Harwich, Massachusetts Weather Forecast Discussion

320
FXUS61 KBOX 260521
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
121 AM EDT Fri Sep 26 2025
.SYNOPSIS...
Widespread showers and a few thunderstorms are expected into this
evening as a frontal system moves into the region. Locally heavy
rainfall may produce street flooding, and can`t rule out an isolated
strong to severe storm in western New Eng. Improving conditions
Friday with increasing sunshine and warm conditions. The weather
pattern is mostly dry this weekend into next week, but watching
showers to the south may impact the region Saturday night into
Sunday. Mostly warm conditions expected into early next week, then a
strong cold front will deliver a fall airmass by next Wednesday
with temperatures well below normal.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
120 AM update...
Last of the showers will be exiting the Cape/Islands during the
next hour with dry conditions through daybreak, but may see an
additional brief shower over Nantucket. otherwise, patchy fog
may develop in the interior as skies partially clear.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Tomorrow and Tomorrow Night
Key Messages:
* Warm and humid Friday
* Trending cooler/drier into the weekend
A secondary pulse of shortwave energy crosses southern New England
during the day Friday. Redeveloping low-level southwest flow ahead
of this feature will promote warm air advection, maintaining 925 mb
temperatures in the 1718C range. This will translate to surface
highs in the upper 70s to lower 80s, several degrees above normal.
Despite the mid-level energy, dry air aloft should suppress any
shower activity. Still, a stray shower cannot be ruled out across
southeastern MA where somewhat deeper moisture lingers. Overall,
expect a warm, quiet day with a mix of sun and clouds.
Friday night, west to northwest flow develops as the shortwave exits
offshore. This will usher in cooler and drier air, with PWATs
falling below 1 inch. 925 mb temps dip into the 1012C range. With
clear skies and light winds, efficient radiational cooling will
allow lows to fall into the low to mid 50s across much of the
interior, with upper 50s to lower 60s closer to the coast.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Messages:
* Saturday remains dry during the daytime hours, but chances of
  showers Saturday night into Sunday morning.
* Above normal temps this weekend into Monday, then turning much
  cooler by Wed with a touch of fall
* Humberto expected to remain offshore next week
Expecting the daytime hours of Saturday to remain warm and dry, but
continuing to watch a stream of moisture move northward into
southern New England Saturday evening. GFS remains the most
aggressive (PWATs > 2") and brings a period of showers into the
region Saturday night into Sunday; however, model discrepancies
remain quite large, so confidence is not high at this time. Based on
ensemble probs of 0.1" QPF, we have chance showers south of the MA
Pike Saturday night into Sunday morning. If showers do develop temps
will be several degrees cooler than current forecast (likely in the
60s), but 70s if it remains dry. Warm weather continues into Monday
with potential for 80+, then a cold front pushes southward on
Tuesday, which will bring a fall airmass by Wednesday as a strong
high pressure builds to the north.
A Canadian high and strong front early next week should keep
Humberto offshore. Latest global ensemble tracks are in agreement
that Humberto will remain well to the south before curving offshore.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z TAF Update
Through 12z...
MVFR-IFR near the coast, otherwise improving to VFR further
inland but may see patchy fog develop. Winds shift to W 5-10 kt.
Today...High Confidence.
Patchy MVFR cigs over Cape/Islands early, otherwise VFR with
gradual clearing but diurnal CU developing this afternoon. W
wind 8-15 kt.
Tonight and Saturday...High Confidence.
VFR. Winds becoming light NW tonight. Light winds Sat with sea-
breezes developing.
KBOS Terminal...High confidence.
KBDL Terminal...High confidence.
Outlook /Saturday Night through Tuesday/...
Saturday Night through Sunday: VFR. Slight chance SHRA.
Sunday Night through Monday Night: VFR.
Tuesday: Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Friday Night...High Confidence
Seas build to 56 feet across the outer coastal waters overnight,
maintaining Small Craft Advisory conditions through Friday morning.
Conditions gradually improve during the day Friday as seas subside
and winds ease from the west/southwest. A dry cold front crosses the
waters Friday night, shifting winds to the north/northwest with
speeds and gusts generally 10 kt or less. Overall, relatively quiet
boating conditions are expected late Friday night into Saturday
morning.
Outlook /Saturday Night through Tuesday/...
Saturday: Winds less than 25 kt.
Saturday Night: Winds less than 25 kt. Chance of rain showers.
Sunday through Sunday Night: Winds less than 25 kt. Slight
chance of rain showers.
Monday: Winds less than 25 kt.
Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.
Tuesday: Winds less than 25 kt. Areas of rough seas. Slight
chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT early this morning for
     ANZ231-251.
     Small Craft Advisory until 6 AM EDT early this morning for
     ANZ232>234.
     Small Craft Advisory until 8 AM EDT this morning for ANZ250-
     254.
     Small Craft Advisory until 10 AM EDT this morning for ANZ255-
     256.
&&
$$
SYNOPSIS...RM
NEAR TERM...RM/JWD
SHORT TERM...RM
LONG TERM...McMinn
AVIATION...KJC/RM
MARINE...KJC

NWS BOX Office Area Forecast Discussion