The National Hurricane Center says it is still too early to predict the hurricane's exact path, but a huge coastal area from northern Florida to North Carolina should prepare for a major hit.
Dare County officials have announced that a mandatory evacuation order goes into effect on Hatteras Island at noon Monday.
"We are in the bull's-eye", North Carolina Governor Roy Cooper said at a news conference.
North Carolina has a strong statute against price gouging - charging too much during a time of crisis - that is tied directly to a declaration of a state of emergency. As it nears the USA coast, winds speeds could rise and fall as the intense storm undergoes eyewall replacements, broadening the storm and increasing the areas potentially impacted.
The latest measurement of Hurricane Florence show maximum sustained winds of 140 miles per hour.
Florence crossed the 74 miles per hour threshold from tropical storm to a hurricane Sunday morning, and by evening its winds were up to 85 miles per hour (140 kph) as the National Hurricane Center warned a hurricane hunter plane found the storm strengthening quickly.
Florence's effects were already being felt along the coast, with risky swells and rip currents in some spots.
"These swells are likely to cause life-threatening surf and rip current conditions", the center said. Regardless of where Florence comes near land, its impact, including wind, rain, and storm surge, will be felt well outside the immediate area near storm's center. "This storm gets stronger and stronger" and is on its way to a head-on impact on the Carolinas, CNN meteorologist Chad Myers said.
Henry McMaster has ordered the evacuation to start at noon Tuesday as Hurricane Florence approaches.
Because the storm is so small, forecasters are less certain about how intense Isaac may become.
The governors of North and SC and Virginia declared states of emergency far ahead of the approaching storm. The forecast track has the storm strengthening to a hurricane next week as is tracks west.
Tropical Storm Florence has sustained winds of 70 mph Saturday evening as it is located 810 miles southeast of Bermuda.
A high pressure system building to the northwest is expected to steer Florence over the next few days across the Atlantic as it picks up speed.
Foremost among those is Tropical Storm Florence, which is expected to re-strengthen into a hurricane Sunday and looks increasingly likely to hit the East Coast. The hurricane could make landfall possibly as a Category 3 or higher on the five-step Saffir-Simpson scale.
Last week, Florence became the first major hurricane of the 2018 Atlantic season.
Olivia is expected to move west through Monday before turning west-southwest late Monday and early Tuesday local time.
"This is going to be big", said Victoria Oliva, a meteorologist with the National Weather Service in Wilmington. Most of the models are now showing Florence having a direct and major impact to the East Coast in the upcoming week. An Ohio Valley ridge is then expected to slow the storm is it nears the coast. "People in SC in North Carolina particularly should prepare for the storm because any change in forward heading would close the window of opportunity quickly".
The current forecast track predicts that Florence will approach the southeast US coast on Thursday.
As of 11 p.m. EDT, Florence was centered about 685 miles (1,100 kilometers) southeast of Bermuda, moving west at 7 mph (11 kmh). A westward motion with a slight increase in forward speed is expected through the end of the week.
Tropical-storm-force winds could reach the coastline as early as Wednesday night, at which point all outdoor preparations should be completed.
The estimated minimum central pressure is 993 mb (29.33 inches).
Behind Isaac, Helene has strengthened with maximum sustained winds estimated to be at 105 miles per hour with higher gusts.
Forecasters said Florence could become an extremely unsafe major hurricane sometime Monday and remain that way for days.