Florence, now a Category 4 storm with sustained winds of 130 miles per hour (209 km/h), was previously expected to travel north, up the North Carolina coast, after making landfall, according to the statement.
The hurricane's immensity is why some 10 million people across North Carolina, South Carolina and Virginia are under storm watches and warnings, with meteorologists projecting Florence could become the most powerful storm to hit this part of the United States in at least 25 years.
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Sib McLellan, left, and his wife, Lisa, prepare for Hurricane Florence.
In Wilmington, North Carolina, which is one of the areas where Florence may make landfall, NOAA tidal data shows a sea level rise of around 20cm (0.7 feet) since 1930s, meaning the storm surge will be higher and impacts greater than otherwise.
Florence's intensity has diminished since it roared ashore along the US mid-Atlantic coast on Friday as a hurricane.
Florence has already set a North Carolina record for rainfall totals, exceeding that of Hurricane Floyd, which struck in 1999 and caused 56 deaths.
Their entire neighborhood evacuated in Wilmington, North Carolina, David and Janelle Garrigus planned to ride out Florence at their daughter's one-bedroom apartment in Charlotte.
The Barbados Meteorological Services continues to closely monitor the progress of Tropical Storm Isaac over the Atlantic.
Relentless rain threatens North Carolina agricultural town
The operations were made more perilous by fallen trees and power lines; officials didn't expect power to be restored for weeks. One was electrocuted while hooking up a generator and the other while checking on his dogs outside, emergency officials said.
As of 11 p.m. EDT Wednesday, the storm was centered 260 miles (455 kilometers) east southeast of Wilmington, North Carolina, moving northwest at 17 mph (28 kph).
Georgia Governor Nathan Deal declared a state of emergency "in light of the storm's forecasted southward track after making landfall".
The East Coast isn't the only area facing the brunt of a storm.
As of Wednesday night, Florence's tropical storm force winds were almost 400 miles wide - or the roughly the equivalent of driving from Washington, D.C, to Charlotte, North Carolina; or from Milwaukee, Wisconsin to St. Louis; or from Los Angeles to San Francisco.
In Fayetteville, a North Carolina city of about 210,000 people about 90 miles inland, authorities told thousands of residents near the Cape Fear River and Little River to get out of their homes by Sunday afternoon because of the flood risk.
Nurse Barbara Mack was using a small shovel to fill sandbags at a public works facility in Charleston, but she saw a silver lining in the hurricane preparations.
SC ordered the mandatory evacuation of one million coastal residents while North Carolina ordered an evacuation of the Outer Banks, barrier islands that are a popular tourist destination.
Interestingly, the Atlantic Ocean housed three hurricanes at the same time, that before Tropical Storm Isaac being downgraded from its former hurricane status.