Since the hurricane has already amassed wind speeds of 130 miles per hour, the coast could see life-threatening wind, rain, and storm surges.
The NHC said Florence is 1,170 miles east-southeast of Cape Fear in North Carolina, moving west-northwest at 13 mph. A high-pressure ridge building to the north and northwest of Florence is expected to steer the hurricane west-north-westward to northwestward toward the southeastern US coast.
The storm "is too powerful and its path is too uncertain to take any chances", South Carolina Governor Henry McMaster said in issuing his state's emergency declaration. The move will allow the state to use the National Guard for preparations and recovery if necessary. "But we are not going to gamble with the lives of the people of SC".
"With Hurricane Florence on its way, we determined that this is the safest decision", Michael Glassner of the Trump Campaign said in a statement.
"There is an increasing risk of life-threatening impacts from Florence", the hurricane center has been saying for days.
Helene is a Category 2 storm that's even farther off the coast than both of the other storms, but it's not expected to ever make landfall.More news: Florence to become powerful hurricane Monday
By way of comparison, the maximum intensity of Hurricane Maria, the storm system which path of destruction left nearly 3,000 people dead in Puerto Rico, was 277.8 km/h, (150 knots), the NHC said.
Hurricane Helene is in the far eastern Atlantic Ocean and not expected to be near any land.
All eyes are on Hurricane Florence, now that it has intensified to a major Category 4 storm and is heading to the southeastern US coast. It was picking up speed over the Atlantic's warm waters, causing concerns about landfall and flooding from heavy rains afterward, possibly late Thursday or Friday.
In Virginia, home to the world's largest sea base, the United States navy has ordered all ships to sea in preparation for the storm, where they can more safely ride out the violent wind and waves. The state's emergency management division has posted additional information on the evacuations and how to prepare.
"Plan for the worst, pray for the best".
In coastal Charleston, South Carolina, city officials offered sandbags to residents.
While Guam is getting hit now with Typhoon Mangkhut and Hawaii is likely to get Tropical Storm Olivia tomorrow night, lets focus on the Atlantic, where three hurricanes have lined up. "Although Isaac is forecast to begin weakening when it approaches the Lesser Antilles, it is still expected to be at or near hurricane intensity when it reaches the islands".