Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 261942
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
342 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 /19Z SATURDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

18z TAF Update...

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

Periods of windswept rain will impact the region through Sunday.
MVFR with IFR ceilings spreading north and west through the
evening. Potential for borderline LIFR ceilings tonight, though
lower in confidence as we do have windy conditions that
typically limit low ceilings. Low risk for a thunderstorm this 
afternoon with the higher risk for southern terminals (BDL/PVD).
TEMPOs have been included for a few hours this afternoon for 
TSRA although as convective showers shift through. 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.

Convective showers this afternoon. There is a risk for a brief
thunderstorm or pulse or two of lightning this afternoon which
has resulted in the TEMPO TSRA.

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/Mensch
MARINE...Frank/Mensch