Map shows probable path of Hurricane Florence.
The NHC said the first tropical storm-force winds of at least 39 miles per hour (63 kph) would hit the region early on Thursday with the storm's centre reaching the coast Friday.
North Carolina Governor Roy Cooper warned that staying put would be a grave mistake and said people in evacuation zones "need to get out now".
The pivot in the forecasted track of Florence led Georgia's governor to declare a state of emergency for all 159 counties, home to 10.5 million people.
The president signed emergency declarations for the Carolinas and Virginia, a move that frees up federal money and resources.
The National Hurricane Center expects Florence's rainfall totals to be around 40 to 60 centimeters, with some areas receiving as much as 90 centimeters of rain. "With more than 300 miles of coastline in the path of the storm, it's important for [companies] like U-Haul to do what they can".
"We may not even get the worst of it until Saturday", Sharp said.
"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". "So this is not just going to be a coastal threat". Even if you've ridden out storms before, this one is different. Hurricanes Irma and Maria struck the island in September 2017, the latter of which had its official death toll increased last month from 64 people dead to 2,975.
Residents in some parts of the Carolinas have been ordered to evacuate.
"This is a real hurricane that we have coming and our goal is to protect lives and property", said Steve Goldstein, NOAA liaison to FEMA.
"This will be a storm that's going to be far larger than we have seen in perhaps decades", Trump said.
According to Fox News Senior Meteorologist Janice Dean, Florence could stall upon reaching the Carolina coast later this week and make a slight shift south toward SC once it makes landfall, becoming "a major flooding event".
Experts say this could be the strongest storm to hit the Carolina coast in more than 60 years. A tropical storm watch was also in effect for parts of Virginia.
"This is going to produce heavy rainfall, and it may not move very fast", Craig Fugate, former director of the Federal Emergency Management Agency, previously said.
The storm's 175-mile (282 km) wide "cone of probability" suggests the storm will likely hit North Carolina's coast near Cape Fear, but storms fall outside the cone one-third of the time, according to The Weather Channel.