'Staggering' Hurricane Florence On Collision Course For Carolinas

RALEIGH, N.C.  (CBS) -- With mandatory evacuations already issued for parts of three East Coast states, millions of Americans are preparing for what could become one of the most catastrophic hurricanes to hit the Eastern Seaboard in decades. Sustained winds were 130 mph Tuesday morning, but it remains a Category 4 storm and is expected to intensify to near Category 5 status as it slows over very warm ocean water near North and South Carolina.

Update from National Hurricane Center at 4 p.m.:

Hurricane Florence's size is "staggering," National Hurricane Center Director Ken Graham warned.

"We could cover several states easily with the cloud cover alone," Graham said. "This is not just a coastal event."

The center of the massive storm is forecast to make landfall along a stretch of coastline already saturated by rising seas and then meander Thursday, Friday and Saturday, inundating several states and triggering life-threatening floods. Seven-day rainfall totals are forecast to reach 10 to 20 inches over much of North Carolina and Virginia, and even 30 inches in some places. Combined with high tides, the storm surge could swell as high as 12 feet.

"The water could overtake some of these barrier islands and keep on going. With time, the wind pushes the water into every nook and cranny you can think of," Graham said. "All you have to do is look up at your ceiling, and think about 12 feet (of water). That, folks, is extremely life-threatening."

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The storm's first effects were already apparent on barrier islands as dangerous rip currents hit beaches and seawater flowed over a state highway -- the harbinger of a storm surge that could wipe out dunes and submerge entire communities. Watches were in effect Tuesday for a storm surge that could reach up to 12 feet at high tide on a stretch from Cape Fear to Cape Lookout in North Carolina, forecasters said.

A hurricane watch was in effect for Edisto Beach, South Carolina, to Virginia's southern border, and the first hurricane-force winds arriving late Thursday.

"Please be prepared, be careful and be SAFE!" President Donald Trump tweeted Monday evening. He has declared states of emergency for North and South Carolina ahead of the storm, which frees up help from federal agencies.

South Carolina's governor ordered the state's entire coastline to be evacuated starting at noon Tuesday and predicted that 1 million people would flee. CBS News correspondent David Begnaud reported that lanes, at noon, will be reversed on four of the largest roads leading to the South Carolina coast, so cars will only be able to drive inland.

Similar evacuations are happening all the way up to Virginia, where the governor has ordered a mandatory evacuation for residents of some low-lying coastal areas.

For many people, the challenge could be finding a safe refuge: If Florence slows to a crawl just off the coast, it could bring torrential rains to the Appalachian mountains and as far away as West Virginia, causing flash floods, mudslides and other dangerous conditions.

On Tuesday, Washington D.C.'s mayor, Muriel Bowser, declared a state of emergency in the District ahead of the hurricane, effective immediately. On Monday, Maryland Gov. Larry Hogan declared a state of emergency for the state.

North Carolina Gov. Roy Cooper said his state was "in the bullseye" of the storm and urged people to "get ready now." The very center of that bullseye may be Camp Lejeune, the sprawling Marine Corps training base, where authorities were opening emergency operation centers, staging equipment and urging families on the base to build survival kits with food and equipment needed to sustain themselves for 72 hours.

Mandatory coastal evacuations were in effect for civilians in South Carolina, North Carolina and Virginia, but the military base posted on Facebook that different chains-of-command would decide whether to release non-essential personnel, and some relatives vented fears that they wouldn't be able to evacuate in time.

The storm's potential path also includes half a dozen nuclear power plants, pits holding coal-ash and other industrial waste, and numerous hog farms that store animal waste in massive open-air lagoons.

Airlines, including American and Southwest, have started letting passengers change travel plans that take them into the hurricane's possible path.

Preparations for Florence were intensifying up and down the densely populated coast. 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.