Storm Set to Bring Rain, Some Wind to New England Before Halloween

Today will be the driest day with the most sun for most of New England (the exception will be coastal areas of southern New England). A storm system will pass well south of New England later Tuesday into Wednesday. The rather strong high pressure to the north of New England and the overall weak nature of this storm will keep it well offshore of the region.

Despite its offshore track, low-level northeast flow will likely lead to a cloud cover developing over eastern areas of New England for tonight into Wednesday. Occasional ocean-enhanced showers will likely grace eastern Massachusetts, particularly the South Shore and Cape Cod tonight into Wednesday as well.

Below: HRRR showing potential weather early Wednesday afternoon:

This system will form in the deep southeast before pushing up the eastern United States and into New England. Confidence has increased that the track of this storm will be more of an “inside runner” with the primary low pressure system passing just west of New England. A secondary, coastal low may still form on this system’s triple point (where a warm, cold and occluded front meet). This secondary low has continued to trend weaker, with the system's primary low moving to the west and eventually north of New England. This will result in a period of windswept rain across much of the region.

The timing of this system has been a thorn in forecasters sides for the better part of a week now. With that said, some semblance of when this storm will play out is starting to come together. Showers will likely move into western New England Thursday afternoon. These showers will fill in, become more widespread and steadily move northeast throughout Thursday evening.

Below: Euro showing potential weather Thursday late afternoon (1st image) and Thursday evening (2nd image):

The main band of heavier rainfall is expected to move from southwest to northeast across New England Thursday night until it exits eastern Maine by midday Friday. Some lighter rain will persist after the main band of rain and wind passes. This rain will become more by way of scattered showers throughout the day Friday. Showers will become more and more isolated from southwest to northeast Friday afternoon and evening.

Below: Euro showing potential weather Thursday night (1st image) and around mid-morning Friday (2nd image):

The height of this storm may be rather brief, with several hours of a moderate to heavy windswept rainfall within a band. This band of heavier rainfall and stronger wind looks to move from southwest to northeast across New England later Thursday through Friday morning. Just how much rain falls in this band will likely be dictated by how much interaction occurs with Hurricane Melissa. Melissa will pass well offshore of the eastern United States late this week, but a plume of tropical moisture will likely get injected into our non-tropical storm, which would help enhance rainfall.

As stated below, recent trends have continued to point toward a stronger primary low moving well inland rather than a coastal storm strengthening and taking over off the coast of Cape Cod. This supports a strong low-level jet and high moisture advection from the south. A widespread 1-3 inches of rain is likely, with most falling within a six hour window. The most aggressive guidance paints a picture of 2-4 inches, with some 4+ inch totals. For this to occur, a stronger secondary low would need to form, and guidance has been steadily trending away from this happening.

At this point, only minor nuisance flooding is expected, with a "marginal" chance (level 1 of 4) of excessive rainfall now only covering southwest Connecticut (this area covered most of New England a couple days ago). For more impactful flooding to occur, including river flooding, over four inches would likely be needed over the headwaters due to ongoing drought conditions and low stream flows. This rain will likely be more beneficial than anything, especially for northern New England.

The pressure gradient between the high pressure to the north and the strengthening low pressure passing near New England will support a period of strong winds as well. This pressure gradient does not look like it will support truly significant wind, but gusts of 30-50mph will be possible across the coastal plain. Winds will be less farther inland. With a stronger primary low, winds will be out of the south-southeast (no more nor'easter with this one).

Again, Friday will likely see the height of the storm push out of most of New England through the day Friday. Scattered showers from the remaining instability will likely hang around for a while, but Friday evening looks mainly dry for most at this time. It will also likely remain breezy well after the storm passes due to the continued tight pressure gradient, so Friday evening will likely still be seeing gusts of 20-30mph.