"We expect a rapid intensification of Florence tomorrow", Dennis Feltgen, a spokesman for the National Hurricane Center, said on Sunday.
Meanwhile, the two other tropical storms in the Atlantic - Florence and Helen - are expected to become hurricanes today. "It's going to go inland, sit over the southern Appalachians and lead to 3-4 feet of rain, in parts of South Carolina, North Carolina, perhaps even into southwest Virginia", he says.
This is the most powerful storm to take aim at the USA. mainland this year and could be upgraded to a Category Five with winds higher than 157mph.
Where is the hurricane now?
Florence was 575 miles (925 kilometers) south-southeast of Bermuda and the center of the hurricane was forecast to pass between Bermuda and the Bahamas on Tuesday and Wednesday, the NHC said. Drawing energy from the warm water, the now Category 2 storm could be a fearsome Category 4 with winds of 130 miles per hour (209 kph) or more by Tuesday.
The NHC issued a warning Monday morning, explaining when powerful gusts may approach.
Hurricane-force winds extend outward up to 10 miles (20kilometers) from the center and tropical-storm-force winds extend outward up to 45 miles (75 kilometers).
What else should I know?
The storm has prompted the governors of North Carolina, South Carolina and Virginia to each declare state of emergencies in their states.
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"Already we're getting some overwash, the ocean is coming over 12", she said, referring to the islands' main road.
Hurricane Isaac is holding steady in strength over the Atlantic. Category 3 storms are considered major hurricanes that could inflict "devastating damage", says the center. We're just a strip of land - we're a barrier island.
Forecasters said their hurricane hunter aircraft found Florence strengthening as it churned about 1,160 kilometres southeast of Bermuda. There is the added possibility that the storm will slow after landfall, bringing sustained torrential rainfall and the potential for catastrophic flooding.
Interests from SC through coastal Virginia should continue to pay close attention to future forecasts.
"This is a very unsafe hurricane", Governor Henry McMaster has said.
The US military said it was sending an advanced team to Raleigh, North Carolina, to coordinate with federal and state partners and that about 750 military personnel will be designated to provide support.
The 2018 hurricane season lasts until November 30.
As of early Monday, the storm was getting stronger, with maximum sustained winds of 105 miles per hour.