National Weather Service United States Department of Commerce

Overview

After a hot September with generally benign marine conditions, a fall cold front crossed the local area on Monday, September 21. The CAA behind the initial FROPA was not particularly strong. However, northeast winds began to ramp up during the night of 9/22 and especially later on 9/23 as anomalously strong (~1040mb) high pressure built into eastern Canada and weak low pressure began to strengthen off the Carolina coast. Frequent gusts of 35-40 knots were observed over the marine area on 9/23 with northeasterly gale force gusts continuing on 9/24 as the synoptic pattern remained similar. This prolonged period of strong northeasterly gusts allowed for seas to build to an impressive 10-17 feet nearshore by Thursday, 9/24. As a result of the high winds and seas, water levels rose to 2.5-3.5 feet above astronomical tides by Wednesday and Thursday, with the highest anomalies initially being observed across the SE VA/NE NC coast, lower and middle Chesapeake Bay, and tidal James River. 

Water levels fell a little bit on Friday as the wind direction turned to the north. However, on Friday night into Saturday, the low offshore rapidly deepened off the VA/MD coast and became a Nor'Easter as it slowly tracked to the north with significant impacts felt all along the Mid-Atlantic/Northeast coast. The tightening pressure gradient on the back side of the Nor'Easter allowed for storm force north-northwesterly gusts across the coastal waters north of Chincoteague and seas likely around 20 feet (occasional waves could have easily been 30 feet based off the usual wave height distribution) off of Ocean City, MD. These building seas allowed for water levels to rise area-wide despite the wind direction becoming more out of the north-northwest. Peak water levels in many places occurred during the Saturday morning high tide. Actually, at Ocean City, the north northwest wind helped to push the water that had already built up in the bays right toward the inlet. As a result, water levels finally rose above 5 feet MLLW for the first time in nearly 14 years! Perhaps the most significant part of this event was the duration of moderate to major tidal flooding, with several locations seeing 8-10 straight tide cycles of moderate to major flooding. 

By far, tidal flooding was the main story here with wind impacts over land remaining localized to the coast (and not anything out of the ordinary). Widespread heavy rain was not observed with this event, but localized flooding occurred during the day on 9/22 into the early morning on 9/23 in a few areas.  

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