Strong Coastal Storm

Another October…another big coastal storm.

Upper level energy diving southeastward across the Ohio Valley today will help initiate surface low pressure development along the Eastern Seaboard tomorrow. This surface low will rapidly deepen to the east of the Mid-Atlantic shores during the day on Tuesday and slow to a crawl Tuesday night and Wednesday, bringing a prolonged period of heavy rain and strong winds to the Mid-Atlantic and Southern New England. The storm will gradually wobble east-southeastward out into the western Atlantic Wednesday night and Thursday, with improving weather conditions during the day on Thursday.

The upcoming nor’easter will bring with it several weather hazards, including very heavy rainfall, possibly some thunderstorms, beach erosion and a lengthy period of powerful winds.

Rainfall: The combination of mid- and upper-level jet energy, a howling low level jet stream, anomalously moist air being wrapped north and westward from the subtropical Atlantic waters and the overall slow movement of the weather system will yield heavy rainfall across parts of the Mid-Atlantic and New England. There is still some discrepancy amongst the various computer models as to where the axis of heaviest rainfall will set-up but all guidance suggests widespread soaking rains of 1 to 3 inches across a large geographic area. The ribbon of heaviest precipitation could yield totals in excess of 5 inches, which will cause street/urban area type flooding, basement flooding, as well as some river flooding (interior).

Thunderstorms: While the storm system will eventually evolve into a traditional cold, nasty nor’easter, there is a window of time tonight when the atmosphere will be rather unstable and actually supportive of some thunderstorm activity around the region. Conditions are marginal but there is an outside shot that one or two of the cells that develop turn strong to severe during the nighttime hours tonight. In fact, the threat for a rotating storm with a waterspout or isolated tornado can’t be completely ignored (though conditions are not as “good” as we’ve seen in some of our recent events).

Beach Erosion: Thankfully, this system is hitting during a period of very low astronomical tides. The high tides overnight / very early Tuesday, Wednesday and Thursday mornings are only around 8 to 8.5′ and the afternoon / evening high tides are generally between 9 and 9.5′. Consequently, even a significant surge of 3 to 4 feet would only put water levels into minor to moderate flooding. That said, very large waves will pound the east and northeast facing shores for several days over successive high tide cycles resulting in substantial beach erosion and certainly some pockets of coastal flooding. Had this system hit 2 weeks ago…we’d have been dealing with a historic coastal event.

Damaging Winds: The wind threat is a bit of a wild card in the forecast. It is highly likely that the Cape will have a prolonged period of strong east and northeast winds starting Tuesday afternoon and continuing nearly unabated into Thursday morning. We can expect wind gusts over 40 mph throughout just about this entire period with peak gusts of 50 to 60 mph. With fully leafed trees and soaking rains, this will undoubtedly yield limb and tree damage and bring some power outages to the area. Given the slow movement of the storm, some of these outages could linger for a while. Prepare accordingly. HOWEVER – the story doesn’t quite end there. A couple of computer models want to spin a core of even stronger wind (70 to 80 mph gusts) onto the Cape Tuesday evening and Tuesday night, bringing a more substantial/threatening wind event to our area. If this idea gains traction during the day today (i.e. if additional guidance hones in on this threat), we’ll have to consider the possibility of a more serious, widespread damaging wind event for the Cape and Islands…with significant tree damage and lengthy power outages.

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