BOX issues Area Forecast Discussion (AFD) at Aug 18, 3:59 PM EDT743
FXUS61 KBOX 181959
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
359 PM EDT Mon Aug 18 2025
.SYNOPSIS...
Canadian high pressure will bring below normal temperatures/low
humidity to the region for much of the week. A disturbance
aloft moving through on Wednesday will bring increased
cloudiness along with rain chances, although how much rain falls
is still uncertain. Large southerly swell from Hurricane Erin
will lead to high surf and dangerous rip currents for south-
facing beaches Tuesday through much of the workweek, along with
a period of enhanced northeast breezes Thursday and Friday.
Otherwise, dry weather prevails until Sunday. Temperatures will
be cooler than normal through the workweek, then begin a warming
trend by the weekend.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Key Messages...
* Unseasonably cool tonight with overnight lows in the 40s & 50s
Details...
High pressure continues to build across Quebec, bringing cooler
air down to southern New England. High temperatures this
afternoon expected to remain in the upper 60s to low 70s with
gusty northeasterly winds. Dewpoints will continue to hover in
the mid to upper 40s, allowing for comfortable humidity. Gusts
along the Cape and Islands 20 to 30 mph, but will start to drop
off into the evening and overnight hours. With few clouds in the
sky and winds becoming calm overnight, can expect some
radiational cooling to drop temperatures tonight into the mid
40s in some spots.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Key Messages...
* Another beautiful day Tuesday with low humidity & highs in the 70s
Tonight...
Tuesday looks to be an extension of today, with mainly clear
skies and high temperatures in the mid 70s. Dewpoints could be a
few degrees higher, in the low 50s vs high 40s, but the day
will remain unseasonably cool, comfortable, and dry. Will start
to see cloud cover increase into the overnight period, so low
temperatures will likely remain in the 50s across southern New
England.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Key Messages:
* Increasing clouds Wed with rain chances, although there is low
confidence on the exact placement of rains and how much falls.
Soaking rain is viewed as unlikely but possible.
* Dry weather with cooler than normal temperatures through the
workweek, warming up by the weekend.
* Large southerly swell from distant Erin will bring High
Surf/Dangerous Rip Currents to south-facing beaches through
late week.
* Northeasterly breezes become enhanced out over the Cape and
Islands Thu/Fri. Possible gale-force gusts.
Details:
Forecast challenge in this portion of the forecast is on Wed. A
shortwave trough moving through the Gt Lakes region is progged
to translate ESE through the New England/northern mid-Atlc
region on Wed, as the sprawling SW-NE ridge axis initially in
place weakens somewhat. NWP continues to vary pretty
substantially both on QPF placement and in magnitude, which
unfortunately renders a low- confidence forecast. Some solutions
offering very little to nil QPF at all with several days of dry
or at least generally dry weather winning out, while some
wetter solutions show some enhanced moisture and depict some
rather eye-popping QPF values (upwards of 2 inches in the NAM).
Did note the 12z ECMWF and its 12z ensemble have ticked up some
in today's guidance, which could be a tell in terms of where
guidance may go, and its ensembles now show a 30-40% prob of QPF
at or above 0.5" with low probs of 24-hr QPF at or above an
inch, while the other global ensembles are not nearly as bullish
or as high. Currently view the bullish NAM as a wet outlier,
and it also doesn't have support from the 15z SREF either. With
this degree of uncertainty ranging from a dry outcome to
potentially a pretty wet one, think it is best to stay the
course with a blended outcome (NBM) and let trends over the next
few model cycles dictate adjustments. Regardless, certainly
will see quite a bit of cloud cover and the potential for rain
showers, but there is still quite a bit of uncertainty on the
placement and amt of QPF that will need to be adjusted pending
trends. After Wednesday, the next best chance for rain may not
occur until Sunday as ridging reasserts itself.
TC Erin is still forecast to pass well southeast of 40N/70W by
Fri. Its main influence will be building offshore waves reaching
nearly 20 ft south of Nantucket by Fri, to go along with large
southerly swell leading to several days of high surf and
dangerous rip currents for beaches with southern exposures. With
an extended spell of dry weather and that water temps remain at
their climatologically warmest, beachgoers/swimmers flocking to
the beach could be particularly vulnerable now that we are into
late in summer and beaches become less staffed by lifeguards.
High Surf Advisories have been issued through Thurs, and we may
need to consider extending these into Fri or into part of the
weekend. NE winds will also become enhanced over southeast New
England on Thurs and into Fri, with gusts 25-30 mph over land
and the potential for gale- force gusts over the southeast
waters. The winds and wave action may also elevate the risk for
coastal beach erosion over the Islands.
Cooler than normal temps and comfortable humidity levels are
expected through at least Fri with onshore flow leading to
cooler high temps (70s) with strong diurnal ranges and efficient
radiational cooling most nights (50s). We do start a warm-up
toward the weekend with rising humidity levels but not looking
at hazardous heat or humidity.
&&
.AVIATION /20Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
18z TAF Update...
Today...High confidence.
VFR. Breezy, NE winds 7 to 15 knots with gusting 25 to 30
knots, especially near the coast.
Tonight...High confidence.
VFR. Winds diminish and become light and variable.
Tuesday...High confidence.
VFR. ESE winds 5 to 10 knots.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Wednesday through Saturday/...
Wednesday: VFR. Slight chance SHRA.
Wednesday Night: VFR. Breezy. Slight chance SHRA.
Thursday: VFR. Breezy.
Thursday Night: VFR. Windy with local gusts up to 30 kt.
Friday: VFR. Windy with gusts up to 30 kt.
Friday Night: VFR. Breezy.
Saturday: Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Tuesday Night...High confidence.
Pressure gradient weakens tonight and Tue allowing winds to
diminish below small craft advisory thresholds. However...large
southerly swell from major hurricane Erin will result in seas at
or above 5 feet for portions of our southern waters overnight
into Tuesday. In fact...they will be ramping up further into
mid-week so small craft headlines will remain posted for our
southern waters for an extended period of time. High Surf
Advisory also goes into effect Tuesday for southern coastal
areas, including the Cape.
Outlook /Wednesday through Saturday/...
Wednesday through Wednesday Night: Winds less than 25 kt. Areas
of rough seas. Slight chance of rain showers.
Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 16 ft.
Thursday Night: Strong winds with gusts up to 35 kt. Rough seas
up to 17 ft.
Friday: Low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 15 ft.
Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 11 ft.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 8 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory from 8 AM Tuesday to 8 PM EDT Thursday for
MAZ020>024.
RI...High Surf Advisory from 8 AM Tuesday to 8 PM EDT Thursday for
RIZ006>008.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230-
250-251.
Small Craft Advisory until 4 PM EDT this afternoon for
ANZ231>235-237.
Small Craft Advisory until 8 AM EDT Thursday for ANZ254>256.
&&
$$
SYNOPSIS...Loconto/McMinn
NEAR TERM...McMinn
SHORT TERM...McMinn
LONG TERM...Loconto
AVIATION...Loconto/McMinn
MARINE...Loconto/McMinn
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 18, 3:59 PM EDT----------------
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