Florence crossed the 74 miles per hour threshold from tropical storm to hurricane Sunday morning, and by evening its winds were up to 85 miles per hour (140 kph) as the National Hurricane Center warned it was expected to become an extremely unsafe major hurricane by Monday and remain that way for days.
New National Hurricane Center reports show the track moving further west following landfall in North Carolina on Friday increasing impacts for the Palmetto state which include heavy rains, heavy wind and storm surge.
"All indications are that Florence will be an extremely risky Category 4 hurricane while it moves over the western Atlantic toward the southeastern United States", the hurricane center said.
At 5p.m. the center of Tropical Storm Isaac was located near latitude 14.5 north, longitude 36.6 west, moving towards the west near 7 miles per hour (11 kilometres per hour).
The National Hurricane Center said despite Florence eventual path, large swells will begin to affect the U.S. East Coast this weekend, resulting in life-threatening surfs and rip currents.
NOAA is predicting it will be at hurricane status on Sunday and a "dangerous major hurricane" by the time it reaches the coast later this week.
Helene was also upgraded to a hurricane on Sunday, the center said, but neither Helene nor Tropical Storm Isaac are expected to hit the mainland United States.
Florence became the first major hurricane of the 2018 Atlantic season this past Wednesday, reaching Category 4 status with maximum sustained winds peaking at 130 miles per hour. One year after historic storms that ravaged the American Gulf Coast and Puerto Rico last year, officials warned not to underestimate the threat the storm poses.
"The storm is strong and getting stronger", Cooper said.More news: Pittsburgh Steelers CB Joe Haden has mild hamstring pull
Helene will likely become a hurricane next week.
Florence's immediate threat for residents includes large ocean swells, unsafe rip currents and coastal flooding.
The three systems - Florence, Isaac and Helene - come right before the Atlantic hurricane season hits its peak Monday.
In coastal Charleston, South Carolina, city officials offered sandbags to residents.
Residents in North Carolina and other East Coast states should pay attention to the storm and begin to think about hurricane plans.
Rapidly intensifying Hurricane Florence could strike a direct and unsafe blow anywhere from the Carolinas to the Mid-Atlantic region later this week.
On Friday, North Carolina declared a state of emergency. Florence has been moving more toward the west and slightly northwest, potentially making direct landfall coming in from the east.