The South Carolina governor has ordered the state's entire coastline to be evacuated as Hurricane Florence rapidly strengthens into a potentially catastrophic Category 4 storm.
Florence is closing in on North and South Carolina, carrying winds and water that could wreak havoc over a wide stretch of the eastern United States later this week.
The first effects of what forecasters are already calling a large and extremely dangerous hurricane were already being seen on barrier islands yesterday as dangerous rip currents and seawater flowed over the state highway.
People were told to prepare to evacuate communities up and down a stretch of coastline already identified as particularly vulnerable to rising sea levels due to climate change.
For many, the challenge could be finding a safe refuge: If Florence slows to a crawl just off the coast, it could carry torrential rains up into the Appalachian mountains, causing flash floods, mudslides and other dangerous weather across a wide area.
National Hurricane Center Director Ken Graham warned that Florence was forecast to slow down significantly and linger over the Carolinas once it reaches shore, dropping heavy rainfall as far as West Virginia. People living well inland should prepare to lose power and anticipate flooding and other hazards, he warned.
"It's not just the coast," Graham said. "When you stall a system like this and it moves real slow, some of that rainfall can extend well away from the center."
A warm ocean is the fuel that powers hurricanes, and Florence will be moving over waters where temperatures are peaking near 30C, hurricane specialist Eric Blake wrote. 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 along with life-threatening freshwater flooding.
By noon EDT Monday, Florence had top sustained winds of 195kmh. It was centred about 1985km east-southeast of Cape Fear, North Carolina, and moving west at 20kmh. Its centre will move between Bermuda and the Bahamas today and tomorrow, and approach the coast of South Carolina or North Carolina on Thursday, the National Hurricane Center said.
Hurricane Isaac, meanwhile, was expected to lose strength as it reaches the Caribbean, and Helene, much farther out to sea, may veer northward into the open Atlantic as the 2018 hurricane season reaches its peak.
Preparations for Florence were intensifying up and down the densely populated coast. Since reliable record-keeping began more than 150 years ago, North Carolina has only been hit by one Category 4 hurricane: Hazel, with 209kmh winds in 1954.
The parking lot has been full for three days at the Ace Hardware store in coastal Calabash, North Carolina, where manager Tom Roberts said he sold 150 gas cans in two hours Monday, along with generators, plywood, rope, manual can openers, sand bags and a plethora of other items.
"I've been doing this since 1983," Roberts said as he completed an order for another 18-wheeler full of supplies. "This is the craziest one."
Many newcomers have moved to the coast in the nearly 19 years since the last strong hurricane - Floyd - threatened the area. Roberts said he's telling them to get out of town.
"I'm telling them to go inland, but I'm worried about the rain and tornadoes too," Roberts said.
Several meteorologists said Florence could do what Hurricane Harvey did over Texas, dumping days of rain, although not quite as bad.
"I think this is very Harvey-esque," said University of Miami hurricane expert Brian McNoldy. "Normally, a landfalling tropical cyclone just keeps on going inland, gradually dissipating and raining itself out. But on rare occasions, the steering patterns can line up such that a storm slips into a dead zone between troughs and ridges."
On North Carolina's Outer Banks, Dawn Farrow Taylor, 50, was yesterday gathering photos and important documents and filling prescriptions before heading inland. She grew up on the shore, and says this will be only the second time she's evacuated.
"I don't think many of us have ever been through a Category 4. And out here we're so fragile. We're just a strip of land - we're a barrier island. ... Already we're getting some overwash, the ocean is coming over 12," she said, referring to the islands' main road.
The governors of North and South Carolina and Virginia declared states of emergency far ahead of the approaching storm. South Carolina Governor Henry McMaster also suspended his campaign and asked US President Donald Trump for a federal emergency declaration.
Navy ships off Virginia's coast were preparing to sail out of the path, a North Carolina university has already canceled classes and people have begun stocking up on plywood, bottled water and other supplies.
Red flags have already been flying on beaches, warning swimmers to stay out of the water as seas began kicking up. People rushed to get emergency kits ready, map out escape routes, fill sandbags and secure their homes.
"Pretend, assume, presume that a major hurricane is going to hit right smack dab in the middle of South Carolina and is going to go way inshore," South Carolina Governor Henry McMaster said. The state's emergency management agency said it is "preparing for the possibility of a large-scale disaster."
In coastal Charleston, South Carolina, city officials offered sandbags to residents. Myrtle Beach Mayor Brenda Bethune urged people to secure their homes but said it was too early to know if evacuations will be ordered.
The University of North Carolina at Wilmington, near the shore, canceled its upcoming alumni weekend and all classes starting at noon Monday, encouraging its students to leave campus for a safer location.
In southeast Virginia, Naval Station Norfolk told not to leave their vehicles at the sprawling base later this week because of the flood threat. The Navy planned to send ships from the Hampton Roads area of Virginia out to sea.
Florida-based Carnival Cruise Line was re-routing its cruise ships, but there were other hurricanes to contend with.
Lining up behind Florence, Isaac was about 1855 kilometres east of the Windward Islands with top winds of 120kmh early yesterday, accelerating on a path to cross into the lower Caribbean Thursday as a weak hurricane.
Helene, meanwhile, was still in the Atlantic's spawning ground for hurricanes off the coast of Africa, swirling with 165kmh winds and forecast to become a major hurricane, about 600km west of the Cape Verde islands.