Coastal Storm to Bear Down on New England Beginning Sunday Afternoon

A coastal storm system will work up the east coast Saturday and Sunday. Its movement will likely be quick initially, but it will slow down as it reaches the Mid-Atlantic. The most likely timing for the system to reach toward New England will be later Sunday and Monday. This system will be the first fall nor'easter of the season and may bring heavy rain, winds and the potential for coastal flooding to at least a part of New England. There will likely be a large range in rainfall totals across New England, ranging from a few showers to a long-lasting, soaking rainfall.

After initially racing up the east coast, the storm will slow down and may even stall out for a while off the coast of the Mid-Atlantic. The center of the low pressure system will likely not rise much farther north than the Mid-Atlantic waters, though the precipitation shield will extend north of the center. The system will initially have to battle dry air over New England from high pressure to the north. Showers will likely work into southernmost New England Sunday afternoon and very gradually push northward through the evening and overnight hours.

Below: FV3 showing potential weather around mid-afternoon Sunday (1st image) and very early Monday morning:

The bulk of the rain and the wind will likely come during the day Monday, with a more widespread steady to heavy rainfall across southern and central New England getting going Monday morning. Showers will likely continue with varying intensity through much of the day Monday and into Monday night. Showers will likely begin to pull back from northern New England from north to south through Monday afternoon and evening.

Below: Potential weather Monday morning (1st image) and Monday afternoon (2nd image):

The high pressure around New England during this time is a rather strong one, and its position and exact strength will determine what kind of impacts New England sees from the nor'easter. Ensemble guidance over the past 24-48 hours have generally pointed toward a more southern solution for the system given the location and the strength of the high pressure just to the north of Maine. This keeps the heaviest rainfall and wind impacts across southern New England with a trend toward less rain across northern areas.

This overall setup is very much like a Rex-Block, where an area of high pressure sits directly north of an area of low pressure. The high pressure tries its best to block the low pressure from advancing northward. The fact that this is a blocking pattern adds inherent uncertainty to the forecast. A big question will be exactly how sharp the gradient is from the heavy rainfall across southeast New England and the lesser showers farther north and west.

Below: Weather map for Monday morning, showing a Rex-Block situation over New England:

At this point, there is much higher uncertainty regarding rainfall amounts north of a line from Rutland to Lake Winnipesaukee to Sebago Lake. South of this line could see a good 1 to 3 inches of rain, with the highest amounts across eastern Massachusetts. An inch or less of rain is possible north of the aforementioned line.

With trends toward a more southerly solution, it remains possible that the rainfall amounts below may need to be pushed farther south and east in future updates. The main question for northern New England (and far western portions of southern New England) will be just how tight the gradient will be between a few showers and a steady rainfall. Will the rain taper off gradually moving north and west or will it cut off abruptly?

Any rain this system produces is still much-needed. All of New England is now officially abnormally dry, with extreme drought conditions continuing to expand across northern New England. Unfortunately, the areas with the worst drought conditions are far less likely to see a good hit of rainfall with this system, but wherever the heaviest rain ends up will be welcomed. The only issue would be the potential for torrential downpours resulting in localized flash flooding, especially if it were to set up over an urban area.

Below: Current US drought monitor:

The other impact from this system could be the potential winds. A nor'easter off the coast and a rather strong area of high pressure to the north will lead to a tight pressure gradient. This will be supportive of strong wind gusts across the region. These winds would, naturally be strongest at the coast, but the tight gradient would support at least breezy conditions region-wide. Winds in excess of 40mph will be possible for coastal areas of southern and central New England. Gusts in excess of 50mph will be possible across Cape Cod and the Islands, where wind alerts are in effect.

A gusty northeast wind and rough seas will also promote the potential for some coastal flooding. At this time, the coastal flood threat does appear to be closer to the minor side. A coastal flood watch is currently in effect for the entire southern New England coastline. High tides will be around the early morning and early afternoon hours.