Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 241743
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
143 PM EDT Sun Sep 24 2017

.SYNOPSIS...
High pressure covering much of the Eastern USA will bring warm and
dry weather to Southern New England the first part of this week.
Cold front approaches southern New England during Wednesday
afternoon and triggers scattered showers. Cold front slowly moves
through southern New England on Thursday and offshore Thursday
night. Maria will bring swells to the south coast, but the center is
expected to pass well southeast of New England late in the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
140 PM update...
SKC across SNE but stratus lurking around ACK and expect this
stratus and patchy fog to move back in across Cape and Islands
toward sunset, earlier at ACK. Record heat expected in the CT
valley with unseasonably warm temps elsewhere, but sea breezes
expected along both coasts. Highs upper 80s to lower 90s away
from the coast, with temps holding in the upper 70s along the
immediate coast.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
High pressure remains over the region tonight and Monday. That means
mostly clear skies and light winds. Dew points will mostly be in the
60s much of this time, so min temps tonight will be in the upper 50s
and 60s. Expect a similar mixed layer Monday, with temps at 850 mb
of 17-18C.  So max temps should be similar to today, upper 80s and
low 90s inland and cooler near the shore.  Light flow will again
allow sea breezes to form, buffering temperatures along the
coastline.

Patchy fog will again be possible overnight and early morning,
favoring the usual inland fog spots as well as the South Coast.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights...

* Very warm temperatures persist into Wednesday
* Scattered showers Wednesday afternoon through Thursday night
* Maria will bring swells to the south coast but will sharply
  recurve out to sea southeast of New England late in the week

Tuesday...H85 temperatures 16C to 18C will support very warm
temperatures into Tuesday with surface temperatures reaching well
into the 80s throughout most of the region. The light gradient flow,
however, will set the stage for sea breezes along the coastal plain.

Wednesday through Thursday night...A surface cold front and upper
short wave trough will approach southern New England Wednesday
afternoon. We anticipate scattered showers to develop ahead of the
front Wednesday afternoon in moist, marginally unstable air mass.
Model guidance suggests showalters near zero and K indices above
30. Models have been giving a signal that tropical moisture from
Maria may become entrained in the air mass just ahead of the
front and increase the risk of a few heavy downpours, although
there is uncertainty in the timing/duration of Maria`s moisture
entrainment. The air mass appears to be unstable enough to
support isolated thunder at least for Wednesday
afternoon/evening. Due to the upper shortwave trough having to
erode a very strong upper level ridge, the surface cold front
will probably move slowly across southern New England and may
not pass offshore until Thursday night. Thus, we anticipate
scattered showers to persist Wednesday night into Thursday
night. With tropical moisture from Maria and precipitable waters
1.7 to 2 inches, some the showers could contain very heavy
downpours anytime late Wednesday to Thursday night.

The air mass remains mild Wednesday into Thursday, but clouds will
likely temper the high temperatures some. May still experience 70s
to near 80 on Wednesday and probably mid to upper 70s on Thursday.

Friday...Model consensus has the cold front passing offshore to the
southeast of New England Friday morning, and Maria passing well
southeast of our region. This will result in drier and cooler air
moving into southern New England, although showers may linger into
the morning for a while in southeast sections. Maria will become
embedded in the westerlies on the leading edge of the mid latitude
upper trough and likely pass out to sea well southeast of New
England. H85 temperatures drop about 10C, and Friday`s high
temperatures will be noticeably cooler, albeit just closer to
normal, even with plenty of sunshine and downsloping winds.
Dewpoints in the upper 60s and 70s for most of the week will
drop into the 40s most locations during Friday.

Saturday...For now Saturday looks to be dry with near normal
temperatures and very low humidity.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday/...

Through 00z...VFR, but areas of IFR stratus and patchy fog
redeveloping at ACK and possibly portions of Cape Cod.

Tonight...Expect stratus and fog across Cape/Islands which may
expand along the south coast during the night but confidence is
lower here. VFR elsewhere, except for patchy fog upper CT
valley.

Monday...High confidence. VFR, but areas of IFR stratus and
patchy fog may linger over Cape and Islands into the afternoon.
Uncertain timing of improving conditions over the Cape.

Monday night. Moderate confidence. IFR stratus and patchy fog
may become more expansive across SNE but areal extent
uncertain.

KBOS TAF...High confidence. Sea breeze redevelops by 15z Mon.

KBDL TAF...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Confidence...High.

Tuesday...Mostly VFR except for patchy early morning fog.
Wednesday...Mostly VFR but scattered MVFR ceilings/visibilities
in showers, main during the afternoon. Wednesday night through
Thursday...MVFR ceilings and areas of IFR ceilings and
visibilities in scattered showers and fog.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today...High confidence.

High pressure over the Eastern USA will bring light wind to the
waters. The remnants of Jose well south of our area may favor a
light east wind over our waters. Daytime heating of land areas will
favor a sea breeze along the immediate coast.

Locally dense fog may start the day over the waters around Cape Cod
and Islands. This will mean a period of poor visibility to start the
day.  This fog should thin and dissipate over most waters by midday
or early afternoon.

Most seas are at 2-3 feet with a period of 10-15 seconds. This is
leftover swell from Jose. Higher seas are found on the southern
outer waters, and an additional south swell of 3-4 feet leading
north from Maria will start showing itself in our southern waters
later in the day.  A High Surf Advisory remains in place in
anticipation of this swell.

Tonight and Monday...

Light wind continues under high pressure.  Seas will continue to
build through the period as increasing swell moves north from Maria.
South swell should reach 6-8 feet by Monday afternoon, affecting all
of our exposed southern shoreline and possibly the southern beaches
of the Outer Cape late Monday. Expect high surf and dangerous rip
currents as a result of this swell.
Outlook /Monday Night through Thursday/...Confidence...High

Relatively light winds are expected through this period. However,
swells from Maria will propagate into the southern coastal waters,
beginning late Sunday night or Monday. Small Craft Advisories will
likely need to be extended due to rough seas for the waters south of
the MA and RI coast for all of this period.

The swells from Maria will likely produce another round of high surf
and dangerous rip currents.

OUTLOOK...Monday night through Thursday

Confidence...High

Relatively light winds are expected through Thursday. However,
swells from Maria will impact the south coastal marine zones, and
Small Craft Advisories will likely be needed due to rough seas.

The swells from Maria will likely produce continuing high surf and
dangerous rip currents, probably lasting most of the week.

&&

.TIDES/COASTAL FLOODING...
High Surf Advisories remain in effect through Monday along the south
coast and the Outer Cape east coast. Swells from Maria will likely
increase the surf and associated rip current risk across our ocean-
exposed south coast starting later this afternoon and continuing
through the week. This will be true even though Maria may eventually
recurves out to sea well southeast of New England.

&&

.CLIMATE...
Best chance for record high temps will be Today and Monday, when
records are 85-90. Records jump up Tuesday to 89-95, while less
mixing will lead to lower max temps. So the chance for new records
diminishes Tuesday. The current record max temps for the three days
are

BOS  90/1959  89/1926  95/1881
ORH  85/2010  85/1970  91/1930
BDL  89/1959  90/2007  93/2007
PVD  87/1959  89/1920  89/2007

Also...  Dew points in the 60s, while high for this time of year,
are not unprecedented. The daily extreme high values for dew points
are still in the low 70s, except for a couple of 68 and 69 values at
Worcester.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 6 PM EDT Monday for MAZ020-022>024.
RI...High Surf Advisory until 6 PM EDT Monday for RIZ006>008.
MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT Monday
     for ANZ235-237.
     Small Craft Advisory for hazardous seas until 6 PM EDT Monday
     for ANZ254>256.

&&

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


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