Forecasters say those areas could be battered with hurricane conditions for at least 24 hours.
Florence's expanse has even captured the attention of the astronauts and cosmonauts aboard the International Space Station, who have been tweeting pictures of the storm back to Earth.
The incredible video, recorded on Monday, shows the Lockheed WP-3D Orion flying through the strong winds of the hurricane until it reaches the eerily calm eye.
Chris Landsea, chief of the analysis and forecast branch, told the Associated Press that such waves are entirely possible within the storm, but there's also a chance "radar misinterpreted rain as an 83-foot wave".
Hurricane Florence is now expected to hit the Carolina coast with less powerful winds, a trade-off with increased rainfall - which may ultimately be more damaging for some areas.
The first tropical storm-force winds of at least 39 miles per hour (63 kph) were forecast to hit the coast on Thursday.
Everyone in the Carolinas should continue to finalize their preparations for the storm Wednesday.
Hurricane and storm surge warnings are in place from South Santee River, South Carolina, to Duck, North Carolina.
Duke Energy warned that Florence could cut off power to anywhere from 1 million to 3 million customers in North and SC, potentially leaving them without electricity for several weeks, said spokeswoman Grace Rountree.
More than 1 million have been ordered to evacuate the coastlines of the Carolinas and Virginia. The Appalachians could see 3 to 6 inches of rain, with isolated areas of 12 inches.
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"We can not stress this enough, Florence poses a very serious threat to people who live far away from the coast", said a National Weather Service tweet late Tuesday.
The result: Catastrophic inland flooding that could swamp homes, businesses, farm fields and industrial sites.
The hurricane center also adjusted its projected track but stayed north of what most computer models were showing to prove some continuity with past forecasts.
That is causing the so called "cone of uncertainty" to expand. Residents in coastal areas should follow evacuation orders from local officials because of the potential for life-threatening storm surge flooding.
Tropical storm force winds are in the 39-73 miles per hour range, says NOAA.
By late Thursday into Friday, steering patterns in the atmosphere may completely break down causing the storm to stall just off the coast of southeast North Carolina and northeast SC.
Florence is being trailed in the Atlantic by two other storms - Hurricane Helene and Tropical Storm Isaac.
"Florence is forecast to be an extremely unsafe major hurricane as it approaches the USA coast", the NHC said. "The storm is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up [to] 8 inches across Martinique, Dominica and Guadeloupe", the U.S. National Hurricane Center advised Wednesday.
Hurricane Florence has been downgraded to a Category 2 storm but it is still considered an extremely risky and life-threatening storm.
Florence is now churning through the Atlantic, only a few hundred miles off the coast of Wilmington, N.C.