"It is still expected to be a large and extremely risky hurricane when it makes landfall", expected late Thursday. "Now's the time to prepare".
Wind gusts topping 100 miles per hour are likely near and just north of where Florence approaches the coast.
By 5 a.m. Tuesday, Florence was centered about 975 miles (1,570 kilometers) east-southeast of Cape Fear, North Carolina, and moving west-northwest at 15 mph (24 kph).
Announcing his evacuation order, SC governor Henry McMaster said an estimated one million people would be fleeing the coast. It's now predicted to make landfall somewhere north of Wilmington, N.C., before its center heads inland toward the cities of Raleigh and Durham.
The governor of neighbouring North Carolina also ordered an evacuation of the Outer Banks, barrier islands that are a popular tourist destination, and parts of coastal Dare County, while a state of emergency was declared in Virginia.
"Zone A is the lowest line and most flood prone area of the Hampton Roads and Eastern Shore", said Northam.
North Carolina governor Roy Cooper said his state was "in the bullseye" of the storm and urged people to "get ready now". "People are doing a pretty good job now". But whenever it makes landfall, the real danger may be rain. The president has spoken to the governors of both Carolinas and Virginia, the White House said Monday.
"Get prepared on the East Coast, this is a no-kidding nightmare coming for you", Gerst said.
Every now and then nature throws out a storm so massive we can only gaze upon it in humbling awe at its fearsome power. It will possibly weaken somewhat as it nears land - but that will hardly change the flooding threat.
"The centre of Florence will move over the southwestern Atlantic Ocean between Bermuda and the Bahamas Tuesday and Wednesday, and approach the southeastern coast of the United States on Thursday", the NHC said.
Even before it officially arrives, Florence will push tall waves far ahead of it.
"Steady weakening is forecast to begin by late Tuesday", the NHC said.
Astronaut Ricky Arnold, who is aboard the ISS, also snapped a picture of the storm, writing that the ISS crew is "thinking of those who will be affected" by its devastation.
Wilmington's National Weather Service Warning Coordination Meteorologist Steven Pfaff has been hard at work updating the local community on what to expect with this storm.
"The big problem is they are now talking about taking hurricane-force winds in as far as the Research Triangle", Watson said, referring to the Raleigh-Durham-Chapel Hill area. If it comes ashore in the region, the hurricane will be the most powerful storm since Hugo slammed into SC in 1989.
Already estimated to bring as much as $27 billion in damages, Florence is aiming for landfall late Thursday or early Friday somewhere between Charleston, South Carolina and Norfolk, Virginia.
If the high remains strong, Florence will take a slower turn to the northwest and be guided onshore over North or SC.
■ "Life-threatening freshwater flooding from a prolonged and exceptionally heavy rainfall event" from the coast to interior sections. Hugo was among the most intense, which made landfall in SC as a Category 4 with 140-mph winds.
Hurricane Helene, heading north in the Atlantic, isn't expected to cause the US any issues, the NHC said.
"That's good news and bad news", he said.
Stewart added, "We're going to have a fairly stable, powerful hurricane with the potential for some additional slow strengthening over about the next 24 hours". Hurricane-force winds could extend more than 50 miles from the storm's center, putting much of the state at risk of destructive winds. Well-built homes can lose walls and roofs. "Electricity and water will be unavailable for several days to weeks after the storm passes". "Most of the area will be uninhabitable for weeks or months". The storm could soon be on the brink of a Category 5.
A warm ocean is the fuel that powers hurricanes, and Florence will be moving over waters where temperatures are peaking near 85 degrees (30 Celsius), hurricane specialist Eric Blake wrote.