417
FXUS61 KBOX 210609
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
209 AM EDT Mon Sep 21 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 /06Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

06Z TAF Update:

Through 12Z...High confidence in trends, moderate confidence in ceilings.

IFR with localize LIFR ceilings early this morning with visibilities
generally mainly between 2-5SM. Patchy fog possible through 12Z.
-SHRA slowly exits the eastern terminals early this morning and
 should be offshore the Cape and Islands by 15Z. Winds shift to
 the N at 8-12 kt.

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

IFR/MVFR improving to VFR through the day, though exact timing
is lower confidence. General trend is ceilings improving to VFR
09-14Z for interior terminals and 13-16Z for more east terminals
(BOS, PVD). Improvement trend will be likely slow for
Cape/Islands potentially not VFR until 18Z-21Z. NNE to NE winds
increase to 10-15 kt, with gusts up to 25 kt possible across
the Cape/Islands. Gusts diminish by 00Z, although sustained
winds 10-12 kts possible for Cape/Islands early evening.

Tonight...Moderate confidence.

VFR. Lower-end VFR ceilings are possible near the southern
coast and Islands closer to 12Z. NNE winds 8-12 kt, increasing
to 10-15 kt across the Cape and Islands.

KBOS Terminal...Moderate confidence in TAF.

Ceilings improving to VFR 12-15Z. NNE winds 8-12 kts with gusts
up to 20 kts developing after 15Z through around 21Z.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy.

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. Slight 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 this morning to 8 PM EDT this
     evening for ANZ231>235-237.
     Small Craft Advisory from 8 AM this morning 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...Mensch
MARINE...Dooley/McMinn