Florence's top sustained wind speeds dropped from a high of 140mph to 110mph which reduced the hurricane's power from Category 4 to Category 2.
"The big picture: There are several characteristics of the changing climate that are helping to increase the risks of damage from Hurricane Florence, even though global warming is not directly causing such a storm to spin up".
Emergency workers monitor hurricane progress at the Emergency operations centre in Wilmington, North Carolina.
Officials said some 1.7 million people in the Carolinas and Virginia were warned to evacuate, but it is unclear how many did. Parts of North Carolina could get 1m of rainfall.
"This will likely be the storm of a lifetime for portions of the Carolina coast", the National Weather Service in Wilmington, N.C., said, "and that's saying a lot given the impacts we've seen from hurricanes Diana, Hugo, Fran, Bonnie, Floyd, and Matthew".
Coastal residents are not the only people attempting to move out of harm's way of Hurricane Florence.
"This is going to be a Mike Tyson punch to the Carolina coast", said Jeff Byard, the associate administrator for response and recovery at the Federal Emergency Management Agency (FEMA).
Amanda Kinseth, reporter for WPDE ABC 15 News in Myrtle Beach, South Carolina.
Florence isn't the only one. There are more hurricanes brewing
The Dare County Commission ordered evacuations of Hatteras Island, also part of the Outer Banks, on Monday and Tuesday. As of noon Tuesday, lanes will reverse on Interstate 26 from Charleston to Columbia and US 501 from Myrtle Beach.
Justin Rose savours world No 1 status after runner-up finish
Rose ascended to the No. 1 ranking in the Official World Golf Rankings and became just the 22nd golfer in history to do so. It's tough to go from being on Ryder Cup teams, being on Presidents Cup teams, to outside the top 100 in the world.
Hurricane Florence looks absolutely wild from the International Space Station
The state's emergency management division has posted additional information on the evacuations and how to prepare. Hurricane Helene will likely continue to strengthen since it is in a low wind shear environment and warm waters.
"I'm scared we'll get 30 inches or more of rain", said Carol Trojniar, 69, a longtime Wilmington resident and retired real estate agent who has never experienced a Category 4 hurricane.
Henry McMaster lifted the mandatory evacuation order for Beaufort, Jasper and Colleton counties Tuesday morning.
Emergency preparations in the area included activating 2,800 National Guard troops in North Carolina, stockpiling food, setting up shelters, switching traffic patterns so that major roads led away from shore and securing 16 nuclear reactors in the three-state region.
Florence is now heading for ocean water that has surface temperatures of about 85 degrees, meaning it will most likely strengthen on its way to the East Coast.
"This storm is a monster", North Carolina Governor Roy Cooper said.
Officials in New Bern, which dates to the early 18th century, said more than 100 people were rescued from floods and the downtown was under water by Friday afternoon.
The NHC said the first tropical storm-force winds of at least 39mph (63 kph) would hit the region early on Thursday with the storm's centre reaching the coast Friday. The storm's forecast has shifted southward in the last 24 hours.
Its surge could cover all but a sliver of the Carolina coast under as much as 11ft of ocean water, and days of downpours could unload more than 3ft of rain, touching off severe flooding.
U.S. President Donald Trump on Twitter warned of the storm's dangers and praised his administration's handling of past hurricanes, rejecting criticism for its response to Hurricane Maria previous year in Puerto Rico.