South Carolina and Georgia’s coastlines could be significantly impacted by storm system Ian, according to a new US Geological Survey coastal change forecast released on Thursday. 

At 5 p.m. on Thursday, the National Hurricane Center forecast that newly strengthened Hurricane Ian would hit the South Carolina coast as a Category 1 storm on Friday. Storm surge is anticipated to reach between 4 to 7 feet in South Carolina from Edisto Beach to Murrells Inlet, including Charleston, it said.

USGS researchers are forecasting the waves and surges caused by Ian may cause 11% of South Carolina’s and 1% of Georgia’s dunes along sandy beaches to be inundated — meaning continuously covered by ocean water. 

“This is the most severe type of storm effect on coastal beaches, with flooding behind the dunes that may impact coastal communities,” the USGS said. 

In addition, approximately 43% of South Carolina’s and 24% of Georgia’s dunes along sandy beaches are expected to be overwashed by Ian. Overwash is considered the second most severe level of coastal damage, taking place when water levels reach higher than the top of dunes.

“When a beach is overwashed, sand can be pushed and deposited inland, causing significant changes to coastal landscapes and blocking roadways,” the USGS said. “Overwash can reduce the height of protective sand dunes, alter beach profiles and leave areas behind the dunes more vulnerable to future storms.” 

In South Carolina 99% of the dunes and in Georgia 77% of dunes are projected to face some level of erosion caused by Ian, the USGS said. Erosion at the base of sand dunes is considered the least severe level of storm damage on sandy shorelines.