"I think this is very Harvey-esque", said University of Miami hurricane expert Brian McNoldy.
Wind strength that high is catastrophic, with potential impacts including damage so severe that areas are left "uninhabitable for weeks or months", according to the hurricane center.
Cooper said 200 National Guard troops have already been activated.
Trump tweeted Monday afternoon that the federal government was monitoring the storm and was ready to help.
Officials in the Carolinas warned residents to prepare and to brace for impact. The evacuation zone includes the most flood-prone coastal areas, Northam said.
The South Carolina Emergency Management Division tweeted Sunday that officials there are "preparing for the possibility of a large-scale disaster".
Meanwhile, the Atlantic tropics were also flaring up beyond Florence.
The once powerful Florence took a hit Thursday, but its life as a major hurricane is likely not over just yet, and it has East Coast residents on the edge of their seats.
Florence, the most powerful storm to menace the US mainland this year, intensified into a Category 4 hurricane as it howled closer to the Carolinas on Monday, prompting evacuations of more than 1 million people to higher ground. The storm was centered about 765 miles southeast of Bermuda and moving west at 6 mph (9 kph).
The storm has sustained winds of 75 miles per hour. "That is a sign of a strengthening hurricane".
The Miami-based center said that it was still too early to predict the hurricane's exact path but that a huge coastal area from SC to the mid-Atlantic region should prepare for a major strike late in the week. The flooding might be similar to what the Carolinas experienced during Hurricane Matthew in 2016. Some areas further inland could also contend with damaging winds and flooding rain.
States in the U.S. have been braced for there impact of the storm for several days. Any Category 3, 4 or 5 hurricane is classified as a major hurricane. The European model has favored the Mid-Atlantic, but small changes in the storm's path could place the Southeast or Northeast coasts in the line of fire.
Forecasters said Monday the storm to come ashore by late Thursday or early Friday.
Odds have increased that this storm may have a hard time finding an escape route to the north as it draws closer to the East Coast, although a direct hit is not inevitable.
In 1989, Hurricane Hugo grew to a Category 4 storm before coming ashore near Charleston, South Carolina, where it caused about $14.1 billion in damage when adjusted for inflation, making it the 13th costliest US storm, according to Hurricane Center records. People in coastal communities are taking all precautions.
"While some weakening is expected on Thursday, Florence is expected to be an extremely unsafe major hurricane through landfall", forecasters said.
The hurricane's path was still far from certain Monday. Hurricane Floyd was a Category 4 storm before it hit Florida, traveled up the coast and struck Cape Fear as a strong Category 2 storm. "10.html">the school said in a statement posted online.
"Florence is expected to be an extremely unsafe major hurricane through Thursday", the NHC said in its latest bulletin.
Hours before Isaac became a hurricane, Helene strengthened into one. It was heading west at nine km/h. Since reliable record-keeping began more than 150 years ago, North Carolina has only been hit by one Category 4 hurricane: Hazel, with 130 miles per hour winds in 1954. Tropical storm force winds and some rain bands will likely begin Wednesday night, regardless of the actual landfall of the storm. Weakening is forecast to begin by the middle of the week.