The Saffir-Simpson scale that meteorologists use to measure hurricanes reflects only the wind speeds involved in the storm, and right now Hurricane Florence's winds are hovering at maximum speeds of about 110 miles per hour (175 km/h).
People in areas vulnerable to the risky hurricane, particularly those in coastal regions, have fled ahead of the storm.
The hurricane, whose wind field size is now larger than North Carolina and SC combined, is expected to make landfall on the Carolinas early Friday.
Two other tropical storms - Isaac and Olivia - have also been in the vicinity this week, with the National Weather Service estimating that some 10.15 million people lived in areas under either hurricane or tropical storm warnings.
"Don't play games with it".
Having so many systems moving across the Atlantic at once also complicates forecasting because they influence one another, Blake said.
The storm's centre was about 100 miles (160 km) southeast of Wilmington, North Carolina, at 3 p.m. EDT (1900 GMT) but already some 19,000 homes and businesses in the Carolinas and Virginia were without power by mid-afternoon. In some counties, almost 1 in 3 people live below the poverty line.
Home Depot and Lowe's, the two USA major hardware chains, said they sent around 1,000 trucks of generators, trash bags and bottled water and other items to their stores in the region as emergency response, according to local media reports. The two hardware chains said they sent in a total of around 1,100 trucks.
Antonio Ramirez, a construction worker from El Salvador living in Leland, North Carolina, said he planned to ride out the storm with his dog Canelo.
The US National Hurricane Center warned that "life-threatening, catastrophic flash flooding and prolonged significant river flooding are likely over portions of the Carolinas and the southern and central Appalachians". Harvey was an excellent example of how the rain from a hurricane can be its own tremendous danger, and there's no point in taking chances.
Computer models of exactly what the storm might do varied, adding to the uncertainty.
Hurricane Florence has come closer to the US East Coast as disaster mobilisations expanded south from the Carolinas into Georgia to counter the threat of deadly high seas and calamitous floods. In Virginia, 245,000 coastal residents were ordered to evacuate. By Sunday, Florence will have dissipated to a tropical storm, and by Monday morning it will be a tropical depression.
The shift in the projected track spread concern to areas that once thought they were relatively safe. "We just want prayers from everyone".
"We've had our lessons".
Tropical storm force winds are thought to be just hours away from making landfall in North Carolina. Unsure of what they might find when they return home, the couple went shopping for a recreational vehicle.
All four major USA airlines have said they are capping selected airfares below what last-minute tickets would cost. "We're going to stay tight and check on everybody", he said. As of now, Florence is due to make landfall very early Friday morning, somewhere in the Carolinas.
Myrtle Beach International Airport in SC has also suspended commercial operations, and urges passengers to check with their airlines - not the airport - about upcoming itineraries. As it sits over a particular area longer, there is more rainfall.
"It's been really nice", Nicole Roland said.