557
FXUS61 KBOX 211124
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
724 AM EDT Thu Aug 21 2025

.SYNOPSIS...
Drier conditions with lingering cloudy skies and increasing
winds are expected for Thursday. 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 areas of coastal flooding and
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 also expected impacts. Seasonable weather expected
Friday and Saturday with breezy conditions. Turning more
unsettled for Sunday through Tuesday with daily chances for
showers and thunderstorms.

&&

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

* Winds increase from the NE today, especially over the Cape/Islands

* Hurricane Erin will continue to pass well offshore of southern New
  England, but high surf, dangerous rip currents, coastal flooding
  and beach erosion are expected to impact the coastline

Rain continues to move through RI, CT, SE MA, and across Cape Cod
and the Islands this morning. This will continue to move south
heading into mid-morning, clearing up across much of southern New
England. Some showers/sprinkles may linger over the Cape and Islands
along with some patchy fog, but this should clear heading into the
afternoon. Cloudy skies are expected to remain through the day with
occasional breaks of sun and some improvement expected heading into
the evening hours. Highs today are expected to be in the low 70s and
upper 60s.

High pressure settled over New England and into Canada combined with
the approach of Erin will result in a tightening pressure gradient.
As a result, winds will start to amplify today across much of the
region, but especially over the waters, Cape Cod, and the Islands.
Gusts to 30 knots (35 mph) will be possible in the afternoon across
these areas. Elsewhere, gusts to 25 mph can be expected, diminishing
further west and inland. HREF mean 925 mb winds approach 35 knots
over the Cape/Islands, and with daytime mixing, surface gusts of 40-
45 mph aren`t out of the question by the late afternoon/evening. For
this reason, a Wind Advisory is in effect over those areas starting
5 PM tonight. Along with these strong winds, dangerous rip currents
and high surf remain a threat, especially along south-facing beaches.

&&

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

* Winds continue to amplify through tonight into Friday, though they
  begin to diminish heading into Friday evening as Erin pulls away

Generally dry conditions expected tonight, though strong winds
persist over SE MA and over the Cape and Islands as the gradient
between the high over the region and Erin offshore remains in place.
Model soundings continue to indicate mixing to around 925 mb where
winds are shown to be getting up to 40 knots. These values are
mainly across Cape Cod and the Islands, but breezy conditions across
SE MA into RI can still be expected overnight. Lows tonight are
expected to be in the low 50s across the interior where these
nocturnal winds won`t be as strong, and in the low 60s across
eastern MA where these continued NE winds are expected.

Erin continues its passage to the northeast Friday. As it does so,
the gradient over the region will start to slacken and winds will
begin to diminish in the afternoon. However, coastal flooding, rip
currents, and high surf will continue to be threats impacting the
region. An elevated risk for minor coastal flooding on the Islands
will be notable particularly during high tide tonight. See the
coastal flooding section of this discussion for more
information.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Messages:

* 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

* Unsettled conditions expected for the start of next week

Winds associated with Erin will continue to drop off heading into
Friday night, with gusts diminishing to only around 10 mph
overnight. The marine/coastal threats associated with Erin will
persist heading into Saturday as it will take some time for the
waters to calm a bit after Erin`s exit.

Temperatures begin to warm to more seasonable values heading into
the weekend. Temperatures at 925 mb return to around 20C after
getting down to 10C, and surface temperatures may end back up in the
mid 80s for Saturday. Lows rise into the low 60s to start next week.
The pattern turns more unsettled Sunday through Monday night as a
cold front approaches the region and a subtropical wave makes its
way up the east coast. With the combination of this front and wave
moving into the region possibly Monday night, this could lead to
scattered to numerous showers and storms. Ensembles are showing the
chance for some instability building Monday afternoon that would
help support this risk for storms, but given this is multiple days
away, confidence is low at this time regarding whether or not this
may end up severe. Though unsettled, more seasonable temperatures
can be expected to start off the week as highs sit mostly in the
upper 70s ahead of the expected cold front.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

12z TAF Update:

Thursday...High confidence.

MVFR breaking out into VFR towards the afternoon, with clearing
expected earlier across the interior and later closer to the
Cape and Islands. Overall guidance has slowed down clearing
compared to previous runs. NE winds sustained from 8 to 12 kts,
gusting 20-25 kts for much of the region through the day. Gusts
to 30 kts over the Cape and Islands.

Thursday Night...High confidence.

VFR. Gusty NE winds continue 20-25 kts for BOS/PVD and should
diminish across interior terminals. Stronger for the
Cape/Islands with gusts up to 40 kts possible.

Friday...High confidence.

VFR. N winds sustained at 10 kts across much of the
region, 25 kts over the Cape and Islands in the morning.
Gusts start around 20 kts for BOS/PVD and up to 40 kts over
the Cape and Islands before overall winds diminish heading into
the afternoon and evening.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night through Saturday Night: VFR. Breezy.

Sunday: VFR. Breezy. Slight chance SHRA.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA, slight chance TSRA.

Monday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Friday...High confidence.

Large southerly swell from Hurricane Erin will result in
increasing seas approaching 11 ft for the southern outer waters
this morning. This will continue to ramp up through Friday,
extending northward across the eastern zones.

A High Surf Advisory remains in effect for southern coastal
areas, including the Cape and Islands. Waves up to 20 feet are
possible for the southern outer waters off the south coast and
off Martha`s Vineyard/Nantucket, gradually decreasing Friday.
Rip currents will become a significant concern as the week goes
on with this elevated surf through at least the first half of
the weekend. Eastern zones are included in the High Surf
Advisory starting this afternoon, including portions of the
south and north shores.

A Gale Warning which will go into effect this morning. There is
an increasing risk for gusts to 40 kts as the gradient between
the high pressure over southern New England and passing Erin
will tighten greatly. The northern outer waters are included in
the Gale Warning for Friday night during the period of gusts
35-40 kts. Elsewhere will see Small Craft Advisories starting
this afternoon to cover the high waves and elevated wind gusts.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Rough seas up to 13 ft.

Saturday: Winds less than 25 kt. Rough seas up to 9 ft.

Saturday Night: Winds less than 25 kt. Areas of rough seas.

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

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.

&&

.TIDES/COASTAL FLOODING...
Key Messages:

* Significant beach erosion on south facing ocean beaches.
* Coastal Flood Advisory for Martha`s Vineyard and Nantucket for
  Minor to perhaps Moderate coastal flooding.

The main concern is erosion along south facing ocean beaches,
especially along the south coasts of Martha`s Vineyard and
Nantucket, due to persistent long-period southerly swells that will
continue to build this week and peak on Friday, before slowly
subsiding Saturday.

Breaking waves on the ocean beaches could get as high as 10 to 15
feet, resulting in significant beach and dune erosion or loss. It is
tough to determine how much loss could occur but this could rival
what we normally see with stronger nor`easters during the winter.
Both of these islands have already seen significant beach, dune, and
shoreline loss over the past few winters and are especially
vulnerable to further loss.

The high tides of concern for coastal flooding are late Thursday
night and late Friday night, mainly on the northeast facing shores
of Martha`s Vineyard and Nantucket where we will issue Coastal Flood
Advisories. Minor coastal flooding (up to one foot deep) should
occur in the more vulnerable sections of Nantucket Harbor, Edgartown
Harbor, Vineyard Haven, and Oak Bluffs around high tide from a storm
surge of 1 to 1.5 feet and seas up to 8 feet on Nantucket Sound late
Thursday night. Models may be too quick to reduce the surge and
waves late Friday night, so we think another round of minor coastal
flooding is likely in these same areas.

If we see a surge closer to 2 feet, which would be a reasonable
worst case for both high tides, then we could see some lower-end
Moderate flooding (1 to 3 feet deep) in more vulnerable areas near
Nantucket Harbor, but this seems unlikely at this time. For the
Vineyard, even a 2 foot surge would keep impacts in the Minor
category, although more low lying areas near Edgartown Harbor would
be affected.

Elsewhere, no significant coastal flooding is expected along the E
MA coast or South Coast, but water levels could reach Action stages
along portions of both coasts due storm surge of around one foot
combined with somewhat high astronomical tides. We would be more
concerned if we had stronger pressure falls and higher surge ahead
of the hurricane, or higher seas into the eastern MA waters, which
are all unlikely given the track well offshore.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory from 2 PM this afternoon to 8 PM EDT
     Saturday for MAZ007-019.
     High Surf Advisory until 8 PM EDT Saturday for MAZ020>024.
     Wind Advisory from 5 PM this afternoon to 2 PM EDT Friday for
     MAZ022>024.
     Coastal Flood Advisory from 10 PM this evening to 2 AM EDT
     Friday for MAZ023-024.
     Coastal Flood Advisory from 10 PM Friday to 2 AM EDT Saturday
     for MAZ023-024.
RI...High Surf Advisory until 8 PM EDT Saturday for RIZ006>008.
MARINE...Small Craft Advisory from 2 PM this afternoon to 2 PM EDT
     Friday for ANZ230-236.
     Gale Warning from 2 PM this afternoon to 8 PM EDT Friday for
     ANZ231-232-250.
     Gale Warning until 2 PM EDT Friday for ANZ233>235-237-256.
     Small Craft Advisory from 2 PM this afternoon to 8 PM EDT
     Friday for ANZ251.
     Gale Warning until 8 PM EDT Friday for ANZ254-255.

&&

$$

SYNOPSIS...Hrencecin/Mensch/KP
NEAR TERM...Hrencecin
SHORT TERM...Hrencecin
LONG TERM...Hrencecin
AVIATION...Hrencecin/McMinn
MARINE...Hrencecin/Mensch/KP
TIDES/COASTAL FLOODING...Hrencecin/JWD