"Florence is forecast to be a unsafe major hurricane near the southeast US coast by late next week, and the risk of direct impacts continues to increase", the hurricane center said Saturday.
Meantime the NHC said Tropical Storm Florence is now "a little stronger" and is expected to become a hurricane again tonight or early Sunday.
Florence continues to defy easy prediction, but the latest projection is landfall in the Wilmington area at 2 a.m. Friday, but the Carolinas will feel the storm far in advance of that, NOAA is predicting.
It was centered about 1,230 miles east-southeast of Cape Fear, North Carolina, and moving west at 13 mph. This, unfortunately will mean that Florence has a much higher chance of affecting the USA east coast by later in the week. They were likely to cause life-threatening surf and rip current conditions, according to the NHC.
Isaac was about 1305 miles east of the Windward Islands with maximum sustained winds of 75 mph late Sunday. Hurricane-to-tropical-storm-force winds could extend inland, depending on the storm's track.
Experts have warned for years of the danger hurricanes pose to a region stretching from Virginia Beach at the mouth of the Chesapeake Bay to Charleston, South Carolina, where the land is sinking and the ocean is rising at some of the highest rates on the East Coast. Isaac, which was moving toward the lesser Antilles in the Caribbean Sea, could bring heavy rain and become a hurricane overnight, CNN meteorologist Tom Sater said.
"This storm is too powerful and its path is too uncertain to take any chances", South Carolina Governor Henry McMaster said in issuing his state's emergency declaration.
For many, the challenge could be finding a safe refuge: If Florence slows to a crawl just off the coast, it could carry torrential rains up into the Appalachian mountains, causing flash floods, mudslides and other unsafe weather across a wide area.
AccuWeather meteorologist Brett Rossi said the ground in North and SC and Virginia is already saturated from recent rains.
Two other storms were spinning in the Atlantic.
Walsh says we could see adjustments to the models throughout the next few days that may bring severe weather to SC including "tremendous amounts of rainfall" starting Friday along the coast.
"While it's still too early to know the storm's path, we know we have to be prepared", Gov. Cooper said.
Florence is moving toward the west near 9 km/h, and this general motion is expected to continue today. It was about 1,500 miles from the easternmost Caribbean islands on Sunday and could become a hurricane later in the day.