564
FXUS61 KBOX 262331
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
731 PM EDT Sat Sep 26 2026

.WHAT HAS CHANGED...
A Flood Watch has been issued for central and eastern
Massachusetts as well as Rhode Island. Periods of rain will
continue, potentially moderate to heavy at times. Storm totals
of 2-4" with localized 5-7" are possible. Issued Flood Watch in
areas that may potentially see those higher amounts with
potential for impacts to small rivers/streams and urban/poor
drainage areas.

&&

.KEY MESSAGES...

- Strong/long duration Nor`easter will continue to bring
  damaging wind gusts, coastal flooding/beach erosion, and
  periods of heavy rain through the weekend. Rain and gusty
  winds persist into Monday.

- Marked improvement Tuesday, followed by mainly dry and warmer
  weather for the remainder of the week.

&&

.DISCUSSION...
KEY MESSAGE 1...Strong/long duration Nor`easter will continue to
bring damaging wind gusts, coastal flooding/beach erosion, and
periods of heavy rain through the weekend. Rain and gusty winds
persist into  Monday.

Impacts from this Noreaster are well underway, with satellite
imagery showing a distinct, rotating low-pressure center positioned
just to our south. Evident bands of higher cloud tops indicate
robust convection, which is being reflected on radar as convective
showers and even a few embedded thunderstorms. This afternoon, these
bands have pivoted into the South Coast and southeast MA. Expect
these conditions to persist through the evening, bringing periods of
moderate to heavy rainfall rates. Given the banded and scattered
nature of the convection, impacts will be localized, but areas
across southern MA, RI, and CT face the highest risk through
tonight. While we will continue to monitor for isolated flash
flooding under the heaviest downpours, the primary hydro threats
remain urban ponding and poor-drainage flooding. Strong NE winds
persist into tonight. Peak gusts of 4560 mph were observed along
the coast early this morning, with localized gusts of 6070 mph
across Block Island and the Cape and Islands. Expect 4555 mph
gusts, occasionally up to 60 mph to continue this afternoon, highest
along the immediate coast.

Strong to Damaging Wind Gusts:

Tonight, the low is forecast to slowly track northward, but west of
the 40/70 benchmark before taking a sharp westward turn toward the
NJ coast. As the low pivots, a potent 925mb low-level jet (LLJ)
oriented SW-NE across southern New England will strengthen to 6070
kts. This introduces a renewed risk for a period of consistently
stronger surface gusts, particularly across the South Coast, Block
Island, and portions of CT if these winds can efficiently mix down.
Gusts of 4560 mph are possible in these areas, and isolated higher
gusts along the immediate coast cannot be ruled out. As the low
shifts further west toward NJ on Sunday, the 925mb LLJ will weaken.
In response, winds will veer to the E/ENE, with surface gusts
decreasing into the 3045 mph range. The pressure gradient and
associated jet will continue to gradually weaken as the low
eventually loops back to the northeast and pushes offshore. Winds
will follow suit, with gusts finally dropping below 30 mph by Monday
night.

Prolonged Period of Steady Rain, Heavy at Times:

Abundant moisture, optimal dynamics, and marginal instability will
maintain widespread rain impacts through the remainder of this
event. Added low-level convergence along the higher terrain of the
Worcester Hills and Berkshires will continue to support periods of
moderate to heavy rain. High-resolution and global guidance
highlights a broad footprint of 24 of rain, with localized
maximums of 56 possible before the system and rain exit late
Monday. Notably, the 48-hour HREF Probability Matched Mean (PMM)
highlights areas of Rhode Island and eastern Massachusetts for
potential 57 totals. Because this is primarily a prolonged
rainfall event rather than a widespread torrential downpour, the
overall flash flood threat is somewhat limited by the lack of
widespread extreme rain rates. However, the sheer volume of water
raises significant concerns for urban and poor-drainage flooding, as
well as rapid rises on small rivers and streams. To address this
threat, a Flood Watch has been issued for Rhode Island and eastern
Massachusetts, aligning with the highest-confidence footprint for
the 57 storm totals.

Coastal Flooding:

The prolonged period of strong northeast winds and high offshore
seas will continue to result in beach erosion and coastal flooding
over multiple high tide cycles through Sunday. Storm surge values of
1 to 2 feet, perhaps briefly approaching 2.5 feet, are expected
along east-facing, ocean-exposed shorelines. Coastal Flood Warnings
remain in effect along the eastern Massachusetts coast, including
the Cape and Islands, through the Sunday night high tide cycle.
Consideration is being given to extending these headlines into the
Monday morning high tide cycle.

The combination of elevated water levels and 15 to 25 foot offshore
seas will result in minor coastal flooding, with a few pockets of
low-end moderate flooding possible during each high tide cycle.
However, the most significant impact from this long-duration event
is expected to be severe beach erosion given the persistent strong
northeast winds and large waves. Astronomical tides peak this
weekend, so coastal impacts will remain a concern even as winds
gradually diminish. In addition, water may struggle to fully drain
between successive high tide cycles, while heavy rainfall could
further exacerbate drainage and flooding issues.

Coastal Flood Advisories remain in effect for the south coasts of
Rhode Island and Massachusetts. While northeast winds are somewhat
of a mitigating factor for coastal flooding in these areas, very
large swell associated with the nor`easter to our south will
propagate northward toward the coast. Pressure falls will also
contribute to elevated water levels. Therefore, pockets of
splashover and minor coastal flooding are expected, along with minor
beach erosion through the weekend.


KEY MESSAGE 2...Marked improvement Tuesday, followed by mainly dry
and warmer weather for the remainder of the week.

The weekend`s long-duration nor`easter exits east-northeast as the
mid-level flow becomes less amplified and blocking diminishes.
Throughout the coming week, the mid-level flow becomes fairly zonal,
with a few weaker impulses passing through during the mid to late
week. These may bring a low probability of a light shower or two.

Expect marked improvements Tuesday as the decaying nor`easter exits
the region and winds shift to the northwest. With northwest flow,
anticipate lower PWATs advecting into southern New England, bringing
any lingering early morning showers to an end. While PWATs remain
somewhat elevated into the afternoon, there is little forcing to
support additional precipitation. Latest guidance has slowed the
clearing trend compared to previous runs, so clouds may hang tough
through much of the afternoon before some breaks develop later in
the day. Northwest flow will also keep temperatures a few degrees
below climatological normals, though it will be noticeably warmer
than this past weekend. Highs Tuesday reach the upper 60s to around
70 degrees.

A mid-level ridge builds across the southeastern CONUS this week,
while surface high pressure builds south of the region Wednesday
through Friday, leading to a stretch of quieter and warmer weather.
Guidance hints at a weak northern stream shortwave Wednesday night
into early Thursday, followed by a secondary shortwave Thursday
night into Friday. PWATs Wednesday night into Thursday remain below
1.2 inches and don`t really align with the best forcing. Outside of
a brief light shower, would anticipate more clouds than anything.
PWATs increase to around 1.5 inches Thursday night with the passage
of the secondary weak shortwave, when a few light showers could
brush through the region. No significant impacts are anticipated
with either disturbance. Temperatures trend warmer through the
middle and latter half of the week, though latest guidance has
trended cooler compared to previous runs. Highs generally return to
the lower and middle 70s, with Thursday potentially the warmest day
as highs reach the middle to upper 70s. As for overnight
temperatures, there is no notable cold expected, with lows generally
falling into the 50s.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

00z TAF Update...

Today through Sunday...High confidence in trends, moderate
confidence in timing.

Periods of windswept rain will impact the region through Sunday.
IFR, potential for borderline LIFR ceilings tonight, though
lower in confidence as we do have windy conditions that
typically limit low ceilings. NE wind gusts of 30 to 50 knots
expected with the strongest of those winds near the coast
tonight. Wind gusts will diminish a bit on Sunday...But still
expect NE wind gusts of 25 to 40 knots.

KBOS Terminal...High confidence in trends, moderate confidence
in timing.

Confidence lower in ceiling heights overnight tonight. There is
potential for borderline LIFR conditions. This is lower
confidence as higher winds typically limit the potential for
very low ceilings.

KBDL Terminal...High confidence in trends, moderate confidence
in timing.

Outlook /Sunday Night through Thursday/...

Monday: MVFR/IFR conditions possible. Windy with local gusts up
to 30 kt. SHRA.

Monday Night: MVFR/IFR conditions possible. Chance SHRA.

Tuesday through Tuesday Night: Mainly VFR, with local IFR
possible.

Wednesday through Thursday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through the Weekend...

* Dangerous conditions for Mariners through the weekend with NE wind
  gusts of 45 to 60 knots and seas offshore of 15-25 feet.

The strengthening early season Nor`easter will bring strong NE wind
gusts of 45-60 knots and seas offshore between 10 and 20 feet.
Seas will remain quite high Sun into Mon along with NE wind
gusts of 25 to 40 knots persisting. Main update was to extend
Storm Warnings for the waters through late morning Sunday. Once
these expire, these will be replaced by Gale Warnings for Sunday
then SCAs for Monday more likely.

Outlook /Sunday Night through Thursday/...

Monday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Rough seas up to 9 ft. Chance of rain showers.

Monday Night: Winds less than 25 kt. Rough seas up to 8 ft.
Chance of rain showers.

Tuesday through Tuesday Night: Winds less than 25 kt. Seas up
to 5 ft.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft.

Wednesday Night through Thursday: Winds less than 25 kt. Seas
locally approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory until noon EDT Sunday for CTZ002>004.
MA...Wind Advisory until noon EDT Sunday for MAZ002>006-008>014-017-
     018-026.
     Flood Watch through late Monday night for MAZ004>007-012>024-
     026.
     High Wind Warning until 8 AM EDT Sunday for MAZ007-015-016-
     019>024.
     Coastal Flood Warning until 8 PM EDT Sunday for MAZ007-015-016-
     019-022>024.
     High Surf Advisory until 8 PM EDT Sunday for MAZ007-015-016-
     019-022>024.
     Coastal Flood Advisory until 8 PM EDT Sunday for MAZ020-021.
RI...Wind Advisory until noon EDT Sunday for RIZ001.
     Flood Watch through late Monday night for RIZ001>008.
     High Wind Warning until 8 AM EDT Sunday for RIZ002>008.
     Coastal Flood Advisory until 8 PM EDT Sunday for RIZ002-
     004>008.
MARINE...Storm Warning until 10 AM EDT Sunday for ANZ230>237-250-251-
     254>256-280>283.

&&

$$

DISCUSSION...Dooley/Mensch
AVIATION...Frank/Dooley/Mensch
MARINE...Frank/Mensch