Two active hurricanes - Florence and Helene - were also moving across the Atlantic Tuesday.
Forecasters at the University of MI predict that 2.4 million people will lose power from Hurricane Florence and some outages could be prolonged.
The National Hurricane Center downgraded Isaac to a tropical storm overnight but said Tuesday that it could be "at or near hurricane levels" on Thursday, when it approaches the Lesser Antilles Islands.
Walker Townsend, right, from Isle of Palms, S.C., fills a sand bag while Dalton Trout, center, holds the bag at the Isle of Palms municipal lot where the city was giving away free sand in preparation for Hurricane Florence, Monday, Sept. 10. "Swells will remain very rough to the south and east for Wednesday while gradually shifting southerly as Florence moves away to our southwest". "All you have to do is look up at your ceiling, and think about 12 feet (of water)".
North Carolina Gov. Roy Cooper called the storm a "monster".
Hurricane-force winds extend outward up to 35 miles (55 km) from the center and tropical-storm-force winds extend outward up to 115 miles (185 km).
Meanwhile, Hurricane Florence was 580 miles south, south east of Bermuda with winds of 115 mph and strengthening into a major storm. This could lead to historic flooding along the coast.
High winds, storm surge and coastal flooding will be an issue for the Carolina coastlines.
Florence's center is located roughly 750 miles southeast of the North Carolina, and SC border at the coast.
Hurricane conditions are possible within the hurricane watch area - Guadeloupe, Martinique and Dominica - by Thursday morning, with tropical storm conditions possible early Thursday in both the tropical storm watch area - Antigua, St Kitts and Nevis, and Montserrat - and the hurricane watch areas, the NHC added.
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This storm is lined up behind Florence in the Atlantic.
By the time it moves through the central Lesser Antilles, Isaac is expected to be near hurricane strength before weakening on Friday.
Sustained winds have reached nearly 105 miles per hour.
"A high pressure system, known as a Bermuda high has been in place, forcing Florence to take a path south and west of what we typically see", Klotz said.
Some areas could exceed 30 inches of rain from the storm.
Many newcomers have moved to the coast in the almost 19 years since the last strong hurricane - Floyd - threatened the area.
However, Hubbard said Florence is not expected to have any impact on Canada, given its predicted track into the USA mainland, where it will likely weaken considerably on the weekend.
In the village of Buxton, Liz Browning Fox plans to ride the storm out in her house on top of a ridge.
South Carolina Gov. Henry McMaster said an estimated 1 million people would be fleeing his state's coast, with eastbound Interstate 26 heading into Charleston and US 501 heading into Myrtle Beach reversed to ease the exodus.
"You never know, there could be tree missiles coming from any direction", she said.