Since reliable record-keeping began more than 150 years ago, North Carolina has only been hit by one Category 4 hurricane: Hazel, with 130 mph winds in 1954.
"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 Gov. Henry McMaster also suspended his campaign and asked 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 Gov. 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.
Myrtle Beach hardware stores and supermarkets were busy ringing up sales of bottled water, plywood and generators.
"Literally, they are filling buggies full of water, shopping carts full of water," Ryan Deeck, grocery department manager at a Walmart, told The Sun News. "They're coming in and buying water and plates, and that's about all they're buying."
North Carolina crews were getting bulldozers and chain saws ready.
In Jacksonville, North Carolina, about 20 miles (32 kilometers) inland, some residents picked up hurricane supplies during their normal weekend shopping, The Daily News reported. Ilija Cesal told the newspaper he wouldn't worry about buying extra water or other supplies for a few more days.
"I'll see by Wednesday how that goes — we got over 48 hours before that happens," Cesal said.
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 1,150 miles (1,855 kilometers) east of the Windward Islands with top winds of 75 mph (120 kph) early Monday, moving west at 14 mph (22 kph). Isaac's forward movement was accelerating on a path to cross into the lower Caribbean on Thursday.
Helene, meanwhile, was still in the Atlantic's spawning ground for hurricanes off the coast of Africa, swirling with 105 mph (165 kmh) winds and forecast to become a major hurricane, about 375 miles (600 kilometers) west of the Cape Verde islands.
Associated Press contributors include Jennifer N. Kay in Miami; Jeffrey Collins and Meg Kinnard in Columbia, South Carolina; and Jeffrey Martin in Atlanta.
Reuters contributed to this report.