At 8:14 a.m. on 4 May 2026, the tide gauge at the Customs House in Charleston, South Carolina, recorded a high water of 7.94 feet above the local mean lower low water datum. The street outside, at the corner of Concord and Cumberland, was under approximately ten centimetres of clear seawater.
The sky was cloudless. There had been no rain in Charleston for five days. The flood was, in the local parlance, sunny-day flooding.
Sunny-day floods, also called tidal floods or nuisance floods, are inundation events that occur entirely from astronomical tide, without storm surge or rainfall. They happen on the highest spring tides of the year, the so-called king tides, when the lunar and solar gravitational pulls align with the lunar perigee.
In 2000, Charleston recorded eleven sunny-day flood days. In 2010, twenty-three. In 2024, the count was sixty-seven. The 2026 NOAA projection for the city is between seventy-five and ninety days.
The increase is not because the tides themselves have grown larger. The lunar nodal cycle does add a small amplitude in the years near major standstill, but the bulk of the change is sea level rise. The mean sea level at the Charleston Customs House gauge has risen by approximately 28 centimetres since 1950.
Twenty-eight centimetres is enough. The street grid of the Charleston peninsula, much of it built on fill in the 18th and 19th centuries, sits low. Several blocks at the Battery, at the south tip of the peninsula, are at elevations of less than 1.5 metres above mean sea level. A king tide brings the harbour to within a few centimetres of the curb.
Mira Iyer, who edits Sea Marker's Lighthouses section and has studied coastal heritage in South Asia for fifteen years, visited Charleston in early May to write about Morris Island Lighthouse. She arrived during a king tide cycle and stayed an extra day to watch the flood.
At 7:30 on 4 May, an hour before high water, the East Bay Street drainage outlets were already audibly running in reverse. The city's stormwater system, gravity-fed to the harbour, has check valves at the outfalls. The check valves are meant to prevent salt water from flowing inland through the drains.
At king tides, the check valves fail to seat properly against the pressure. Water enters the drains from the harbour side and emerges, several minutes later, through manholes and gutters two and three blocks inland.
By 8:00, three intersections in the historic French Quarter were flooded. By 8:20, the count was eleven. The city's emergency operations centre had pre-positioned barricades at the worst spots overnight. A municipal pickup truck circulated the perimeter, repositioning cones.
The shopkeepers along East Bay had set out their flood boards. The boards are plywood panels, cut to the dimensions of each shop's threshold, reinforced with weatherstripping, and stored on a rack inside the front door from April through November. Most shops have used the same boards for a decade.
At Pearlz Oyster Bar on East Bay, the owner stood in the doorway at 8:15 with a coffee in one hand and a phone in the other. She had taken the photo, posted it to the shop's social media account with the caption Open as usual, dry inside, and gone back to setting up for lunch service.
"It is a Tuesday in May," she said. "It is the moon. We are open."
The city of Charleston has spent approximately 235 million dollars between 2015 and 2025 on tidal flood mitigation, including check-valve upgrades, drainage pump stations, and the elevation of several blocks of Calhoun Street. The Army Corps of Engineers has proposed a perimeter seawall project, the Charleston Peninsula Coastal Flood Risk Management Study, with a price tag exceeding two billion dollars.
The seawall is controversial. Critics, including several preservationist organisations, argue that an eight-foot harbour wall around the peninsula's historic edge would alter the city's character beyond repair. Proponents, including most of the city's working flood maps, argue that the alternative is incremental inundation of the historic district itself.
The decision has been deferred multiple times. The next scheduled federal review is in late 2027.
In the meantime, the tide rises and falls. The check valves are inspected twice a year. The shop owners along East Bay maintain their flood boards. The cars parked at the Battery on king tide days are mostly tourist rentals, whose drivers have not yet learned to read the local moon.
Sunny-day flooding ended at the Customs House gauge at 9:48 a.m. By eleven, the streets were dry. By noon the only sign of the morning was a faint salt residue on the brick at the corner of Concord and Cumberland, and the small white tide-mark that the city has stencilled on several lamp posts.
The stencil reads, simply, King Tide 2024. The 2026 stencil, when it is added, will sit a centimetre higher.
