The difference between the two groups, prior research has found, is often a difficult-to-forecast process in which the hurricane rapidly strengthens, usually in the presence of highly favourable environmental conditions, such as extra warm seas to considerable depths, lots of available humidity in the air and slack winds around the storm. "Don't bet your life on riding out a monster".
"Florence is going to drop tremendous amount of rain, not as much as [Hurricane] Harvey brought to Texas but there will nearly definitely be flooding", Salna says.
To hasten evacuations from coastal SC, officials reversed the flow of traffic on some highways so all major roads led away from shore.
Cooper, the governor of neighboring North Carolina, ordered an evacuation of the Outer Banks, barrier islands that are a popular tourist destination, and parts of coastal Dare County.
Last year's Hurricane Maria, for instance, spun up from a mere tropical depression into a Category 5 storm in just over two days; or 2015's Hurricane Patricia, whose winds in the Eastern Pacific exceeded 337kph, more than 80kph stronger than the weakest category 5 storms.
Florence could be only the second Category 4 storm to pummel the Carolinas since 1800, when record-keeping began.
OH will also feel the effects of Florence. All of those, however, made landfall south of where Florence is predicted to hit, and Florence's wind speeds are predicted to be higher than those four storms.
Steady streams of vehicles full of people and belongings flowed inland Tuesday as Gov. Roy Cooper tried to convince everyone on North Carolina's coast to flee.
The Federal Emergency Management Agency warned that storm surge watches and warnings are in effect for the entire North Carolina coast and parts of SC.
Craig Fugate, a former Fema director, said: "I'm afraid, based on my experience at Fema, that the public is probably not as prepared as everybody would like".
Utilities deployed crews and gear in advance, with workers en route to the region from at least 15 states, according to trade group, the Edison Electric Institute. Flash flooding and river flooding is also expected in these regions. One power station, Duke Energy Corp's Brunswick plant, the closest to the area where landfall is forecast, faced a likely shutdown as a precaution.
Airlines, including American and Southwest, have started letting passengers change travel plans that take them into the hurricane's possible path.
"Get to a safe place now or by Thursday morning", he said.
Parts of North Carolina could get 20 inches of rain, if not more, with as much as 10 inches elsewhere in the state and in Virginia, parts of Maryland and Washington, D.C.
We can't talk about the potential impacts of this storm without talking about how many people now call the area in Florence's path home. "We are totally prepared", Mr Trump said at the White House. Some 3000 people died in the aftermath of that storm.
Days before its arrival, Florence was already disrupting commercial operations.
Schools in southeastern North Carolina were closed on Tuesday and will not reopen until Monday.
He did confirm models were picking up on some wind shear - when wind blows in the opposite direction and disrupts a system - entering the equation around the time of expected landfall late Thursday into Friday.