Rain, Wind on the way to New England Before Halloween

New England's incoming storm has formed and is currently across the southeast. The system's primary low will take an interior track across the northeast. A secondary, coastal low still form on this system’s triple point (where a warm, cold and occluded front meet). This secondary low has trended weaker over the past few days, with the interior low remaining the primary low pressure system. This will result in a period of windswept rain across much of the region.

Initial showers from the system will likely move into western New England late Thursday afternoon and evening. These showers will fill in, become more widespread and steadily move northeast throughout Thursday evening. These initial showers will likely become steady to moderate rather quickly as the storm will be moving along at a pretty good pace, which will be the theme of this storm for its duration.

Below: FV3 showing potential weather late afternoon Thursday (1st image) and late evening Thursday (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. Given the track of the surface low, a dry slot may rather quickly punch into western New England Thursday night.

Below: FV3 showing potential weather Thursday night (1st image) and around mid-morning Friday (2nd image):

The system still looks to shut down by Halloween evening for a majority of New England. The storm system itself will likely be rapidly strengthening as it moves north and east, away from New England. Scattered showers may persist into the evening, especially across interior northern New England, but for the most part, Halloween evening and night look mainly dry and windy.

Below: Euro showing potential weather Halloween evening:

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. The secondary low will likely be strengthening as the system passes, so higher rainfall totals will be most likely across interior Maine as the system will have had the most time to strengthen by the time it reaches here.

Rainfall has trended a bit lower across the western half of New England as a dry slot looks to punch in rather quickly given the storm's track. The center of the primary low looks to pass over western New England, and dry slots are often seen around the center of these systems. You can see on the "timing" maps above that the system quickly reverts to scattered showers and downpours across western areas. With a gradually strengthening coastal low, eastern areas, particularly Maine, will see generally higher totals. The changes in the rainfall map below represent the overall uncertainty in the storm's exact track.

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.

At this point, only minor nuisance flooding is expected, with a "marginal" chance (level 1 of 4) of excessive rainfall now only covering extreme 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. The most recent trends have been for an earlier development of the secondary low, which has resulted in winds coming more out of the east-southeast rather than more southerly.

Below: GFS showing wind gusts and direction Thursday night:

As the steadiest of the rain exits throughout the day Friday, the main story with the system will shift to the persistent winds. As the system pushes through the northeast and into the Canadian Maritimes, it will become very deep. As it passes New England Thursday night to Friday evening, the system will likely drop from around 995mb to around 985mb. By Saturday morning, the system's central pressure may drop to around 975mb. This will support persistently high winds as the pressure gradient tightens. It will very gradually weaken through the weekend.