Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 252307
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
707 PM EDT Mon Sep 25 2017

.SYNOPSIS...
High pressure will remain across the northeast into Wednesday,
with warm and humid conditions. A cold front combined with
moisture from Maria may impact the Cape and islands and
southeast Massachusetts late Wednesday night into Thursday.
Behind the front, turning much cooler Thursday night through the
weekend. Hurricane Maria will bring dangerous rough surf and
rip currents to the south coast this week, before passing well
southeast of New England late this week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
705 PM update...
Stratus and areas of fog have redeveloped over the Cape/Islands
and is advancing north along the south coast. Expect low clouds
to overspread much of SNE during the night along with areas of
fog as BL cools in this high dewpoint airmass. Locally dense
fog should be confined to the south coast as BL winds turn
southerly. A dense fog advisory may eventually be needed for
some coastal communities. Otherwise, dry and mild tonight with
lows mostly in the low/mid 60s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday...
High pressure ridging remains across northern New England. Once
the fog lifts, should see mostly sunny skies away from the S
coast where clouds and patchy fog will linger.

Noting the 12Z GGEM as an outlier with a band of showers trying
to push toward the S coast Tue afternoon well ahead of
Hurricane Maria. The remaining short range models remain mainly
dry, though may see a band of scattered showers developing S and
E of Nantucket during the day.

Will be another mild and humid day, though temps will be cooler
than today with decent mixing especially away from the coast.
Expect temps to top off in the 80-85 degree range away from the
coast and in the 70s along the shore.

Tuesday night...
Models starting to signal some bands of showers out ahead of
Maria approaching the southern waters. Still model spread with
this aspect of the forecast, with most keeping mainly dry
conditions. Expect another round of low clouds and fog to
return, though will likely push further inland as winds shift to
light S-SE. Lows will be in the lower-mid 60s.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights...

* Very warm and humid Wednesday with low risk of a shower/t-storm
* Sct showers/t-storm possible late Wed night/Thu SE New Eng
* Taste of autumn Thu night into the weekend with much cooler and
  less humid weather

Models in good agreement on mid level trough moving east from the
Great Lakes and amplifying over New Eng this weekend. This will
effectively be a kicker to push Maria out to sea and also bring a
pattern change to more seasonable autumn like weather late in the
week through the weekend. Before the cooler airmass arrives, will
have to watch for potential of some showers/t-storms with locally
heavy rain late Wed night into Thu across SE New Eng.

Wednesday will be another very warm and humid day ahead of
approaching cold front from the NW. Temps well into the 80s away
from the south coast with dewpoints near 70. Some instability noted
which supports a few showers or an isold t-storm developing but mid
level lapse rates are meager which is a limiting factor.

As Maria begins to move eastward well south of New Eng Wed night
into Thu, a plume of tropical moisture will lift north into the
region and interact with an approaching front moving into New Eng.
This will likely set up a PRE late Wed night into Thu with area of
showers/t-storms with locally heavy rainfall but low confidence on
location of the heavy rainfall axis and if it extends west into New
Eng. Consensus of the deterministic guidance keeps it mostly
offshore, but ECMWF and several GEFS members bring some heavy rain
to SE New Eng. Still uncertainty so will maintain PoPs of previous
forecast and continue to monitor.

Behind the cold front, much cooler airmass will move into New Eng
Thu night and last through the weekend as mid level trough amplifies
over New Eng. Mainly dry weather, but may see some diurnal showers
on Sat under the cold pool aloft with 500 mb temps -22C. Temps
mostly in the 60s Fri into Sun with lows in the 40s. Coolest day
likely on Sat with moderating temps Sun into Mon as the trough
axis moves east and heights rise.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Tonight...Moderate confidence.
IFR/LIFR stratus and patchy fog along the south coast and
Cape/Islands will gradually spread inland tonight. Widespread
IFR stratus anticipated later tonight although low confidence on
exact timing. Areas of fog as well which may be locally dense
near the south coast.

Tuesday...Moderate to high confidence.
Mainly VFR. Areas of IFR-LIFR early across Cape Cod and the
islands due to fog, with some improvement to MVFR by around
midday. Light S-SE winds.

Tuesday night...Moderate confidence.
VFR to start, then MVFR-IFR conditions moving in again. LIFR
conditions possible across Cape Cod and the islands.

KBOS TAF...High confidence in TAF. Light sea breeze shifts to
light S from 00Z-02Z. Light S-SE wind during Tue.

KBDL TAF...High confidence in TAF.

Outlook /Wednesday through Saturday/...High confidence.

Wednesday...Areas of IFR/LIFR stratus and fog near the south
coast early, otherwise VFR. Low risk of a few afternoon showers
or an isold t-storm.

Wednesday night into Thursday...Mainly VFR, but areas of
stratus and fog possible near the south coast Wed night into
early Thu. In addition, scattered showers/t-storms may impact
the Cape/Islands and SE MA late Wed night into Thu morning with
lower conditions.

Friday and Saturday...Mainly VFR. Patchy MVFR cigs and low risk of
showers Sat.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

Light E-NE winds will continue through Tuesday as high pressure
remains near and north of the waters. As this slowly shifts
offshore, winds will remain light but become S-SE Tuesday night.

Increasing long period south swells from Hurricane Maria will
continue to push across the southern waters, with the potential
for 5 to 7 foot seas tonight increasing to 7 to 10 feet late
Tuesday and Tuesday night. SCA for hazardous seas will continue,
and have extended to Vineyard Sound and Buzzards Bay mainly
near the entrances where 5 foot seas will move in.

Areas of fog will result in poor visibility at times,
especially south and east of Cape Cod and into Nantucket and
Vineyard Sounds where visibility may lower to below 1/2 mile.

Outlook /Wednesday through Saturday/...High confidence.

Wednesday...Light winds but large southerly swell will impact
the southern waters. Reduced vsbys in fog Wed morning.

Wednesday night into Thursday night...Light winds Wed night
shifting to north Thu afternoon. Increasing N winds Thu night
with gusts 25- 30 kt possible. Large southerly swell continuing.
Some heavy rain possible over waters south and east of Cape
Cod. In addition areas of dense fog may be an issue.

Friday into Saturday...Diminishing northerly wind. Seas
gradually subsiding and may drop below 5 ft Fri night.

&&

.TIDES/COASTAL FLOODING...
Long periods swells continue to propagate north from distant
Hurricane Maria across the southern coastal waters. WNA
Wavewatch guidance continues to slowly increase the swells,
reaching up to 7 to 10 feet on the southern outer waters on
Wednesday. Increasing high surf and dangerous rip currents are
expected with these high swells.

We have once again extended the high surf advisory for the
south facing beaches for Mass and RI through Wednesday. The high
surf is likely to continue through the remainder of the week
even as Maria will likely recurve out to sea well southeast of
New England.

&&

.CLIMATE...
So far, the high temp has reached 91 degrees at KBDL, setting
the record high for today`s date. Record report has been sent,
but will be updated once final high has been reached. Also, the
high at KORH reached 85 degrees at 338 PM, tying the record high
to today`s day. The max so far at KPVD remains at 84 degrees.

Records jump up Tuesday to 89-95 degrees. However, low level mixing
lowers, which leads to lower max temps on Tuesday. At this point,
the highs at our 4 climate sites are well below the records for
9/26, mainly in the lower-mid 80s away from the coast, and around 80
at BOS and PVD.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 6 PM EDT Wednesday for MAZ020-022>024.
RI...High Surf Advisory until 6 PM EDT Wednesday for RIZ006>008.
MARINE...Small Craft Advisory for hazardous seas from 6 AM Tuesday to 6
     AM EDT Wednesday for ANZ233-234.
     Small Craft Advisory for hazardous seas until 6 AM EDT
     Wednesday for ANZ235-237-254>256.

&&

$$
SYNOPSIS...KJC/EVT
NEAR TERM...KJC
SHORT TERM...EVT
LONG TERM...KJC
AVIATION...KJC/EVT
MARINE...KJC/EVT
TIDES/COASTAL FLOODING...
CLIMATE...



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