Flooding two hours before high tide in Old Town Alexandria on Saturday evening. (Melanie Mayhew)
By Jason Samenow
Jason Samenow
Editor and writer covering weather and climate

Since Friday, numerous locations along the tidal Potomac River and Chesapeake Bay have endured coastal flooding, due to the departure of Tropical Storm Melissa and the coming hunter’s full moon.

Water levels two to three feet above normal have washed over shorelines and adjacent roads in Old Town Alexandria, the District’s waterfront, Annapolis and Baltimore at around high tide.

For example, water lapped up over Ohio Drive in the District, flooded streets in Old Town and, according to the Baltimore Sun, covered the brick promenade at the Inner Harbor. In Annapolis, floodwaters disrupted the U.S. Sailboat Show, and some roads were closed.

And the flood threat isn’t yet over.

Coastal flood advisories and warnings first posted Friday remain in effect through Sunday. High water, about two feet above normal, is a particular concern at high tide. Here are upcoming high tides at select locations:

The high water along the tidal Potomac and Chesapeake Bay is partly in response to departing Tropical Storm Melissa. When Melissa meandered close to coastal New England on Wednesday and Thursday, winds from the north on its backside pushed water in the Potomac River and Chesapeake Bay south, away from Washington and Baltimore. But since the storm has retreated to the east and those winds have relaxed, the water (previously displaced) is sloshing back up the river and bay.

Making matters worse, the moon is nearing its full phase, which it reaches Sunday, elevating tidal levels. This month’s full moon, called the hunter’s moon, is officially full at 5:07 p.m. eastern Sunday.

But it’s not just the offshore storm and the moon contributing to these anomalous tides. The frequency of high-tide flooding in the Mid-Atlantic has increased dramatically in recent decades due to sea level rise.


Annual number of high-tide floods per year in Mid-Atlantic over time.

A 2018 report from the National Oceanic and Atmospheric Administration showed that in 15 years, the incidence of high-tide flooding in the Mid-Atlantic doubled from an average of three days per year in 2000 to six in 2015.

Given sea level rise projections, high-tide flooding could occur every other day by the end of the century, the NOAA report said.

Below are pictures of some of the flooding.

Photos

Potomac

Chesapeake Bay