Millions urged to flee inland hours before it was due to announce its arrival with torrential downpours..
About 10 million people could be affected by the storm and more than 1 million had been ordered to evacuate the coasts of the Carolinas and Virginia, jamming westbound roads and highways for miles.
Masters said there's a tug-of-war between two clear skies high pressure systems - one off the coast and one over MI - and the more the Great Lakes one wins, the more southerly Florence will be.
Georgia joined four other coastal states issuing an emergency declaration as the latest forecasts showed Florence dumping historic amounts of torrential rain on the southern state.
'This storm is a monster.
"Get prepared on the East Coast, this is a no-kidding nightmare coming for you", Gerst said.
If the European model is true or the overall trend persists, University of Miami hurricane researcher Brian McNoldy said it "is exceptionally bad news, as it smears a landfall out over hundreds of miles of coastline, most notably the storm surge. he rainfall has been and continues to be a very substantial threat over the entire area".
Landfall is expected late Thursday or early Friday, and the National Hurricane Center fears the storm "will slow considerably or stall, leading to a prolonged and exceptionally heavy and risky rainfall event Friday-Sunday". "Don't play games with it". "We'll handle it. We're ready, we're able".
The president said: "The safety of American people is my absolute highest priority".
Florence is forecast to dump up to 40 inches (one meter) of rain in some areas after it makes landfall in North and SC.
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Avair Vereen, 39, took her seven children to a shelter in Conway High School near Myrtle Beach, South Carolina . Millions of people are expected to lose power and it could take weeks to resolve the outages.
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But that toll should have at least another 1,000 added to it because that's the number of people who died due to debris exposure. Those involved with the study have emphasized that the 3,00 estimate is not a conclusive number and further work should be done.
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The National Weather Service also predicts "catastrophic flash flooding and prolonged significant river flooding" in parts of the Carolinas and Appalachians.
"This is going to be a Mike Tyson punch to the Carolina coast", said Jeff Byard, associate administrator for response and recovery at the Federal Emergency Management Agency.
The country's No. 2 power company said Wednesday that it's anticipating 1 million to 3 million homes and businesses could lose power for lengthy periods, depending on the storm's track.
Early Wednesday afternoon in North Carolina, the storm was centered 700 kilometers (435 miles) off the coast, moving at 26 kph (16 mph) towards the U.S. coastline.
Officials in several states have declared states of emergency, including in the Carolinas, Georgia, Virginia and Maryland, where coastal areas are still recovering from summer storms. "There's nobody left to work".
And there's "a huge difference" in the size and type of damage Florence inflicts if it stays 50 miles (80 kilometers) off shore versus heading inland immediately, Landsea said. "The building's solid and Buddha will protect us".
"What can you do?" she asked. "Because it's Mother Nature".
In a trailer park outside Wilmington, Alondra Espinoza was preparing to leave with her two young children. The two hardware chains said they sent in a total of around 1,100 trucks. "If I can't get back in a week, after a while they might turn on each other or trash the place".
"We do not want to risk one SC life in this hurricane", the governor told reporters.
On another barrier island just below the Bogue Banks, Steve Harrigan reported live from North Topsail Beach, where visitors and residents were largely heeding warnings from Gov. Roy Cooper (D-N.C.) to evacuate.