Rapidly intensifying Hurricane Florence could strike a direct and dangerous blow anywhere from the Carolinas to the Mid-Atlantic region later this week. Florence crossed the 74 mph threshold from tropical storm to a hurricane on Sunday morning, and by evening its winds were up to 85 mph as the National Hurricane Center warned a hurricane hunter plane found the storm strengthening quickly.

Forecasters said Florence was expected to become an extremely dangerous major hurricane sometime Monday and remain that way for days.

As of 5 a.m. EDT, Florence was centered about 625 miles southeast of Bermuda, moving west at 9 mph. Its maximum sustained winds were at 105 mph. Drawing energy from the warm water, it could be a fearsome Category 4 with winds of 130 mph or more by Tuesday, the Miami-based center said.

The center also said that Hurricane Isaac had become the 5th named hurricane of the 2018 Atlantic season.

Isaac was about 1,230 miles east of the Windward Islands with maximum sustained winds of 75 mph early Monday. The storm was moving west at 13 mph and expected to accelerate over the next 36 hours. It poses no threat to land at this time, the center said.

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An infrared satellite image provided by the National Hurricane Center shows Hurricane Florence churning in the Atlantic early on the morning of Sept. 10, 2018. NOAA/NWS/NATIONAL HURRICANE CENTER

Forecasters said it is too early to know the exact path Florence will take but warned that it could roll ashore in the Carolinas by Thursday. But authorities were taking no chances as the governors of North and South Carolina and Virginia declared states of emergency far ahead of the approaching storm.

People in Wilmington, North Carolina, were stocking up on water, plywood and generators to prepare for the storm, CBS News correspondent David Begnaud reports. Some store shelves were already empty.

Florence could be the first major hurricane to slam North Carolina dead-on since Fran hit as a Category 3 in 1996. Fran toppled homes and businesses across the state.

Fran caused more than $8 billion in damage. Thirty-seven people were killed.

"These storms are catastrophic events," said Andrew Wunderley, who works for a water-conservation group in South Carolina. He said the low-lying cities on the coast are particularly vulnerable to flooding.

"I think what we found is that we're not really that prepared for these events," Wunderley said. In October 2015, a storm system caused 36 dams to fail across South Carolina, resulting in what was called a "thousand-year flood."

At least 25 people died. If Florence ends up stalling after it makes landfall in the southeastern U.S., the fear is that could happen again.

In Virginia, Navy ships off the coast were getting set to sail out of the path of the powerful hurricane, one North Carolina university canceled classes and people have begun stocking up on plywood, bottled water and other supplies even with Florence still far out at sea southeast of Bermuda.

People up and down the densely populated coast were told to be ready for the worst -- and not just for a possible direct blow against the coast. They warned that Florence could slow or stall on or near shore, with some forecasting models showing it could unload a foot or two of rain in places, causing devastating inland flooding.

"What that means is not only do we have a serious, 130 mph potential wind threat at landfall along with catastrophic storm surge, but also a very large inland flood threat that could include two feet of rain in certain spots including inland North Carolina's most populous cities," CBS News meteorologist David Parkinson said late Sunday. "The most important takeaway out of the storm is that this will not be a quick hitting major storm but a long duration one. We will likely be talking about this actively raining at this time next week. Pace yourselves. It's gonna be a long one."

Forecasters have warned of a rising threat of life-threatening storm surge, along with the damage of a hurricane's high winds.

Red flags flying on beaches warned swimmers to stay out of waters as seas began kicking up. People rushed to get emergency kits ready, map out escape routes and 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 Charleston, South Carolina, along the coast, 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 officials started getting bulldozers and chain saws ready.

In Jacksonville, North Carolina, about 20 miles from the coast, 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.

As Hurricane Florence approaches the East Coast, the University of North Carolina at Wilmington canceled classes and encouraged its students to leave campus for a safer location.

In southeast Virginia, Naval Station Norfolk told its employees they should not leave their vehicles parked at the sprawling base in coming days 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 re-routed its cruise ships.

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