424
FXUS61 KBOX 200724
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
324 AM EDT Wed Aug 20 2025

.SYNOPSIS...
Below normal temperatures with low humidity remain in the
region for much of this week before a warming trend kicks in at
the end of the week. A shortwave moving through today will
increase cloud cover and bring rain chances to southern New
England, with amounts still somewhat uncertain. Hurricane Erin
will pass well southeast of Nantucket on Friday, with the only
impacts being limited to southeast coastal New England. High
surf and dangerous rip currents along with beach erosion are
anticipated on south-facing beaches, dangerous marine
conditions from gale force wind gusts and high offshore waves,
and potential minor coastal flooding on the Islands are the main
impacts as Erin passes well offshore. Dry weather for this
weekend. Another chance for rain returns heading into the start
of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Messages:

* Rain expected throughout the day, especially towards the afternoon
  into the evening hours

* Heaviest rain is expected just south of the Mass Pike/along the
  CT/MA border, though other areas could see locally heavy downpours

Higher clouds are moving across the region this morning with
reflectivity registering on radar, but observation sites on the
ground are not reporting rain as dry air is keeping it from reaching
the ground.

A shortwave arrives and moves through the region today. With it,
some much-needed rainfall. Guidance has come to more of a consensus
with timing: western MA and CT will likely see rain starting in the
early afternoon hours, then this will progress eastward. There is
still some spread in rainfall totals and exact location, but
guidance has continued to trend in this area seeing the higher
totals. Across western MA starting in the Berkshires and along a
line that stretches roughly along the Mass Pike into RI and SE MA,
guidance indicates some frontogenesis that may provide additional
forcing for some heavier rainfall. This lines up with rainfall
totals across the models being higher along this stretch through
southern New England. The ECMWF has 24 hour totals up to 2.25"
around Springfield, then totals just over an inch to 1.25"
stretching southeast from there. The NAM keeps the higher totals
over the Berkshires, and the GFS follows a similar pattern to the
ECMWF, just with slightly lower values only up to 1.6". The chance
for thunder remains very low, and HREF probs have even trended down
from previous runs.

Temperatures across the region today will struggle to reach 70F and
settle more so in the low to mid 60s across much of the interior
with continued cloud cover and wet bulbing occurring once the rain
moves in. In eastern MA and RI, highs are expected to reach the low
70s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Key Messages:

* Rain lingers through tonight before clearing for Thursday

* Winds begin to pick up across much of the region, especially over
  the Cape and Islands

Rain is expected to clear out heading into Thursday, though some
sprinkles may linger over the Islands and parts of SE MA/Cape Cod
into the early afternoon hours. Cloudy skies remain across much of
the region, breaking out heading into the evening hours across much
of the interior.

High pressure affixed over Canada combined with the approach of Erin
will result in a tightening pressure gradient that will continue
heading into Friday. Winds will start to amplify Thursday across
much of the region, but especially over the waters, Cape Cod, and
the Islands. Gusts to 30 knots will be possible in the afternoon
across these areas. Dangerous rip currents and high surf remain the
main threats across south-facing beaches through this period and
past it due to the southerly swell from Erin.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key Messages:

* Erin will pass well offshore of southern New England Friday, but
  high surf, dangerous rip currents, gale-force wind gusts, and
  possible beach erosion will be a concern through the end of this
  week

* Warming trend for the weekend will bring temperatures back to more
  normal values

* Another chance for some rain arrives at the start of next week

The main story for this period of the forecast is the dangerous to
life-threatening surf and rip current risk across our south-facing
beaches. This elevated risk is due to the passage of Hurricane Erin
far to our southeast Friday, which will be churning up significant
swell that will eventually make its way to our coasts. The gradient
between Erin and the Canadian high pressure settled over southern
New England will lead to amplified NE winds over the Cape and
Islands that could also have gale-force gusts. Model guidance is
indicating winds at 850 mb around 45 to 50 kts over the Cape
and Islands by Friday morning and even up to 55 kts at 925 mb.
NBM 75th percentile surface gusts reach 40 to 45 kts over
Nantucket and the outer Cape, and especially over the waters.
Aside from the Cape and Islands, the rest of southern New
England can expect a generally breezy Friday before the gradient
slackens with Erin`s influence diminishing heading into
Saturday as it moves further into the Atlantic.

Temperatures begin to warm to more seasonable values Friday heading
into the weekend. Temperatures at 925 mb return to around 20C after
getting down to 10C, and surface temperatures end up rebounding into
the low 80s and upper 70s for the weekend. Lows mostly sit in the
mid to upper 50s, rising into the low 60s to start next week. The
next chance for some rain arrives sometime Sunday into Monday as a
front moves into the region associated with a trough settled over
Ontario digs further south into the Great Lakes. Lows may decrease a
few degrees Monday night compared to Sunday night as a result of
this front`s passage, along with slightly lower daytime highs for
Tuesday.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

06z TAF Update:

Rest of Tonight: High confidence.

VFR. ESE winds around 5 knots.

Wednesday and Wednesday Night...High confidence in trends,
moderate confidence in timing and placement of SHRA.

VFR maintained through 15-17z. Periods SHRA then break out
18-20z for western airports which move east/southeast after
21z. Ceilings decrease to at least MVFR with visbys 1-6 SM in
SHRA. It remains somewhat uncertain where the
steadiest/heaviest rain may fall, although guidance continues to
trend towards ORH- BAF- BDL area. SHRA then slips south/west
for overnight, although ceilings still likely to be low-end MVFR
to IFR. NE winds around 5-10 kt.

Thursday...High confidence.

MVFR breaking out into VFR around mid-morning through the early
afternoon. NE winds sustained from 8 to 12 kts, gusting to 20
kts for much of the region. Gusts to 30 kts possible over the
Cape and Islands.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

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

Friday Night: VFR. Windy with local gusts up to 35 kt.

Saturday: VFR. Breezy.

Saturday Night: VFR.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Thursday...High confidence.

Large southerly swell from Hurricane Erin will result in seas
to 7 ft today and up to 10 ft by tonight. This will continue to
ramp up through mid-week. For this reason, Small Craft
Advisories will remain in effect across the southern waters
through tonight. A High Surf Advisory also remains in effect
for southern coastal areas, including the Cape and Islands. Rip
currents will become a significant concern as the week goes on
with this elevated surf. A Gale Watch has also been hoisted
starting tomorrow due to the risk for gusts to 40 kts as the
gradient between the high pressure over southern New England and
passing Erin will tighten greatly. This will likely be
converted into a Gale Warning with the next forecast cycle.

Outlook /Thursday Night through Sunday/...

Thursday Night: Moderate risk for gale force winds with gusts
up to 40 kt. Rough seas up to 18 ft. Slight chance of rain
showers.

Friday: Moderate risk for gale force winds with areas of gusts
up to 45 kt. Rough seas up to 17 ft.

Friday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 13 ft.

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Rough seas up to 11 ft.

Saturday Night: Winds less than 25 kt. Local rough seas.

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 8 AM EDT Saturday for MAZ020>024.
RI...High Surf Advisory until 8 AM EDT Saturday for RIZ006>008.
MARINE...Gale Watch from Thursday morning through late Friday night for
     ANZ231-232-254-255.
     Gale Watch from Thursday morning through Friday afternoon for
     ANZ233>235-237-256.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ254>256.

&&

$$

SYNOPSIS...Hrencecin
NEAR TERM...Hrencecin
SHORT TERM...Hrencecin
LONG TERM...Hrencecin
AVIATION...Hrencecin
MARINE...Hrencecin