A predicted high tide came in substantially stronger than expected this morning across much of the southeast U.S., especially along the South Carolina and Georgia coasts. Near Savannah, the Fort Pulaski station reported a tide of 10.43 feet above mean lower low water (MLLW). Even including hurricanes, this is the third highest tide at Fort Pulaski since records began in 1935, beaten only by 10.47’ on August 11, 1940 and 10.87’ on October 15, 1947 (thank to Nick Wiltgen at The Weather Channel for these records). At Charleston, the high tide of 8.68’ this morning was the highest in 28 years, beaten by 8.84’ (January 1, 1987), 10.27’ (August 11, 1940), and 12.56’ during Hurricane Hugo (September 21, 1989). Motorists in the Charleston area were asked to avoid traveling onto the peninsula this morning, with many roads blocked by accidents and/or high water.

It doesn’t take a hurricane to produce historically high tides. In this case, the high water is the result of strong coastal flow from the northeast (which pushed water onshore due to the Ekman transport effect) combined with a perigean spring tide. The latter occurs when the moon at the closest point to Earth in its monthly orbit (perigean tide) and also happens to be either new or full (spring tide). Increasing sea levels as a result of human-produced climate change are making such events progressively worse. A NOAA primer on perigean spring tides notes: “In some instances, perigean spring tides have coincided with a shift in offshore ocean circulation patterns and large scale shifts in wind that have resulted in unexpected coastal flooding. It is expected that occurrences of minor ’nuisance flooding at the times of perigean spring tides will increase even more as sea level rises relative to the land.” In September, NOAA predicted that atmospheric patterns related to El Niño will tend to drive more water into the coastline this autumn and winter, possibly leading to record amounts of nuisance flooding, especially along the mid-Atlantic coast.

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Figure 5. Tidal records for October 24-27, 2015, at Fort Pulaski, Georgia, just southeast of Savannah. Image credit: NOAA Advanced Hydrologic Prediction Service.