Florence, the most powerful storm to menace the USA 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.
The NHC expects the hurricane's winds to strengthen to 130 miles per hour as it moves east by Tuesday, drawing energy from the warm water.
The National Hurricane Center also warned that Florence could cause life-threatening surf and rip currents along the East Coast, from Florida to North Carolina.
As of 5 p.m. ET Monday, the center of Florence was located about 1,170 miles from Cape Fear, North Carolina, and was moving to the west-northwest at 13 mph.
A Category 4 hurricane with 130 miles per hour winds is bearing down on the US East Coast, bringing a risk of devastating floods.
Large swells are already affecting Bermuda and parts of the U.S. East Coast, according to the NHC.
By the time it reaches the USA mainland, the NHC says Florence will strengthen into "an extremely unsafe major hurricane".
South Carolina Governor Henry McMaster warned residents to prepare for possible evacuations and he even called on President Donald Trump to declare a federal emergency in the state to prepare for the impact of the storm.
The Carolina coast needs to brace for impact Thursday and Friday.
Preparations for Florence were intensifying up and down the densely populated coast.
"The bottom line is that there is increasing confidence that Florence will be a large and extremely risky hurricane, regardless of its exact intensity, " Blake said.
"We have already began mobilizing our assets to respond accordingly, and we are here for you!"
North Carolina Governor Roy Cooper said in a statement on Sunday: "Review your emergency plans and gather your supplies now".
On Monday Florence had strengthened into a category 4 hurricane.
Astronaut Ricky Arnold captured this image of Hurricane Florence from the International Space Station on Monday, September 10, 2018. This could be a very unsafe situation for them. After passing the Cabo Verde Islands the system was not expected to pose a direct threat to land for at least several days. We will have to continue to see how the next few advisories trend in order to have a better idea.
Cooper and his counterparts in neighbouring SC and Virginia ordered about 1 million people to evacuate coastal homes, including along the Outer Banks barrier islands.
Behind Hurricane Florence, Hurricane Isaac and Hurricane Helene are both swirling in the Atlantic.
Hurricane Florence is now a Category 2 storm and is still forecast to slam into the southeastern United States.
NOAA Hurricane Florence is forecast to hit the northeast coast later this week.
Isaac is expected to gain strength in the next day or two before beginning to weaken mid-week when it approaches the Lesser Antilles.