Storm surges could reach six to nine feet from south of Savannah, Georgia, up through Edisto Beach, South Carolina, according to the National Hurricane Center.
Charleston had tides as high as 9.29 feet early Saturday, about five feet above normal.
On top of concerns about flooding and storm surges, "powerful Category 2 winds in a saturated ground like this can easily topple trees and electricity poles," said CNN weather anchor Derek Van Dam.
The storm could dump about eight to 12 inches of rain in the Carolinas, exacerbating the potential for floods.
CNN`s meteorologists projected that the hurricane could make landfall as early as Saturday morning.
Matthew was blamed for the deaths of four people in Florida.
The dead included a woman in her 60s in Volusia County who was killed by a falling tree and an 82-year-old man and a woman in St. Lucie County, officials said. The latter two had medical emergencies and responders were unable to reach them in time because of hazardous weather.
A woman in northeast Florida died after a tree fell on her camper trailer, the Putnam County Sheriff`s Office said.
Matthew left more than 1 million people without power as it spent the day plowing north just off Florida`s east coast. Water from the storm rushed through streets, making roadways look more like rivers, in parts of Jacksonville, Merritt Island, Fleming Island and other Florida communities.
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