Heavy rains were forecast to extend into the Appalachians, affecting parts of Alabama, Tennessee, Kentucky and West Virginia.
The centre of Florence, a Category 2 hurricane, will approach the coasts of North and SC today, the NHC said, adding that it was expected to weaken after it moved inland.
Hurricane Florence is now a category 2 hurricane, with winds of close to 110mph (177km/h).
The outer bands of wind and rain from a weakened but still lethal Hurricane Florence began lashing North Carolina on Thursday as the monster storm moved in for a prolonged and potentially catastrophic drenching along the Southeast coast.
Forecasters predict the storm surge from Hurricane Florence could top 13 feet, enough to send water a half mile inland. There is a chance some of that tropical rainfall could pass through portions of the Northeast next Tuesday or Wednesday before we can finally say good riddance to Florence for good. The storm was moving northwest at 10 miles per hour.
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Early on September 13, NASA's Aqua satellite's infrared data showed the clouds in the southern quadrant of Hurricane Florence appeared warmer than storms throughout the rest of Florence. "We're going to be there to help", Cooper said. "If this blows at 120 mph for four hours, ... you lose a shingle every two minutes, and all of the sudden, you've lost your whole roof after four hours", Myers said. "And that will produce a lot of damage as well as prolong the beach erosion". Closer to central North Carolina, Fayetteville could see winds of 27 miles per hour.
Despite the drop in maximum sustained winds, forecasters stress that this hurricane is not to be taken lightly. Thousands of Marines and their families evacuated from Camp Lejeune, leaving the rest to dig in ahead of what could be a direct hit.
"Today is the time to get your preparedness actions complete", he said.
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The hurricane center also said the threat of tornadoes was increasing as the storm neared shore.
Businesses in Wrightsville Beach, N.C., prepare for Hurricane Florence on Wednesday. Central North Carolina will not feel the worst of the storm until Friday morning.
The surge will result in "large areas of deep inundation. enhanced by battering waves", the Weather Service said.
On Thursday, Hurricane Florence was downgraded from a Category 3 to a Category 2 storm.
Where exactly the zone of heaviest rain sets up as the storm meanders inland is more uncertain, but models suggest that it may concentrate in southern North Carolina and northern SC through the weekend.
Officials in several states have declared states of emergency, including Virginia and Maryland, where coastal areas are still recovering from summer storms.
NHC tropical cyclone forecast track for Hurricane Florence 11 a.m. EDT Thursday. North Carolina alone could get from 20 to 30 inches, with isolated spots possibly receiving 40 inches.
Measurements by an Air Force Hurricane Hunter plane indicate that maximum sustained winds have decreased to near 110 miles per hour, with higher gusts.