But forecasters warned that the widening storm - and its likelihood of lingering around the coast for days - will bring life-threatening storm surge and torrential rains.
North Carolina Governor Roy Cooper warned against complacency.
The National Hurricane Center said the storm's strength should continue through Thursday. Coastal storm surge is expected to be as high as 13 feet, according to the National Hurricane Center. Slower storms mean more rainfall over a smaller area. "This rainfall would produce catastrophic flash flooding and prolonged significant river flooding", the Hurricane Center said.
More than 1,200 USA airline flights scheduled for Thursday and Friday have been canceled, according to the flight-tracking service FlightAware.
The Hurricane Florence has began to unleash fierce rains across the U.S. southeast.
"It has moved in", said Jordan Baker, a meteorologist with the National Weather Service Office in Wilmington. "We're about to be in the thick of it".
More people were expected at arrive at more emergency shelters as the latest forecasts showed Hurricane Florence taking aim at the Carolinas Wednesday morning. And Florence is a large storm, with hurricane-force winds extending outward up to 80 miles from the center and tropical-storm-force winds outward up to 195 miles. And this, he said, is like nothing Toronto has ever seen. Areas further from the coast could see 6-12in of rain. "It will probably fall faster than it can leave. There will be some rain but at the moment it doesn't look as though that's going to be the issue". "While some weakening is expected to begin by late Thursday, Florence is still forecast to be an extremely unsafe major hurricane when it nears the USA coast on Friday", the NHC said in an 11 a.m.More news: Time almost up: Fierce Hurricane Florence aims at Southeast - Story | WFLD
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Forecasters said that Tropical Storm Isaac was now moving into the eastern Caribbean Sea and was located near 14.9N 61.8W or about 50 miles (75 km) southwest of Dominica at 11:00 a.m, with maximum sustained winds near 45 mph or 75 km/h.
Every now and then nature throws out a storm so massive we can only gaze upon it in humbling awe at its fearsome power. It's already been raining in these areas and the ground is sodden.
Just as Hurricane Florence closes in on the Southeast, the area covered by hurricane-force winds has doubled - meaning far more people will get blasted with winds 74 miles per hour or greater.
"Extremely unsafe winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage".
"People don't have to work the next day because of the hurricane".
The number of people told to evacuate in the Carolinas and Virginia has been estimated at more than 1 million, according to an NPR report. The storm's 12-mph forward speed Thursday morning was a marked drop from Wednesday's 17-mph speeds.
Having so many systems moving across the Atlantic at once also complicates forecasting because they influence one another, Blake said.