Florence intensified into a hurricane on Sunday and was expected to strengthen rapidly as it churned across the Atlantic Ocean and threatened to make landfall on the U.S. East Coast by the end of the week.
The storm's sustained winds reached 75 mph (121 kph), just over the threshold for a hurricane, on Sunday morning as it was moving across the Atlantic, about 750 miles (1,210 kilometres) southeast of Bermuda.
According to the National Hurricane Center's 5:00 p.m. advisory, the center of Tropical Storm Isaac was located near latitude 14.5 North, longitude 40.3 West. Isaac is moving toward the west near 12 mph (19 km/h) and is expected to accelerate during the next 36 hours. It was moving west at 6 miles per hour. Drawing energy from the warm water, it could be a fearsome Category 4 with winds of 130 miles per hour (209 kph) or more by Tuesday, the Miami-based center said.
The NHC in Miami said it is expected to develop into a major storm.
Right now, the latest forecast from the National Hurricane Center has Hurricane Florence becoming a "major hurricane" sometime Monday.
The National Weather Service has also issued a typhoon watch in the USA territory of Guam, where Tropical Storm Mangkhut is approaching from the east and is expected to bring damaging winds by Monday evening.
The University of North Carolina Wilmington has issued a voluntary evacuation order for students starting noon Monday due to potential impacts from Hurricane Florence.
Officials in the Carolinas warned residents to prepare and to brace for impact.
Forecasters said it was too soon to determine the exact timing, location and magnitude of storm surges and flooding Florence will cause.
Swells generated by Florence are affecting Bermuda and could cause risky rip currents and coastal flooding Saturday in areas including coastal DE and New Jersey, the National Weather Service said.
After 2016's Hurricane Matthew devastated inland areas of the state, Cooper said people need to be prepared for inland flooding from heavy rain.
Loewenthal said the area should prepare to see impacts, including rough surf and risky rip currents, as early as Sunday.
A tropical storm warning and hurricane watch are in effect for the Cabo Verde islands of Santiago, Fogo, and Brava. The storm is expected to continue on its westward path.