thursday with the storm's centre reaching the coast Friday. "T$3 his is a no-kidding nightmare coming for you".
Duke Energy, the nation's No. 2 power company, said Florence could knock out electricity to three-quarters of its 4 million customers in the Carolinas, and outages could last for weeks.
By Sunday, clouds from Florence will increase around here, with rain arriving by Sunday night into Monday.
At 11am local time on Wednesday (early Thursday AEST), the storm was located about 785km southeast of Wilmington, North Carolina.
The path of Hurricane Florence could affect the homes of more than 5 million people, and more than 1 million of them have been ordered to evacuate.
A state of emergency has been declared in Maryland, North Carolina, South Carolina, Virginia and Washington amid concern over potential torrential rain and flooding. Georgia Gov. Nathan Deal followed suit on Wednesday. Rather than pushing up toward western Virginia, the storm's center is now predicted to move across eastern SC on Friday night and Saturday.
Tropical disturbance Invest 95L as of Wednesday morning.
A storm covering enormous area, to drench and lash more people.
And the storm surge, which could be as much as 12 feet in some areas, will be on top of sea level rise from climate change.
"This morning I drove around for an hour looking for gas in Cary".
The New York Army National Guard is ready to deploy four helicopters - two CH-47 Chinooks and two UH-60 Blackhawks - to help storm response efforts. In North Carolina, Cooper says, "2,800 soldiers will be on active duty, joined by even more on standby".
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Previously, Arnold shared images of Florence initially gaining strength over the ocean.
People in areas vulnerable to a risky hurricane have left or are fleeing ahead of the storm's expected Friday or Saturday landfall.
Satellites orbiting Earth have also been keeping tabs on Florence from above.
The NHC said Helene was weakening, however, and posed no danger to land.
Florence is one of the strongest hurricanes to hit the eastern coast in decades.
Predictions now have the storm stalling and making a slight southward turn after it makes landfall.
Senior National Hurricane Center specialist Stacy Stewart said the impacts of the storm will cover a wide area "regardless of exactly where the center of Florence moves".
The lingering storm could bring days of heavy rains, which could spark intense floods from SC to Virginia. North Carolina alone could get from 20 to 30 inches, with isolated spots possibly receiving 40 inches.
"An Air Force Reserve Hurricane Hunter aircraft that was in the hurricane until just after midnight" recorded a peak wind gust of around 150 miles per hour, according to the hurricane center.
"While it remains possible the system becomes a tropical storm, we see no reason right now to believe it becomes more than that, and we're not convinced it develops at all", said Space City Weather's Eric Berger in the blog. "It goes well inland".
Jeff Byard of the Federal Emergency Management Agency invoked a former boxing champion to warn residents that it would bring "a Mike Tyson punch to the Carolina coast".
"But despite that, bad things can happen when you are talking about a storm this size", he added. "It's called Mother Nature".