"Rapid intensification is likely to begin by tonight", warned the latest advisory from the National Hurricane Center (NHC) in Miami, Florida.
The hurricane center said it was still too early to predict its exact path.
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.
Swells generated by Florence are affecting Bermuda and are beginning to reach portions of the US East Coast. It's also expected to strengthen, possibly becoming a hurricane by Monday.
Isaac has maximum sustained winds of 65 miles per hour (mph) and is moving toward the west near nine mph.More news: Heavy rain expected for Toronto starting Sunday night
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North Carolina Gov. Roy Cooper said in a statement Sunday that coastal and inland residents alike need to get ready for potentially heavy rainfall and flooding from the storm.
Tropical Storm Florence is quickly approaching the eastern United States, and according to the National Hurricane Center, the storm's threat to the East Coast keeps rising. Tropical storm force winds could be felt in Charlotte from this system.
A slew of risky storms - hurricanes, tropical storms and a typhoon - are now traveling over both the Atlantic and Pacific. For now, Isaac has 50 mph winds that extend 60 miles from its center.
Currently, there are no coastal warnings or watches for the storm.
The storm reached major hurricane status Wednesday, peaking with maximum sustained winds of 130 miles per hour (210 kph).
"It's important to remember the cone of uncertainty covers the entire SC coast, meaning landfall in SC is still a possibilty", Quagliariello said.
Forecasters said it is now around 1,500 miles east of the Windward Islands and is carrying winds of 65mph (100kph).
Isaac will be near the Lesser Antilles later this week and could bring impacts to parts of the Caribbean Islands during this time frame.