Coastal watches and warnings for rip currents and flooding dot the Eastern Seaboard from New York to Florida. This weekend’s supermoon coupled with a strong coastal low are to blame as waves and dangerous surf are set to ramp up through Sunday.

The majority of the action will be in the Carolinas and the Mid-Atlantic area. High tide will be up to 2 feet above normal for parts of the region. Add in waves forecast to reach 6-9 feet and you have a recipe for moderate coastal flooding and beach erosion in many places.

The rip tides will pose the most immediate danger and the National Weather Service has warned people to stay out of the water, particularly at low tide. Moderate coastal flooding will also be a major concern in cities like Norfolk, Va. and Charleston, S.C. while other parts of Virginia could see severe flooding.

“Two things do stand out about this event: the duration of onshore winds for North Carolina and Virginia and parts of the Mid-Atlantic along with the minimal surf that preceded this event,” Kurt Korte, lead forecaster at Surfline, said. “The Outer Banks of North Carolina have seen moderate to strong onshore winds since the 18th, so by the time this event is over, that’s about nine days.”

The Outer Banks has already seen serious beach erosion this week, a trend that will continue through the weekend.

Wind map shows Carolinas Storm
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A coastal low has sat parked offshore of the Mid-Atlantic for days and is forecast to come ashore in full on Saturday and Sunday. Meanwhile, high pressure is parked to its north. The difference in pressure between those two systems has helped drive strong winds and waves across the region all week, a trend that will continue and intensify this weekend as the low comes ashore. The supermoon is also giving tides a boost as well.

Korte said that this system might feel particularly large because it’s been such a quiet September so far. The Atlantic hurricane season has been quiet in large part due to the strong El Niño, which tends to create conditions that rip apart tropical systems.

 


Later this winter, El Niño could have the opposite impact. A report released earlier this month showed El Niño tends to change atmospheric circulation that tends to cause more winter storms to head toward the mid-Atlantic,
leading to more flooding.

The Carolinas and Mid-Atlantic are home to areas already prone to regular “sunny day” floods — floods that occur without any added push from storms — and the toll on those cities is rising due to sea level rise. Globally, oceans have risen about 8 inches since the start of the 20th century.

That seemingly small amount has already made coastal flooding 10 times more likely in Baltimore and five times more likely in Philadelphia, Norfolk, Va., and Charleston, S.C since 1930. By mid-century, continued sea level rise will mean those cities and others around the U.S. will reach a coastal flooding tipping point of at least 30 sunny day floods a year (and in many cases, a lot more).

The silver lining with this storm can be found inland, where much-needed rain in the Carolinas should help ease a severe drought that has developed over the summer. In South Carolina, the federal government recently declared 35 of the state’s 46 counties disaster areas, giving them access to federal funds. The rain from this system should offer a modicum of relief.