-- Discussion containing changed information from previous version are highlighted. --
038
FXUS61 KBOX 202359
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
759 PM EDT Fri Sep 20 2024

.SYNOPSIS...
Offshore low remains stagnant through Saturday and begins to
move to the southeast Sunday and continue through Monday. While
dry weather is expected Sunday through Tuesday, cloudier
conditions and onshore breezes are expected, along with a risk
for higher surf through Monday. Rain chances then increase again
for midweek as a frontal system moves in from the Great Lakes.
Near to slightly below normal temperatures are expected into
midweek.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
-- Changed Discussion --
750 PM Update:

Offshore gale just southeast of 40N/70W continues to remain
nearly stalled out. While central and eastern portions of New
England have been blanketed in stratus all day, we are now
starting to see stratus expand westward into western New
England. Thus overall, a pretty dreary night across the board.

So far the steadiest light rains have been south and east of
I-95 along an inverted 700-mb trough which trails northward into
the Gulf of Maine. Though can`t entirely rule out an
intermittent light shower into interior portions of Essex County
into Greater Boston and Metrowest, at least through midnight
the steadiest rains should remain confined to the tip of Cape
Ann southward into SE MA and the Cape and Islands with little
westward progress. Later in the overnight into early Sat AM,
there are indications that the 700 mb trough very slowly pivots
west and that should bring steadier light rains into much of eastern
MA; that said, I view the 18z NAM rain/QPF depiction as being a
bit overdone in both its magnitude and northward extent
(verbatim, into Boston and northeast MA).

Finally, continuing to monitor coastal flooding with the onshore
NE flow bringing a currently observed storm surge of 1.6 ft at
Boston Harbor as of 734 PM. We`re now approaching low tide but
next high tide takes place at Boston Harbor around 158 AM. We
did have a few reports of minor coastal flooding in Scituate,
Sandwich and Quincy with this afternoon`s high tide, and we
could see similar minor coastal flooding late tonight/overnight
associated with that high tide. Coastal Flood Advisories
continue with no changes.

Previous discussion:

The low to the south of Nantucket will remain stalled through the
overnight hours. Rain is expected to continue over the Cape and
Islands into parts of SE MA and RI, with cloud cover remaining for
much of eastern MA. Not much cooling expected overnight tonight with
the persistence of this cloud cover over much of the area, so lows
are expected to remain mostly in the upper 50s/lower 60s for
southern New England, with the cooler lows primarily in central MA.
Parts of the Cape could see about an inch of rain tonight
(Provincetown, Chatham), but overall rainfall amounts diminish
westward. Northeasterly winds expected to persist during this
period.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Rain should persist for southeastern MA and the Cape/Islands for
much of the day tomorrow. Highs are expected to be in the lower to
mid 60s for much of eastern MA into central MA due to persistent
cloud cover limiting daytime heating. Slightly warmer in the CT
River Valley with highs in the upper 60s. The low is expected to
begin moving away from southern New England Saturday afternoon into
the evening hours. Latest guidance is quite confident in this
timing. Lows Saturday night should be slightly cooler out west in
the mid to lower 50s, with eastern MA still sitting in the lower 60s
and upper 50s. The pressure gradient decreases a bit as a result,
favoring winds becoming less gusty and more northerly rather than
the NE pattern we`ve been seeing going into Sunday morning.
Northerly winds should bring drier air down, progressing from the NW
to the SE starting around the end of this period, helping to clear
out the rain and cloud cover from the past few days.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Highlights:

* While dry, still a cloudier-than-not period with continued NE
  breezes thru Tue. High surf and/or elevated risk for rip currents
  as well thru at least early next week, and minor coastal flooding
  on east facing coasts again possible into Sun.

* Frontal system around Wed or Thurs offers the next chance for
  rains, although the timing is still uncertain.

* Temps near to slightly cooler than normal.

Details:

Sunday through Tuesday:

Slow-moving offshore low pressure will gradually shift southward
through this period; however a ridge of high pressure extending from
Downeast Maine into the spine of the Berkshires will maintain a
continued onshore ENE flow. Although the risk for light coastal
showers will have diminished with dry weather predominating, all in
all Sunday through Tuesday projects as a more-clouds-than-sun look
with ENE breezes keeping east coastal area considerably cooler than
further inland. Highs mainly in the 60s to lower 70s, with cooler
values near the eastern coast. With better chances at some
radiational cooling inland, lows each evening should be cooler
inland, in the upper 40s to low 50s; with coastal low temps in the
middle 50s.

With the continued northeasterly flow and elevated seas, there will
continue to be a risk for rip currents and high surf with a need for
rip current and/or surf headlines for the eastern coast. While astro
tides lower each day, we could still have pockets of minor coastal
flooding and/or washover onto vulnerable shoreline roads, especially
for Sunday, with less of a risk as we move into early next week.

Wednesday and Thursday:

Although midweek should again feature more clouds than sun, rain
chances again return at some point either Wed or into Thurs as a
frontal system tries to move in from the Gt Lakes region. Which
period or period(s) may offer the best chances for rain is still a
bit uncertain and stayed fairly close to NBM rain chances, with
better chances (higher-end Chance/40-50%) around Wed night into
Thurs.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Forecast Confidence Levels:

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

06z TAF Update:

Tonight: High confidence in TAF/trends but moderate on exact
timing.

MVFR to IFR are common early tonight, with IFR/LIFR across the
Cape and Islands. Expect these conditions to continue tonight,
perhaps with one-category degradation in eastern MA, although
steadiest rains should remain over the Cape airports. Toward
daybreak, better chances for rains into eastern MA. Dry weather
generally expected west of ORH. NE winds around 15-20 kt with
gusts 25-35 kt highest Cape and Islands.

Tomorrow...Moderate Confidence

Interior terminals expected to be MVFR for most of the day.
Lower ceilings linger at BOS, PVD, and Cape/Island terminals
(MVFR/IFR ~ 1000 feet), slowly improving from the north going
into 00z tomorrow evening.

Tomorrow Night...Moderate Confidence

Gradual improvement to VFR ceilings from the north progressing
south. MVFR expected to linger for RI, Cape/Islands, and partly
BOS moving into Sun AM.

BOS TAF...High Confidence

Remaining between MVFR and IFR tonight into Saturday. Appears
better chances for rains around 11z and continue until midday
before shifting southward.  NE winds continue, gusting up to 30
knots tonight before mostly remaining around 25 knots Saturday.
Should see improvements to VFR by Saturday evening.

BDL TAF... High Confidence

Deterioration to MVFR ceilings tonight, before trending VFR
ceilings around Sat aftn.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local MVFR possible. Breezy.

Sunday Night through Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: Mainly VFR, with areas MVFR possible.

Tuesday Night: Mainly VFR, with areas IFR possible. Slight
chance SHRA.

Wednesday: Mainly VFR, with areas IFR possible. Chance SHRA.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Saturday Night

Gale force winds continue to be likely through tonight into
early tomorrow morning across the northern and southern waters
with persistent strong NE winds. Despite decreasing from gale
strength, Small Craft Advisories will likely be needed for these
same areas. Small Craft Advisories will remain for Narragansett
Bay and Boston Harbor through 12z Saturday. Winds are expected
to start weakening a bit after 12z Saturday, and wave heights
should begin to come down moving into Saturday night with
weakening winds and with the stagnant low beginning to move away
from south of Nantucket. Wave heights should go from 11 to 12
ft Saturday to 7 to 10 ft that night.

Previous discussion:

Today through Saturday

Dangerous marine conditions through Saturday as an area of low
pressure south Nantucket continues to produce a persistent fetch
over the coastal waters. Persistent northeast winds will result
in building seas and significant wave heights from 10 to 13 feet
off the coast of Wellfleet. The eastern waters may see wave
heights from 7 to 10 feet over the near-shore marine zones. For
the south coastal waters the near-shore zones will be in the 4
to 6 foot range the outer marine zones in the 6 to foot range.

Northeast winds strengthen to gale force over the south coastal
waters today with some gusts up to 40 knots possible. A Gale
Warning remains in effect through this evening. Winds weaken
somewhat tonight into tomorrow but still remain elevated with
gusts up to 30 knots. Small Craft Advisories will likely be
needed through the weekend.

Outlook /Sunday through Wednesday/...

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Rough seas up to 12 ft. Slight chance of rain
showers.

Sunday Night: Winds less than 25 kt. Rough seas up to 12 ft.

Monday: Winds less than 25 kt. Rough seas up to 10 ft.

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

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

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.

&&

.TIDES/COASTAL FLOODING...
Coastal Flood Advisories have been extended for coastal eastern
MA including the Islands right through the weekend. Offshore
low pressure will continue to generate a long duration period of
NE wind gusts of 25 to 30 knots through the weekend. This will
generally result in a 1 to 1.5+ foot storm surge along our ocean
exposed east facing beaches. This long duration NE flow will
allow for 7 to 13 foot seas across our eastern open waters and
guidance is often underdone in these setups. This combined with
high astro tides will result in widespread minor coastal
flooding during the Saturday and Sunday midday high tide
cycles...with Saturday/s being the one of greatest concern given
the higher astro tide. There also will be pockets of scattered
minor coastal flooding with the overnight/very early Saturday
morning high tide...but less widespread than the expected midday
cycles because of lower astro tides.

In addition...because this is a long duration event there is
also concern for beach erosion. This is especially true for
areas that were hard hit by the storms of last winter.

Lastly...we have gone with High Surf Advisories for all ocean
exposed beaches along both coasts given the rough seas offshore.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...High Surf Advisory until 7 PM EDT Saturday for MAZ007-019-020-
     022>024.
     Coastal Flood Advisory from 11 PM this evening to 5 AM EDT
     Saturday for MAZ007-015-016-019-022>024.
     Coastal Flood Advisory from 11 AM to 5 PM EDT Saturday for
     MAZ007-015-016-019-022>024.
     Coastal Flood Advisory from noon to 6 PM EDT Sunday for MAZ007-
     015-016-019-022>024.
RI...High Surf Advisory until 7 PM EDT Saturday for RIZ006>008.
MARINE...Small Craft Advisory until 8 AM EDT Saturday for ANZ230-236.
     Gale Warning until 8 AM EDT Saturday for ANZ231>235-237-250-
     251-254>256.
-- End Changed Discussion --

&&

$$

SYNOPSIS...Loconto/Hrencecin
NEAR TERM...Loconto/Hrencecin
SHORT TERM...Hrencecin
LONG TERM...Loconto
AVIATION...Loconto/Hrencecin
MARINE...Frank/Loconto/Hrencecin
TIDES/COASTAL FLOODING...Frank