693
FXUS61 KBOX 201953
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
353 PM EDT Sun Sep 20 2026

.WHAT HAS CHANGED...
Gale Watch has been issued for portions of the southern ocean
waters Tuesday afternoon into Thursday.

&&

.KEY MESSAGES...

- Light rain continues this afternoon into early Monday morning.
  Breezy, cloudy, and cooler Monday afternoon.

- Dry and cool through mid week. Watching the potential for a
  coastal low to form mid to late week, bringing chances for
  strong winds and rainfall heading into the weekend.

&&

.DISCUSSION...
KEY MESSAGE 1...Light rain continues this afternoon into early
Monday morning. Breezy, cloudy, and cooler Monday afternoon.

A raw, cool, and rainy afternoon continues across southern New
England, with rain persisting through much of the evening.
Rainfall will be predominantly stratiform with generally light
to occasionally moderate rainfall rates. A rumble of thunder
cannot be ruled out near the south coast, though the risk is
quite low. Overall, additional rainfall amounts of 0.25-0.75
inch are expected, with some localized variability. Flooding is
not a concern with this event. Rain gradually shifts offshore
overnight, coming to an end by or before daybreak Monday. It
remains raw and wet overnight, with lows in the upper 40s to
lower 50s and a breezy northerly wind.

As for Monday, showers linger just offshore along a frontal
boundary while 1030 mb high pressure builds in from the
northwest. This results in a tightening pressure gradient and
breezy north-northeast winds throughout the day, especially near
the coast where gusts top out around 20-25 mph. Clouds hang
tough for much of the day, though there may be a few glimmers of
sunshine. It will remain cool, with highs ranging through the
60s. Clouds remain Monday night as well, with lows falling into
the 40s across much of the region, while the urban centers
remain in the lower 50s.

KEY MESSAGE 2...Dry and cool through mid week. Watching the
potential for a coastal low to form mid to late week, bringing
chances for strong winds and rainfall heading into the weekend.

Ensemble guidance remains in good agreement that an anomolously
strong high pressure system will develop over Quebec Tuesday
and linger into Wed/Thurs. This system likely keeps temperatures
across New England cooler than normal, in the low to mid 60s,
with a cooler airmass and several days of prolonged
northeasterly flow. Despite the large areal coverage the
Canadian high spans, guidance indicates the formation of a weak
Tuesday across the Mid-Atlantic region that could push just far
enough north into NJ to brush southern New England with spotty
showers. Still some uncertainty in how far north that low could
move, but general consensus in some low-end PoPs across the
southern coast Tuesday... higher chances across southern CT,
closer to NYC.

Both deterministic and ensemble guidance continue to indicate
potential for a coastal low to form Wednesday into the later
half of the week. While there is still a large amount of
uncertainty in the forecast this time, the overarching trend has
been the low slowly meanders north into the waters south of
Nantucket; however, each model has this low taking a slightly
different track: the GFS pushing further NE and closer to
Nantucket, and the ECMWF further NW and closer to Long Island.
Regardless, this system is likely to bring strong winds, rain,
and the potential for erosion/coastal flooding.

Highest confidence at this time pertains to winds, especially
over the waters. As the low deepens and approaches to the south,
the Canadian high over Quebec is also likely to strengthen and
expand, leading to a tighter pressure gradient over New England.
Given there`s still uncertainty in how strong the low and high
get as well as the track of the low, there is still some
question as to how strong the gradient will get. However,
confidence is increasing in the potential for Gale Force winds
across the southern waters, and a Gale Watch has been issued for
Tuesday evening through at least Thursday morning. The latest
ensemble guidance is also showing roughly 50 percent
probabilities of Storm Force wind gusts across the ocean waters
south of Long Island and Block Island as well as 20 to 30
percent probabilities of Storm Force gusts over Nantucket Sound
and Cape Cod Bay as the low deepens Friday into Saturday. Winds
over land along the south coast, Cape, and Islands throughout
the week are more likely to be a touch slower than the marine
winds, but still gusty... more on the order of 25-35 mph.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

18Z TAF Update:

Through Tonight...High confidence in trends, moderate
confidence in timing and ceilings.

MVFR to IFR with areas of -RA. The threat for LLWS has
lessened, though it cannot be ruled out as a weaker low-level
jet shifts across southern New England between 18z-06z.
Otherwise, winds generally SE to ESE at 5-10 kt. Chances for
embedded thunderstorms are very low to near zero. IFR ceilings
become more widespread overnight, with localized LIFR possible.
Visibilities generally 2- 5SM with -RA continuing overnight. -RA
ends from west to east mainly between 06z-12z as winds shift to
the N at 8-12 kt.

Monday...High confidence in trends, moderate confidence in
timing and ceilings.

IFR/MVFR improving to VFR through the day, though exact timing
remains somewhat uncertain. NNE to NE winds increase to 10-20
kt, with gusts up to 25 kt possible across the Cape and Islands,
where sustained winds will also be strongest. Winds diminish
somewhat heading into Monday night.

Monday Night...Moderate confidence.

VFR, though lower-end VFR ceilings are possible near the
southern coast and Islands, potentially impacting terminals such
as KACK. NNE winds 8-12 kt, increasing to 10-15 kt across the
Cape and Islands.

KBOS Terminal...Moderate confidence in TAF.

Timing of IFR onset remains somewhat uncertain, but is
generally expected after 21z. Have hinted at this potential with
SCT groups at IFR levels for the time being, at least through
05z. IFR overnight, with ceilings improving between 10z-14z. NNE
gusts up to 25 kt possible Monday afternoon.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night: VFR. Windy with gusts up to 30 kt.

Wednesday: Mainly VFR, with local MVFR possible. Windy with
gusts up to 30 kt.

Wednesday Night through Thursday: VFR. Strong winds with local
gusts up to 40 kt.

Thursday Night: VFR. Strong winds with local gusts up to 40 kt.
Slight chance SHRA.

Friday: Mainly VFR, with local MVFR possible. Strong winds with
areas of gusts up to 45 kt. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Through Monday Night...High Confidence.

A low pressure system riding along a frontal boundary brings
widespread rain to the waters this afternoon and evening. There
is a low chance for a few rumbles of thunder, primarily across
the southern waters. Rain ends early Monday morning, though a
few showers could linger across the southern outer waters as the
front sags south. Winds shift from E/SE to N/NE tonight as the
front pushes south. Gusts increase with cold air advection
Monday morning, which has prompted Small Craft headlines for all
southern waters and Cape Cod Bay through Monday afternoon. Seas
build to 3-5 ft, with the highest seas across the outer waters.
Winds subside Monday evening, albeit briefly, ahead of another
period of stronger winds Tuesday, for which a Gale Watch has
been issued.

Outlook /Tuesday through Friday/...

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain
showers.

Tuesday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 12 ft. Slight chance of rain showers.

Wednesday: Strong winds with gusts up to 35 kt. Rough seas up
to 15 ft.

Wednesday Night through Thursday: Strong winds with gusts up to
40 kt. Rough seas up to 16 ft. Slight chance of rain showers.

Thursday Night: Moderate risk for gale force winds with gusts
up to 45 kt. Rough seas up to 16 ft. Chance of rain showers.

Friday: gale force winds with local gusts up to 45 kt. Rough
seas up to 16 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Monday for
     ANZ231>235-237.
     Small Craft Advisory from 8 AM Monday to 3 AM EDT Tuesday for
     ANZ254>256.
     Gale Watch from Tuesday afternoon through Thursday afternoon
     for ANZ255-256-282-283.

&&

$$

DISCUSSION...Dooley/McMinn
AVIATION...Dooley/McMinn
MARINE...Dooley/McMinn