"While Florence has weakened below major hurricane intensity, the wind field of the hurricane continues to grow in size", the NHC said in its latest bulletin. Unfortunately, the heavy rainfall is not restricted to coastal Carolina.
In addition to being the deadliest threat, storm surge is also typically the most destructive part of a hurricane.
Another 25 percent of deaths are related to rain, he said.
In neighbouring Maryland, Governor Larry Hogan said his state was readying for potentially "historic and catastrophic rainfall, life-threatening flooding, and high winds". All lanes of Interstate 26 are westbound to allow more people to leave the coast and head inland toward the state capital of Columbia. "Our farmers take hurricane threats extremely seriously".
Some 7,000 guard members are ready to mobilize in North Carolina, while 1,100 will be activated in SC.
"This storm is big and it's vicious", North Carolina Governor Roy Cooper said on NBC's "Today" Show on Wednesday.
SC authorities reported one death.
At the White House, President Donald Trump both touted the government's readiness and urged people to get out of the way of Florence.
Trump, who plans a visit to the region next week, tweeted his "deepest sympathies and warmth" to the families and friends of those who had lost their lives.
As of Wednesday afternoon, Florence is a powerful Category 3 storm with maximum sustained winds of about 125mph as it continued on its path toward the Carolinas Wednesday.
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At the same time, employment fell in information, culture and recreation, and business, building and other support services. This marked the seventh straight month the unemployment rate was below five per cent, normally a sign of a healthy economy.
Updated NHC forecasts showed the storm lingering near the coast, bringing days of heavy rains that could bring intense inland flooding from SC, where some areas could see as much as 40 inches (1m) of rain, to Virginia. "Heed those warnings and evacuate if you're in one of the zones".
"The worst is yet to come", he added.
A Hurricane Warning has been issued for Myrtle Beach, South Carolina. At 8 a.m. (1200 GMT) on Wednesday the storm was located about 530 miles (855 km) southeast of Cape Fear, North Carolina.
On Saturday, its streets were strewn with downed tree limbs and carpeted with leaves and other debris.
Duke Energy, the nation's No. 2 power company, said Florence could knock out electricity to three-quarters of its 4 million customers in the Carolinas, and outages could last for weeks. In North Carolina, Cooper says, "2,800 soldiers will be on active duty, joined by even more on standby".
This means Florence could hover over the southeast states, pouring risky rainfall causing flash flooding and river flooding - some areas are forecast to get from 15 to 20 inches to 30 inches or more localized areas.
To "err on the side of caution", County Council Chairman Vic Rawl told Fox News the county previously entered into an intergovernmental agreement with neighboring Berkeley, Dorchester and Orangeburg Counties to use shelters - including a few established pet-friendly places - if necessary. Thousands of marines and their families evacuated from Camp Lejeune, leaving the rest to dig in ahead of what could be a direct hit. "If we try to leave, we'll just get stuck in the rain".
The winds cover an area more than 53,000 square miles - which is larger than the entire state of North Carolina.
As the United States dealt with Florence, a strong typhoon tore across the northern tip of the Philippines, wrecking homes and triggering landslides before heading toward Hong Kong and China.