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Area forecast discussion
National Weather Service Taunton Massachusetts
1036 am EDT Tue Sep 26 2017

Synopsis...
unseasonably warm and humid conditions will continue through
Wednesday, but there will be areas of overnight and early
morning dense fog. A cold front moves through southern New
England Wednesday night and then offshore during Thursday.
Moisture from Maria may enhance shower activity as the front
moves through the cape and islands. Much cooler and less humid
air will follow the front for the end of the week and weekend.
Hurricane Maria will continue to bring dangerous surf and rip
current conditions to the ocean exposed South Coast but pass
well southeast of New England by week's end.

&&

Near term /until 6 PM this evening/...

1015 am update...

Low clouds and fog are slowly but steadily breaking across most
inland areas except the CT valley, as well as across eastern
mass and southern Rhode Island on latest GOES-16 non-op prelim satellite
imagery. Observations also signaling the improving visibility
though low clouds linger a bit longer especially the closer one
gets to the coast. Improving conditions may make it to the
coast but only briefly with light east-southeast winds keeping periods of
low clouds along the immediate coast.

Based on how quickly the clouds break and how long they last
will determine how high the temps may go. Have kept similar
trends from the previous forecast, but will monitor closely
especially across eastern mass into Rhode Island.

Another issue will be whether any showers that have been passing
well southeast of Nantucket may push closer to the coast. At this
point, looks like they will remain offshore so kept previous
forecast going, but will continue to monitor.

Have updated near term forecast to bring conditions current.

Previous discussion...

Increased seas/swells on the mass eastern outer waters as well
as the Narragansett Bay entrance to 5-6 feet through Wed night.
Have extended the Small Craft Advisory for hazardous seas to
both those areas.

A concern remains that the fog may persist just off the coast
in many spots and may slip back in with a light onshore wind.
This will bear close watching. The speed at which the fog Burns
off could also have an effect on today's eventual high
temperatures.

Have also increased pops off the southeast coast to reflect showers
that continue to develop/re-develop there. Water vapor imagery
would seem to imply that this activity may be in part fueled
with moisture emanating from Hurricane Maria located some
distance east of the Carolinas. This too may need to be watched
in the event some of this activity were to encroach closer to
land (cape and islands).

&&

Short term /6 PM this evening through 6 PM Wednesday/...
***areas of dense fog likely to redevelop tonight***

Tonight...

Low clouds and areas of fog, some of which will likely be
locally dense should redevelop tonight. This from a combination
of light winds/high dewpoints and longer nights given its late
September. The next shift may need to consider another dense fog
advisory. Low temps again will mainly be in the 60 to 65 degree
range.

Wednesday...

Model cross sections indicate that the low clouds and fog may
persist a bit longer than today, especially along the coastal
plain. Nonetheless, do expect to see at least some improvement
along with partial sunshine eventually developing. High temps
should once again rise into the 80s away from the immediate
coast and it will once again be humid. Not much forcing/deep
moisture given upper level ridge still in control so generally
expect dry weather to prevail, but can not rule out a spot
shower or two Wednesday afternoon.

&&

Long term /Wednesday night through Monday/...
highlights...

* a cold front will pass across southern New England Wednesday night
into Thursday morning with scattered showers
* Maria will pass well southeast of New England, but moisture from Maria
may enhance showers over the cape and islands Thursday morning
* much cooler and less humid air will follow the cold front for
Thursday afternoon through the weekend

Medium range models depict a propensity for the large scale mid
level circulation to favor a ridge extending across the Ohio Valley
but also a series of short wave troughs that temporarily erode the
north side of the ridge. This suggests that our region may be
subject to alternating warm and cool temperatures over the next
1 to 2 weeks.

One vigorous but progressive upper trough will bring a surface cold
front through southern New England Wednesday night and Thursday
morning. This alone should suffice to mention a chance for showers.
As the front passes across the cape and islands, a consensus of
medium range models continues to suggest that moisture from Maria
becomes entrained into the front even though Maria itself appears
destined to pass out to sea well southeast of New England. The
moisture entrainment may result in some heavy downpours somewhat
reminiscent of a pre setup. Model guidance continues to suggest
showalters near zero, k indices above 30, and precipitable waters
near 2 inches as the front passes through southeast New England. It
is possible, however, that the heavier showers develop just
offshore.

Behind the surface cold front, much cooler and less humid air moves
into the region. Although temperatures will be nearly 20 degrees
cooler, this actually just brings temperatures to near seasonable
levels for this time of year.

There is a second short wave trough and secondary cold front that
moves through late Friday night into Saturday morning. There may be
enough moisture and low level convergence to support at least widely
scattered showers during late Friday night/Saturday morning.

&&

Aviation /14z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Wednesday/...

Through this afternoon...moderate confidence.
Areas of IFR-LIFR conditions may periodically continue across
the immediate coastal terminals through midday or early
afternoon, but should improve through the afternoon away from
the coast. Lower conditions should linger across Outer Cape cod
and the islands through most of the day.

Tonight...moderate confidence. Widespread IFR-LIFR conditions
expected to redevelop once again as the night wears on in low
clouds and areas of fog, some of which will be locally dense
again. This a result of a cooling boundary layer coupled with
high dewpoints and light winds.

Wednesday...moderate confidence. Widespread IFR-LIFR conditions
should gradually improve in many locations later Wed am and
into the mid afternoon. However, low clouds and fog patches may
be stubborn along the coast especially the cape and islands.

Kbos taf...moderate confidence in taf. LIFR conditions should
improve by mid to late morning, but will have to watch for
areas of fog and low clouds lingering near The Harbor through
the afternoon. A light onshore wind flow opens the door to the
risk of fog/low clouds drifting back over the airfield.

Kbdl taf...moderate confidence in taf. Low clouds and fog are
expected to give way to VFR conditions by this afternoon. The
exact timing of the improvement, however, is hard to pin
down.

Outlook /Wednesday night through Saturday/...

Wednesday night/Thursday morning...moderate confidence. Areas
of MVFR ceilings/visibilities in scattered showers except areas
of IFR ceilings/visibility in showers and fog.

Thursday afternoon through Saturday...high confidence of mostly
VFR conditions.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday/...

Today through Wednesday...high confidence.

1015 am update...

Long period southerly swell from distant Hurricane Maria will
result in 7 to 11 foot seas through Wednesday across most of the
open waters. Small craft advisories from hazardous seas continue,
including across the eastern outer waters and the Narragansett
Bay entrance. In addition, areas of dense fog will impact the
waters and result in poor visibility for mariners at times,
especially during the overnight through mid morning hours.

Outlook /Wednesday night through Saturday/...

High confidence through the period.

Swells from Maria will likely affect the southern coastal waters
through at least Friday with hazardous seas. There may be a period
of north winds late Thursday into early Friday with 25 to 30 knot
gusts, especially across the eastern and southeastern zones. Showers
and fog may lower visibilities to less than a mile across some of
the coastal waters Wednesday night into Thursday morning. Visibility
is not expected to be an issue Thursday night through Saturday.

&&

Tides/coastal flooding...
long period southerly swells will continue to propagate
northward from distant Hurricane Maria across the southern
coastal waters. This will continue to create high surf and
dangerous rip currents along ocean exposed beaches of the South
Coast, cape and islands. The high surf advisory remains in
effect through Wednesday in this region, but will likely need to
be extended through the end of the work week given the
continuation of long period swell working northward from Maria.

&&

Climate...
highs are expected to be a degree or two lower than yesterday,
while records for today are in the 89 to 95 degree range. Therefore,
not expecting any record highs to be set this afternoon,
although it will be very warm and humid away from the immediate
coast.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...high surf advisory until 6 PM EDT Wednesday for maz020-022>024.
Rhode Island...high surf advisory until 6 PM EDT Wednesday for riz006>008.
Marine...Small Craft Advisory for hazardous seas until 6 am EDT
Thursday for anz233>235-237-250-254>256.
Small Craft Advisory for hazardous seas from 6 PM this evening
to 6 am EDT Thursday for anz236.

&&

$$
Synopsis...Frank/Thompson
near term...evt/Thompson
short term...Frank
long term...Thompson

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