It is estimated that the wind speed in the eye of the hurricane reaches 200 km/h.
About 10 million people could be affected by the storm. Significant weakening is expected over the weekend.
Satellites also continue to monitor Hurricane Florence as it passes over North Carolina to help meteorologists make more accurate predictions of how the storm will impact people living in the region.
Hurricane Florence is now a powerful Category 4 hurricane and is expected to make a unsafe impact once it makes landfall along the coast of the southeast USA later this week.
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Tropical Storm Isaac was east of the Lesser Antilles and expected to pass south of Puerto Rico, Hispaniola and Cuba, while Hurricane Helene was moving northward away from land.
As the trough moves east, it will disrupt the winds that steer the hurricane, Stewart said.
Hurricane Florence, a powerful Category 4 storm, could stall upon reaching the Carolina coast and make a slight shift south toward SC once it makes landfall, becoming "a major flooding event", according to Fox News Senior Meteorologist Janice Dean. Its trajectory showed its center most likely to strike the southern coast of North Carolina by late Thursday or early Friday, the National Hurricane Center said.
Both states, as well as Virginia, have ordered mass evacuations along the coast, as the NHC has warned that Florence will bring a "life-threatening storm surge", as well as catastrophic flash flooding and significant river flooding. Parts of North Carolina could get 40 inches (1 meter) of rain.