Florence, the most powerful storm to menace the US mainland this year, intensified into a Category 4 hurricane as it howled closer to the Carolinas on Monday, prompting evacuations of more than 1 million people to higher ground.
Storm surge and hurricane watches may be issued Tuesday morning for portions of southeastern U.S. states, the NHC said.
The hurricane, which is now whipping up winds at 130 miles per hour, is a Category 4 storm and forecast to make landfall later this week on the coast of the Carolinas.
As of 5 a.m., Florence was centred about 625 miles southeast of Bermuda, moving west at 9 miles per hour.
"There is an increased risk of two life-threatening impacts from Florence: storm surge from the coast and freshwater flooding from a prolonged heavy rainfall inland".
"It's an extremely unsafe, life-threatening, historic hurricane. the forecast shows Florence stalling over North Carolina, bringing days and days of rain".
Florence expected to become hurricane, head to southeast US
The state Emergency Management Division said residents should begin preparing their homes and property for the storm. Chris Knox told NPR, "This allows our farmers to gather their crops, and get these crops out ahead of the storm".
Trump said in a Twitter message he has spoken to the governors of North and SC and Virginia, adding: "Federal government stands by, ready to assist".
"Pretend, assume, presume that a major hurricane is going to hit right smack dab in the middle of SC and is going to go way inshore", McMaster said in a press conference.
"The storm is strong and getting stronger", Cooper said.
"Florence has continued to rapidly strengthen", the NHC said at 1500 GMT.
"We do not know what the chances are that it will hit us or if so, what kind of blow or where and we don't know precisely when", said South Carolina Gov. Henry McMaster".
At a press conference on Monday, Cooper called his state the "bullseye" for Hurricane Florence, saying they are "bracing for a hard hit". "We are in a very deadly and important game of chess with Hurricane Florence".
The NHC also says the storm could become more powerful.
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Although the path of the Hurricane remains unclear, the center is warning people to "closely monitor the progress of Florence, ensure they have their hurricane plan in place and follow any advice given by local officials".
The hurricane center's description of a Category 4 hurricane begins with "catastrophic damage will occur".
Behind Hurricane Florence, Hurricane Isaac and Hurricane Helene are both swirling in the Atlantic.
National Hurricane Center Director Ken Graham warned that Florence was forecast to linger over the Carolinas once it reaches shore. After passing the Cabo Verde Islands the system was not expected to pose a direct threat to land for at least several days.
The US Navy said it was preparing to send about 30 ships stationed in Virginia out to sea.
AccuWeather meteorologist Brett Rossi said the ground in North and SC and Virginia is already saturated from recent rains.
In addition, in the Pacific, what's now Hurricane Olivia is forecast to approach Hawaii as a tropical storm on Tuesday.
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