Between 1953 and 2000, Charleston experienced minor flooding an average of eight times per year, according to the National Weather Service. In the past decade, that number has quintupled to more than 41 instances annually.
Monday’s event was classified as major flooding, a threshold reached only six times between 1953 and 2000, yet has happened eight times in the past two years, according to the weather agency.
“On the satellite, you could see the tide come in,” said Neil Dixon, an NWS meteorologist at in Charleston. It’s the first time he’s witnessed such a thing.
“It was really striking to see some of the marshy areas fill in with water,” he noted. “We did reach coastal flood criteria a few minutes [after noon]. A lot of water pushed in.”
About a foot of water flooded the Battery in southern Charleston, also inundating parts of Murray Boulevard.
Pockets of flooding were also concentrated in Westside and Harleston Village, including north of the medical district and along the Ashley River.
Flooding wasn’t limited to the city. Many beaches suffered erosion and rip currents, with water levels running a little over two feet above normal.
September through November marks a key overlap of factors — including Earth’s proximity to the sun and the position of key weather systems — that now make nuisance flooding routine. The fall location of a zone of high pressure near Bermuda, around which air flows clockwise, helps augment onshore winds, while tides are often more dramatic in the fall anyway.
The current flooding is the result of a trifecta of influences.
“The primary drivers of the tide are the astronomical forces,” Dixon said. “We just had a new moon and a perigee where the moon’s passing close to the Earth, so these are going to be pretty elevated [tides] anyway.”
Offshore high pressure is also instrumental.
“Then we have this area of ridging, of surface high pressure that provided these gusty northeasterly winds,” Dixon explained. “That’s a known wind direction for high tides. It’s been pretty persistent northeasterly for several days, building water up along our coast.”
Antecedent weather from tropical systems played a role, too, as did a pair of tropical systems. Hurricane Sally’s remnants brought heavy rainfall to the Carolina Piedmont and Virginia Tidewater, much of which entered river basins and flowed to the sea.
“We do have some fresh water that’s being routed out [to sea],” said Dixon. “That’s from Sally. That [storm] moved across the western Carolinas and dumped a lot of rain. That’s kind of in the drainage area in northern Georgia and western South Carolina. That water is being routed down the rivers, so we’re seeing a bit of a freshwater influence as well.”
Hurricane Teddy, meanwhile, spent the first part of the week cruising north of Bermuda as it underwent extratropical transition and targeted the Canadian Maritimes. Fifty-foot waves are likely over the waters south of Nova Scotia. Those stirred-up seas have exacerbated splash-over concerns and made the Carolinas’ coastal flooding even worse.
“Some waves sourced from Teddy at high tide have been running up the beach and over the dunes,” Dixon said.
But the biggest contributor to recent coastal flooding has been sea level rise, leading to regular inundation of coastal areas. Since 1950, Charleston’s average water level has risen about 11 inches. That has skewed the odds of flooding toward being disproportionately more likely, especially for higher-end events.
It’s like being a young child and struggling to reach the kitchen countertop. Even if they jump, they may not make it. But over time, the child gets taller, and suddenly reaching the countertop isn’t that impressive a feat. Eventually, it becomes routine — much like the Southeast’s King Tide flooding.
In Charleston, major flooding has been 18 times more common since 2015 than before, and that number will only grow as the seas continue to swell.
“Since the ’90s onward, there’s been a pretty noticeable increasing trend in these events,” Dixon said. “Sea level rise, some development issues, and more and more development closer to the water” are all playing a role, he said.
More flooding is likely, and it’s not just Charleston reeling from it. Miami has seen a 12-fold increase in “action”-tier flooding since 1996, with entire neighborhoods regularly inundated on sunny days without stormy weather. This most recent King Tide event has produced sunny-day flooding from South Florida to New England.
While such sunny-day flooding is a nuisance, as sea levels continue to rise and hurricanes become stronger, the risk of a devastating storm surge that brings even more serious inundation along the East Coast multiplies.