Area Forecast Discussion
Issued by NWS Boston, MA

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504
FXUS61 KBOX 230749
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
349 AM EDT Sat Sep 23 2017

.SYNOPSIS...
Jose southeast of Nantucket will slowly drift back to the southwest
the next few days. This will maintain strong winds, rain and rough
seas today, which then diminish as the storm weakens this weekend.
Clearing skies will move in from the west tonight and Sunday.
High pressure will bring unseasonable warm weather for early to
mid next week.  Maria is expected to pass southeast of New
England late in the week with strongest winds well offshore.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

The remnants of Jose continue to drift southeast away from Southern
New England.  Overnight satellite imagery shows clouds across much
of the region, but also some clearing over the Berkshires.

Outside of Southern New England, the big story is longwave high
pressure with heights well about September normals. The surface
reflection of this high is bringing fair dry weather from Northern
New England to the Great Lakes and much of the South. We expect this
high to build over Southern New England this weekend, bringing a
trend to above normal temperatures.

For today this means a clearing trend from west to east, except
along Cape Cod and the South Coast where low clouds from Jose may
hang tough through the day. Winds from the North-Northeast will
diminish with lingering 20-25 knot gusts across the Cape and
Islands, and 15-20 knots farther north and west. Lingering clouds
and a north-northeast wind will slow down heating in Eastern Mass,
while the CT River Valley should mix to between 900 and 850 mb. For
the east, this means a mixing equivalent of 8-10C, supporting max
temps in the 70s. In western areas the mixing equivalent depends on
the depth...about 15-16C if mixing to 900 mb and 16-17C if reaching
850 mb. So temps there should reach at least the mid 80s and have
the potential of approaching 90.

Note that upstream the max temps yesterday reached the mid 90s in
Michigan.  Also note that record max temps for our area today are 90
to 96, so while a 90 in Worcester would tie a record, it would fall
short at the other sites.

Surf... Southeast swell of 4-5 feet lingers along the south and east
facing exposed coastlines today. High surf and dangerous rip
currents will be a concern. Swell is expected to diminish during the
afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Tonight...

Winds diminish tonight, which with clear skies will allow
temperatures to cool to dew point. We trended toward the mos values
for min temp, which was a couple of degrees lower than the standard
guidance. Radiation fog possible in the interior, and marine
fog/stratus is possible along the Cape/Islands/South Coast.

Sunday...

High pressure over the region Sunday. Heights at 500 mb are forecast
at or above 590 Dm, and 850 temps are forecast at 18-19C...the NAM
shows 20C. Average September values per ESRL are 578 Dm for 500 mb
heights and 10C for 850 mb temperature. So Sunday will trend toward
very warm daytime temperatures. Moisture profiles show limited
moisture around 850 mb and dry air below and above, so we expect a
sunny day. Full mixing to 850 mb would support high temps around 90
or the low 90s, while mixing that falls just short would reach the
mid to upper 80s. Light winds under the high pressure will allow
daytime sea breezes, which will keep temps cooler along the
shoreline.

We will go with upper 80s and around 90. This would be either near
or at record levels. Records are included in the Climate section
near the end of this discussion.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

Highlights...

* Summer warmth expected to the middle of next week
* Maria expected to sharply recurve out to sea southeast of New
  England late next week

H85 temperatures 17C to 19C and impressive upper level ridge with
H50 heights over 5850m support high temperatures well into the 80s
across much of the region Monday and Tuesday and possibly for some
of the region into Wednesday. A few interior spots may reach 90
degrees Monday, and perhaps even again Tuesday if the ECMWF 00Z. run
verifies. Sea breezes may temper max temperatures a little along the
coastal plain including Boston. Expansive outflow cloud shield from
Maria and slowly lowering mid level heights may lower temperatures a
few degrees on Wednesday but still above normal.

Model guidance brings a risk of showers to southern New England late
Wednesday. This is likely in response to a weakening cold front
ahead of an approaching broad upper trough with a band of K indices
above 30 with the 00Z operational GFS and ECMWF. This may provide
enough of a trigger for at least scattered showers. Will keep POPs
around 30 percent but any showers that do develop could have
efficient rainfall given warm rain processes at work and
precipitable water values near 2 inches.

The latter part of the week features an amplifying upper level
trough over the Great Lakes which would appear to provide the
impetus for Maria to make a sharp right turn and pass southeast of
New England. Model consensus keeps the track of Maria southeast of
the benchmark and max winds on the east side. There may be some
moisture entrainment into the approaching upper level trough so
Maria could contribute to some rain if this is not counteracted by a
band of subsidence outside of Maria`s circulation field. There is
some uncertainty as to how this may play out and so for now will
indicate chance POPs Thursday through Friday morning. Other impacts
associated with Maria will likely be high surf and dangerous rip
currents, mainly along ocean exposed south coast beaches. For
several days, Maria tracks near a great circle route in our
direction and hence will likely see significant long period swells
from the S or SE propagate into our coastal waters most of next week
with the subsequent result being high surf and rip currents. The
slow speed of Maria for the next several days may enhance the swell
activity during this period.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...

Today...Moderate confidence.

Lingering MVFR ceilings in Western and Central sections while
Eastern Mass and RI show IFR cigs and MVFR/IFR vsbys in fog and a
few early morning showers.  Drier air is moving in, so we expect
clearing skies and VFR conditions arriving from west to east during
the day. Low clouds may linger on Cape Cod and the Islands.  North
winds will diminish through the day, although some 20 knot gusts may
linger this morning along the Cape/Islands/South Coast.

Tonight...Moderate confidence.

Diminishing wind. VFR to start in most spots. Southeast Mass and RI
will trend to IFR/LIFR in fog and low clouds. Areas of fog will also
develop across the interior with IFR/LIFR conditions.

Sunday... High confidence.

Fog burns off during the morning. Most of the day will be VFR with
light winds. Sea breezes expected along the coastlines, including
BOS.

KBOS TAF...Moderate confidence. IFR cigs and potential 4SM vsbys in
low clouds and drizzle/fog early. Conditions should improve to VFR
late this morning with clearing during mid to late afternoon. North
to northeast winds will diminish through the day.

KBDL TAF...High confidence in TAF. Borderline MVFR/VFR cigs will
improve as clearing skies over the Berkshires sweep east this
morning. Areas of fog may develop 06Z-12Z tonight, although the
chance of this is stronger over valley locations north of
Springfield.

Outlook /Sunday Night through Wednesday/... Confidence...High.

Sunday night through Tuesday...VFR expected.
Tuesday night...Mostly VFR except MVFR in patchy stratus/fog some
interior valleys and near the south coast.
Wednesday...Generally VFR except MVFR ceilings/visibilities possible
in scattered late day showers and patchy late night/early morning
stratus/fog.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today... With the remnants of Jose well south of the waters and
moving slowly southeast, we expect conditions will improve over the
waters this weekend. Gusty north winds will diminish through the
day, with lingering 25-knot gusts this morning mainly on the
southern waters. Seas at 5 feet or higher on all exposed waters this
morning. These will subside, but with 5-6 foot heights lingering on
the outer waters through this evening.  Fog and drizzle this morning
with some poor vsbys, but this will diminish through the day.

A leftover 3 to 5 foot southeast swell will maintain high surf and
rip tide hazards at the coastline, diminishing late in the day.

Tonight...

Fog lingers along the southern and southeast coasts in the evening,
then moves to the coastline during the night. Expect periods of poor
vsbys, especially on the waters south and east of Cape Cod.  Winds
will diminish to less than 15 knots, but seas will linger at 5-6
feet on the southern outer waters.

Sunday...

High pressure building over the region will bring light wind Sunday,
with sea breezes developing at the shoreline. Poor vsbys in fog
early, but these will improve during the morning.  Seas of 5-6 feet
will linger oin the southern outer waters, and may work north into
RI Sound during the afternoon.

A south swell sent north from Maria will start showing itself in our
southern waters Sunday, with 3-4 feet swell heights in the
afternoon.

Outlook /Sunday Night through Wednesday/... Confidence...High

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

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

&&

.TIDES/COASTAL FLOODING...

Lingering high surf and additional beach erosion will still be
a concern today given high seas just offshore. These values are
diminishing.

Swells from Maria may increase the surf and associated rip current
risk across our ocean-exposed south coast starting late Sunday
and continuing through the week. This will be true even though
Maria may eventually recurve out to sea before getting too close
to New England.

&&

.CLIMATE...

Record High Max Temperatures for Today, Sunday, and Monday.

BOS  96/1895  90/1959  89/1926
ORH  90/1941  85/2010  85/1970
BDL  93/1941  89/1959  90/2007
PVD  92/1970  87/1959  89/1920

Extreme high values for dew points for each calendar day are
still in the low 70s, except for a couple of 68 and 69 values
at Worcester. These are unlikely to be realized.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 6 PM EDT this evening for MAZ007-019-
     020-022>024.
RI...High Surf Advisory until 6 PM EDT this evening for RIZ006>008.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for
     ANZ232>234.
     Small Craft Advisory until 4 PM EDT this afternoon for ANZ231-
     251.
     Small Craft Advisory until 10 AM EDT this morning for ANZ236.
     Small Craft Advisory until 11 PM EDT this evening for ANZ235-
     237-250.
     Small Craft Advisory until 6 PM EDT Sunday for ANZ254>256.

&&

$$

SYNOPSIS...WTB/RMT
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...RMT
AVIATION...WTB/RMT
MARINE...WTB/RMT
TIDES/COASTAL FLOODING...
CLIMATE...



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