The slow-moving storm, the most severe hurricane to threaten the USA mainland this year, was rated a Category 4 on the five-step Saffir-Simpson scale and located about 845 miles (1,360 km) east-southeast of Cape Fear, North Carolina, at 1:30 p.m. EDT (1730 GMT), according to the NHC.
The storm is on track to hit the Carolinas and mid-Atlantic region as early as Thursday, according to the hurricane centre.
The National Hurricane Center said Florence was expected to slam into the coast around North and SC as a Category 3 or 4 hurricane on Thursday or Friday.
Arnold also captured hurricanes Isaac and Helene lining up behind Florence in the Atlantic.
At noon on Monday, Hurricane Florence blew into a Category 4 classification, a level experts previously predicted wouldn't occur until later in the week.
The National Hurricane Center upgraded Florence not once but twice Monday, saying the storm will continue to strengthen as it targets the Carolinas later this week.
Millions in U.S. prepare for potentially catastrophic Florence
Over the weekend , the governors of Virginia , North Carolina and SC declared states of emergency, according to CNN . A mandatory evacuation order was issued noon Monday for North Carolina's Hatteras Island.
"We are preparing for the worst, and of course hoping for the best", added McMaster in his own press release, adding that he made his declaration early to ensure that state agencies could deploy assets quickly. The state's emergency management division has posted additional information on the evacuations and how to prepare.
"Today, let me be clear.North Carolina is taking Hurricane Florence seriously, and you should too". And heavy rains could cause flooding inland for days after landfall.
There are three storms that meteorologists have their eyes on and there's likely more to come.
"With the possibility that Tropical Storm Florence could make landfall in SC, likely as a hurricane, our people have already started making preparations", Attorney General Alan Wilson said. Forecasters say that because of the size the storm is expected to attain, it will wreak havoc regardless of how strong its winds are.
Hurricane Florence is rapidly intensifying and could strike a direct and unsafe blow anywhere from the Carolinas to the Mid-Atlantic region later this week, possibly as a fearsome category 4, forecasters said.
Southeastern North Carolina remains in the middle of the storm's "cone of uncertainty", with the cone extending from roughly Hilton Head, S.C., in the south to the Chesapeake Bay in the north.
And with little wind shear to pull the storm apart, Florence's hurricane wind field was expected to expand over the coming days, increasing its storm surge and inland wind threats, and raising the likelihood of life-threatening freshwater flooding.
An evacuation has already been ordered for Cape Hatteras, but don't wait for hurricane watches and warnings to make a plan, Eck said.
Oosterwyk was gathering tax documents and other important papers from her store on Monday, and said she planned to drive 150 miles (240 km) inland to ride out the storm in the town of Cary. Of the two other storms, which remain far from land, Isaac poses the most immediate risk.
Red flag warnings are keeping swimmers off beaches, as residents sandbag their homes in the communities of Myrtle Beach in SC, and the Outer Banks in North Carolina. It's forecasted to hit the Carolinas on Thursday and Friday.