Some of the highest tides of the year are here, causing coastal flooding in South Carolina and likely closing some roads.
Although this round of high tides is not technically labeled as "King Tides" officially in South Carolina, as they occur in early October, the higher-than-normal tides are caused by the same astronomical event. Higher-than-normal tides occur due to the combined gravitational forces of the Sun and Moon, which pull on the Earth's oceans, creating the highest tides of the year. King Tides in South Carolina are predictable, happening 6 times this year: three in the Spring and three in the Fall.
Fun fact: King tides are particularly noticeable along the East Coast of the United States, but they are not particularly evident along the Gulf Coast due to the bathymetry or steepness of the sea floor, which has a shallow continental shelf. In the Lowcountry through the northern South Carolina coast, tidal waterways elevate and inundate nearby roads and streets, causing headaches for drivers.
Flooded roads, closures
The high tides have been increasing and are expected to reach a peak on Tuesday. On average, high tides will be approximately 1 foot higher than usual. In the Charleston area, the National Weather Service (NWS) Forecast Office in Charleston has established thresholds for flooding:
- Action Stage (6.5 ft. MLLW)
- Minor Flooding (7.0 ft. MLLW)
- Moderate Flooding (7.5 ft. MLLW)
- Major Flooding (8.0 ft. MLLW)
NOAA has also established a threshold for high tide flooding (HTF) in Charleston (7.6 ft. MLLW). Keep in mind that tide heights vary by location, and they can have slightly different times of occurrence.
Forecast: tidal flooding
For Tuesday at Charleston Harbor, the tide gauge is expected to reach 7.5 feet, resulting in moderate flooding.
Some roads were closed on Monday night due to coastal flooding. You can view the latest road closures, categorized by reason of closure, here. Expect more road closures as there will be more high tides inundating the roads. The next round is scheduled for Tuesday morning, and another one is likely to follow at night. This is saltwater inundation, which can damage vehicles. Please try to avoid it. Saltwater inundation will be possible 1 to 2 hours before and after high tide.
The first coastal flood advisory was issued and expired at Midnight on Tuesday. Another coastal advisory will be in effect from Tuesday morning to noon, with up to one foot of inundation above ground level expected along shorelines and tidal waterways (7.6 to 7.8 feet Mean Lower Low Water at Charleston).
Sea level rise is also contributing to higher-than-normal tides. The mean sea level is typically higher in the summer due to changing weather patterns and increasing water temperatures.
Across the northern coast of South Carolina, minor coastal flooding is expected along the lower Cape Fear River during each high tide as well as along the northeast South Carolina coast during each high tide between Monday evening and at least Wednesday morning.
The wind is coming mainly from the northeast, increasing the rip current risk along the entire South Carolina coast for much of this week. In areas where the wind becomes more straight from the east and increases on Wednesday, there could be more flooding, as more water may be pushed onshore by the wind. Please do not cross flooded roads, the salt water could damage vehicles and intrude into structures.
Luckily, rain showers will not contribute to the flooding, as the front remains well offshore, and dry weather is expected to continue through the rest of the week. The winds are expected to subside by the end of this week, and tides will gradually return to near-average levels.