COLUMBIA — Gov. Henry McMaster urged all South Carolinians in evacuation zones to get out of Hurricane Florence's destructive path and doubled-down that those not ordered to go should consider fleeing if they're in a low-lying area.

"Go ahead and leave and go to find high ground because you may be in danger. This is a big, big storm," he said Wednesday. 

The flooding associated with Florence could be unprecedented, particularly in the Pee Dee region, where South Carolina rivers will converge and absorb the rainfall from North Carolina, said Alvin Taylor, director of the Department of Natural Resources. 

"This is bringing rain and water we haven’t seen before with hurricanes," McMaster said. "This will likely be more rain than with Hugo or other hurricanes." 

Hurricane Hugo, the last major hurricane to hit South Carolina in September 1989, came ashore just north of Charleston with winds of 135 mph. 

McMaster made the case for more people to leave a day after exempting the state's three southernmost counties — Beaufort, Jasper and most of Colleton — from Monday's evacuation order, which impacted the entire 187 mile coastline.

More than 760,000 people from Edisto Beach northward were still directed to leave, starting at noon Tuesday.

An estimated 300,000 people have already left, and those who refuse to leave the coast could be risking their lives, McMaster said. 

"There is some point no one can go out in a hurricane," he said. "You can call 911 or every other number, but just like you can’t get out, they can’t get in to save you."

Lane reversals on Interstate 26 and U.S. 501 remain in effect, in an effort to ease congestion for evacuees leaving the Charleston and Myrtle Beach areas. Those reversals will end Thursday at noon for U.S. 501 and sometime before 6 p.m. for I-26, so officers can get to safety as tropical-storm winds arrive.    

As of Wednesday afternoon, Hurricane Florence's winds were just shy of Category 4 strength but the storm is predicted to strengthen. It could be the most destructive storm to hit the Carolinas in decades. The latest forecast puts all of South Carolina in Florence's cone of uncertainty.

Florence could make landfall near Myrtle Beach on Saturday. Even if it hits land more northward, it's expected to veer into South Carolina and dump rain for days, causing flooding far inland, and could skirt the coast. Forecasts call for rain statewide, with up to 15 inches falling in the northeast corner from Horry to Marlboro counties. 

"This is expected to be a long-duration, high impact event, including areas well inland from the coast," said John Quagliariello, a National Weather Service meteorologist. 

Storm surges could reach up to 9 feet in North Myrtle Beach, he said. 

State-funded digital billboards telling people to "Leave Now" went up Wednesday in the evacuation zones. 

Historic flooding last occurred in 2015, when much-feared Hurricane Joaquin missed the East Coast but fueled what experts called a “fire hose” of tropical moisture that aimed directly at South Carolina. That dumped up to 2 feet of rain over several days and killed 19 people, most of them in the Columbia area.

Adjutant General Bob Livingston, leader of the state National Guard, stressed the need to pay attention and listen to storm updates. 

"This is not 2015. It is not Matthew (in 2016). It's Florence," he said. "Just because your home was not flooded last time, it may be flooded this time."  

Food banks across the state have been sending food to communities near the storm's predicted path for the past week. They're also partnering with agencies to supply emergency shelters before it hits, as well as help those in need once it passes.  

But "our shelves are bare," said Mary Louise Resch with Feeding the Carolinas, which has supplied $10.4 million worth of disaster relief in South Carolina since 2015. 

All three food bank branches along the coast are closed but warehouses in Columbia, Florence and Greenville are accepting donations through Thursday.

The biggest needs are bottled water and "anything in a pop-top can" in case of power outages, Resch said.   

Follow Seanna Adcox on Twitter at @seannaadcox_pc.

Assistant Columbia bureau chief

Adcox returned to The Post and Courier in October 2017 after 12 years covering the Statehouse for The Associated Press. She previously covered education for The P&C. She has also worked for The AP in Albany, N.Y., and for The Herald in Rock Hill.