A developing storm system will combine with high astronomical tides to bring areas of serious coastal flooding to the shoreline of Georgia, eastern Florida and South Carolina late Friday and into the weekend. Persistent onshore flow brought by gusty easterly winds will pile water up against the coastline, threatening vulnerable property and causing widespread splashover.
Coastal flood watches stretch from the Treasure Coast north into southeast Georgia, and advisories, watches and warnings will “definitely” be expanded northward into South Carolina, according to the National Weather Service.
Due to the astronomical high tides, some minor coastal flooding has already been observed around Charleston, well ahead of the storm.
When the storm makes it closest approach, the National Weather Service in Jacksonville, Fla., is calling for water levels 2.5 to 3.5 feet above normally dry ground at high tide Saturday morning.
“Numerous roads may be closed,” it wrote, noting that “homes, businesses and some critical infrastructure may be inundated.” There’s also a high rip current risk.
It comes barely a week after an inauspiciously placed storm over the Appalachians spurred near-record coastal flooding in parts of the Mid-Atlantic. In Annapolis and Alexandria, Va., waters rose to their highest level since 2003.
Triple trouble for tidal concerns
Now a new storm is materializing in the Gulf of Mexico and will intensify east of the Florida Peninsula as it drifts north Friday evening. Low-pressure systems in the Northern Hemisphere spin counterclockwise, meaning an influx of warm, moist air will buffet the coast north of the low’s center. That channel of onshore winds will induce coastal flooding.
The timing is less than ideal, since we’re approaching the peak of November “king tides,” which will be most elevated through Tuesday.
A king tide describes a tide made even more extreme thanks to the positions of the sun and moon, combined with the interactions of various weather systems. Earth is nearing perihelion, or its closest pass by the sun, while the moon is also approaching perigee, meaning it’s nearest to us in its 27.3 day orbit. The result is more gravitational tug on the waters, resulting in higher tides.
The location of high pressure also helps amplify easterly winds, which boosts tides even more. September, October and November often feature action-tier flooding in vulnerable places such as Miami and Charleston, S.C., on otherwise fair weather days with blue skies. Climate change and sea level rise are making that flooding more frequent and severe. Miami, for instance, has seen a 12-fold increase in action-tier flooding since only the mid-1990s.
Add a coastal storm into the mix, and it comes as no surprise that flooding is expected.
What to expect
Low pressure will form along a cold front in the eastern Gulf of Mexico west of the Florida Straits on Friday. It will pass over central Florida on Friday night with showers and a few thunderstorms before emerging north of the Bahamas overnight into Saturday morning.
The low will intensify during the day Saturday, drawing in more air. In the process, surface winds will strengthen. The unusual setup will yield a corridor of 30 to 40 mph easterly or northeasterly wind gusts from roughly Jacksonville to the Outer Banks, N.C. A few gusts approaching 50 mph can’t be ruled out.
That will help amplify tidal flooding and bring a storm surge of several feet that could inundate low-lying areas near the coast.
Fort Pulaski, east of Savannah, Ga., is forecast to see peak water levels reach major flood stage Saturday. The predicted level would be fourth highest on record and comparable to an October 1947 Category 2 hurricane, according to Weather.com.
Moderate to major coastal flooding is anticipated around Charleston between Friday and Sunday, with Saturday’s peak water level potentially ranking in the top 10 highest on record. About two feet of inundation is possible.
Weather models also depict showers and downpours, relegated mainly to the immediate coastline.
“If showers occur around/at the time of high tide, any future or ongoing flooding could be exacerbated,” wrote the National Weather Service in Charleston, S.C. Inland rainfall would drain toward the coast, funneling into rivers that will already be backed up. Most of the rain should stay off the coast, with the exception of in north Florida, where three to five inches is possible.
By the latter half of Saturday, the storm should be heading past the Outer Banks, where minor coastal flood is anticipated, as it makes a run out to sea. Tides may remain elevated and seas choppy through the weekend, however. Waves just offshore may build to 20 to 30 feet tall.
Jason Samenow contributed to this report.