Customers line up to buy propane at Socastee Hardware store, ahead of the arrival of Hurricane Florence in Myrtle Beach, South Carolina, on September 10, 2018. (REUTERS/Randall Hill)
At this height of the Atlantic hurricane season, Florence was being trailed on east-to-west paths by two other hurricanes, Helene and Isaac.
Helene -- 375 miles (600km) west of the Cape Verde islands off the African coast -- had winds up to 105mph (165kph), and was expected to continue moving west-northwest for another couple of days, the NHC said in its 1500 GMT bulletin.
Hurricane Isaac -- which late Sunday became the fifth hurricane of the season -- is heading west towards the Caribbean.
At 1500 GMT, Isaac, which the NHC called a small hurricane, was about 1,150 miles (1,855km) east of the Windward Islands -- a region still recovering from last year's powerful Hurricane Maria -- with maximum sustained winds near 75mph (120kph).
Maria -- which killed at least 3,057 people, most in Puerto Rico -- is believed to be the third-costliest tropical cyclone on record.
The costliest hurricane in US history, Katrina was a Category 3 storm when it made landfall on the Gulf Coast in August 2005 -- claiming an estimated 1,833 lives.