Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 192331
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
731 PM EDT Tue Sep 19 2017

.SYNOPSIS...
Although some Tropical Storm Warnings will be dropped Jose
moves east- northeast late tonight before stalling near Georges
Bank Thursday through Saturday. Tropical Storm Warnings continue
for Cape Cod and Nantucket and surrounding waters. With Jose
stalling, it may be close enough to maintain wind for a couple
of days on Cape Cod and Islands. High pressure builds in from
the west with dry weather for Thursday to Saturday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
730PM update...
On and off banded SHRA continue across mainly the S tier of S
New England. Guidance continues to support this lifting N with a
plume of moisture through the remainder of the evening hours,
along with a few heavier elements thanks to a modest burst of
lift coincident with a weak vort-max passage. POPs will be
adjusted to better match current timing but otherwise the
forecast remains on track. Still not enough to support a dense
fog advisory yet given that pres gradient should remain elevated
enough to mitigate fog development outside of onshore advective
fog. Something to watch.

Previous discussion follows...

Hurricane Jose, currently about 285 miles S of Nantucket
continues a mainly N track toward S New England this afternoon.
Latest Advisory from NHC suggests the E turn begins this
evening, with the final track carrying it S of the 40/70
benchmark, a very gradual S and E trend through tomorrow night
which has been hinted at in guidance/advisories over the past 48
hours or so. For more on direct impacts from Jose, see the
short term section below.

Focusing on the near term, will monitor the increasing of winds
through the overnight hours such that at the very least,
tropical storm magnitude gusts should be reaching Nantucket and
possibly portions of Cape Cod by 12Z. Elsewhere, wind gusts will
be increasing as well thanks to gradual enhancement of the sfc
gradient and H92 LLJ along the NW quad shifting N. Gusts mainly,
20-30 kt away from the immediate wind radii of Jose.

Otherwise, initially moisture plume N of Jose allows PWATs to
reach +2.00 inches overnight coincident with a modest burst of
instability and mid lvl lift associated with the weak shortwave
progged to assist with the E shift in Jose. Latest mesoscale
guidance, and to a lesser extent the more coarse operational
guidance is showing that the current modest bands of SHRA which
continues to slowly shift inland could actually intensify
overnight, leading to periodic heavy downpours to be embedded
with this band. WRF QPF is likely too high however as it is
nearly stationary with this band, while the actual progression
looks to be transitory S-N lifting as the bands occur. The
primary issue would be if a heavier SHRA is able to impact an
urban area for urban flooding. Something to watch.

Otherwise, not expecting as widespread dense fog as previous
nights in spite of the increase in overall column moisture.
Rising moisture aloft will limit drizzle and fog development
somewhat and the increasing pres gradient suggested in the mass
fields should promote more mixing than previous nights. Still
something to watch, but not confident enough to hoist and dense
fog headlines with this update.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY/...
** Tropical Storm Warnings Continue For Cape Cod, Nantucket and
 the surrounding Waters **

As Jose begins its shift to the E late tonight it is expected to
begin to slow its forward progress and make its slow, closest
pass just S of the 40/70 benchmark through the day tomorrow.
Given the gradual shift to the SE mentioned above, the
expectation for true 34 kt (39 mph) sustained wind over land is
looking less likely, so tropical storm warnings will be dropped
for RI and SE coastal MA except for Cape Cod and Nantucket,
where this risk continues. Jose then is likely to stall, with
lingering impacts holding into the daytime on Thu.

Winds...
Gradual increase begins overnight tonight, but is unlikely to
peak until after sunrise in the morning. Strongest sustained
winds/gusts across the extremities of Cape Cod and Nantucket
linger through much of the day as Jose makes its closest pass,
reaching 40-50 mph with a few gusts higher. Further inland,
especially for SE MA and RI, inclusive the I-95 corridor between
Providence and Boston, gusts may approach tropical storm
magnitude, but are generally at or below wind advisory
thresholds, 35-45 mph gusts. Given fully foliated trees, the
continued stress from these gusts could still lead to scattered
tree damage and power outages which may require the issuance of
a wind advisory.

Winds on Thu are interesting because even as Jose shifts just to
the SE, and further offshore, the continued extratropical
transition process is likely to broaden the wind radii, and
guidance supports this with a strong H92 jet (40-50 kt) across
its NW quadrant. With the primary moisture plume shifting E,
this could allow for better sfc mixing, supported by an increase
in 1000-925hPa lapse rates. Therefore, it`s possible the
strongest gusts over the interior coastal plain actually occur
on Thursday, exacerbating the wind stress, and likely requiring
another wind headline.

Rainfall...
Aside from rainfall already haven fallen (mainly a quarter inch
or less) and rainfall expected overnight from the enhanced SHRA
activity expected away from the core of Jose, as we transition
into tomorrow, the focus will shift back towards bands directly
associated with Jose. Therefore, a transition just to SHRA
inland with more widespread, stratiform mod-hvy rain is expected
mainly toward SE MA. Guidance still a bit uncertain on the peak
axis through the day tomorrow and tomorrow night, some over or
just offshore of Nantucket and the outer arm of Cape Cod. Given
this uncertainty, will maintain the current Flash Flood Watch as
these areas have the highest risk for the axis of heavy rain to
pass over. Generally 3-5 inches possible, with a low risk for
higher amounts for Cape/Nantucket, dropping back to between 1-3
inches for E RI and portions of the coastal plain, while areas
of interior MA/RI and CT are likely to see under an inch
inclusive of the rain expected tonight. Note that the gradient
of heaviest rain is likely to continue to be refined and will
likely tightened once the trajectory of Jose`s outer bands are
better realized.

High surf...
A building offshore swell, combined with gusty NE winds will
lead to high surf along almost all area beaches and coastlines
tonight into Thursday save for Boston Harbor, which is well
sheltered from this setup. Seas offshore could reach as high as
25-30 ft well to the SE of Nantucket and long periods of 12-14
seconds. This will lead to high energy waves and a risk for
dangerous rip currents. We will be hoisting high surf advisories
where Tropical Storm Warnings are dropped. Swells begin to
linger Thu, but are likely to remain elevated enough to support
the continuation of high surf headlines.

For more information on the surge/coastal flooding/erosion
potential, see that section below.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
With a tilted axis of high pressure building over the Great Lakes
Friday, Jose will be pushed southwest but ultimately remain
southeast of Nantucket.

Dry conditions will return to the region through early next week.
However, Tropical Storm Force winds could continue across the
Cape and Islands through Friday. Winds will be slow to diminish
as Jose remains to our south.

A persistent ridge points to a warm period, especially Friday
through Monday.

Details...

Thursday night through Tuesday...

Tropical Storm Jose will be approximately 300 miles southeast of
Nantucket Thursday evening.

Both the ECMWF and the GFS are in agreement on the position of Jose
through Monday morning. Jose will essentially sit at 40 N
through 12z Monday, but depending on the position of the high
pressure and shear aloft, Jose may considerably weaken and
therefore have very minimal impact on the region.

High pressure builds in from the west Friday, bringing clearing
skies and lower humidity.

Unfortunately, with Jose remaining in close proximity, an
extended wind field will continue through Friday. The Cape and
Islands will see gusts surpassing 40 knots well into Saturday.

Models are not in agreement when it comes to Jose on Day 6. The
ECMWF model take Jose further southwest as a high builds to its
north. By Monday, Jose makes landfall at the Delmarva Peninsula. The
GFS however has Jose turning back northeast towards Nova Scotia on
Saturday and further out to see by Monday.

Temperatures through the weekend will be well above normal with
highs forecast to be in the mid 80s. The normal high for this time
of year is 70 degrees.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...

High confidence in trends. Lower confidence in timing.

Tonight...
On and off banded SHRA continue across mainly the S tier of S
New England. Guidance continues to support this lifting N with a
plume of moisture through the remainder of the evening hours,
along with a few heavier elements thanks to a modest burst of
lift coincident with a weak vort-max passage. POPs will be
adjusted to better match current timing but otherwise the
forecast remains on track. Still not enough to support a dense
fog advisory yet given that pres gradient should remain elevated
enough to mitigate fog development outside of onshore advective
fog. Something to watch.

Otherwise, winds begin to increase during the overnight hours
with a few gusts reaching around 25 kt. Some early morning LLWS
possible Cape/Island terminals as 2kft winds approach 45 kt.

Tomorrow and tomorrow night...
Early AM IFR gradually gives way to MVFR then VFR mainly W of
the Worcester hills. Otherwise mainly IFR or low end MVFR CIGS
and vsbys remain in place across E MA and RI. SE MA/Cape/Islands
experience on and off heavy RA as Jose makes its closest pass.
Winds gust to 35-40 kt mainly Cape/Islands with lower gusts
inland.  LLWS possible as well, mainly SE MA.

Thu...
Gradual improvement as low clouds and rainfall pull further to
the E with time. Winds out of the NE continue, gusts to 30-40 kt
at times possible even across inland SE MA and RI especially
with any breaks of sun.

KBOS Terminal...High confidence in trends, lower confidence
in timing. Winds gradually increase through the overnight, but
gusts should generally remain below 30 kt.

KBDL Terminal...High confidence in trends. Lower confidence in
timing.

Outlook /Thursday Night through Sunday/...

Jose will slowly move east Thursday. Lingering MVFR cigs and
vsbys in central and eastern Mass will improve to VFR Thursday.
VFR conditions likely Friday and Saturday.

Strong winds from the north continue Thursday with gusts 25 to
40 knots, strongest over Cape Cod and Islands. These will
diminish Friday.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...High confidence

***Tropical Storm Warnings Continue For Waters except those
 surrounding Cape Cod and the Islands.***

Jose remains the dominant driver for marine weather into Thu.

Given the slight SE shift in track over the last 24 hours or so,
some of the Tropical Storm Warnings will be dropped with this
forecast update given sustained winds of 34 kt are looking less
likely. The Tropical Storm Warnings will however continue for
the waters across mainly S of Rhode Island immediate
surrounding the Cape/Islands.

Even in the areas where Warnings have been dropped, wind gusts
could still exceed Tropical Storm magnitude beginning during
the early morning hours tomorrow, and lingering into at least
Thu as Jose or the remnants thereof stall to the SE.

Building swells have already reached as high as 16 ft this
afternoon at buoy 44008 SE of Nantucket and will continue to
increase, especially over the waters with a southern exposure
into tomorrow and tomorrow night. N-NE winds may help to
mitigate the swell somewhat, but very rough conditions are
expected to linger at least into Thu before beginning to slowly
subside.

Otherwise, reduced vsbys in rain and areas of fog, especially
tonight into tomorrow night.

Outlook /Thursday Night through Sunday/...Moderate confidence.

Forecast track of Jose shifted a little southeast. Jose will
then linger offshore Friday and Saturday. Tropical Storm force
wind gusts may linger through Thursday night at least, mostly
on the waters around Cape Cod and the Islands. Winds will
continue to diminish Friday and Saturday.

Seas remain very rough Wednesday night with seas up to 20 feet on
parts of the outer waters. The seas will then slowly diminish
Thursday and Friday, with lingering 5-6 foot seas on the outer
waters Saturday.

&&

.TIDES/COASTAL FLOODING...
We anticipate the greatest impact to be along the Nantucket, Cape
Cod, and Martha`s Vineyard shorelines where Tropical Storm Warnings
remain in place. A long duration of large waves pounding the shore
with elevated water levels is expected to yield areas of severe
erosion along the Nantucket east and south shore, south side of
Martha`s Vineyard, and the ocean coast of the outer Cape from
Eastham to Orleans to Chatham. The erosion may persist into at least
Friday. A storm surge of 2 to 3 feet will likely result in minor to
moderate coastal flooding for the Nantucket Harbor area, mainly for
the Wednesday night, Thursday, and Thursday night high tides.

Relatively strong northerly winds may result in minor coastal
flooding and areas of moderate erosion along the north side of Cape
Cod or Cape Cod Bay side for the Thursday and Thursday night high
tides.

Across the ocean exposed south coast of Rhode Island and Westport in
Massachusetts, a persistent swell is expected to result in fairly
significant erosion also over a multi-day span.  We note that seas
of 16 feet had reached Nantucket Shoals buoy by 3 PM.

Along the Plymouth County coast from Hull to Plymouth, we anticipate
pockets of minor coastal flooding for the Wednesday midday high tide
and perhaps a few more numerous areas of minor coastal flooding for
the Wednesday night and Thursday early afternoon high tides.
Incoming waves of possibly as high as 15 feet may build across Mass
Bay by late Wednesday. At this time we think the impacts will be
more in the nuisance range. We will be issuing a Coastal Flood
Advisory for this stretch of coastline, since it falls outside the
Tropical Storm Warning. For Boston northward, only isolated pockets
of coastal flooding are anticipated and not widespread enough to
warrant an advisory at this time.

Outside of the Tropical Storm Warning area, we will have High Surf
Advisories that will include the Essex and Plymouth County coasts in
eastern Massachusetts and along the Rhode Island ocean exposed coast
to the Westport area in Massachusetts.  The High Surf Advisory
extends through Thursday night but may need to be extended through
the day on Friday due to the persistent NNE flow.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Tropical Storm Warning for MAZ022>024.
     High Surf Advisory until 8 AM EDT Friday for MAZ007-019-020.
     Coastal Flood Advisory from 11 AM Wednesday to 3 PM EDT
     Thursday for MAZ019.
     Wind Advisory from 10 AM Wednesday to 6 PM EDT Thursday for
     MAZ006-007-013>021.
     Flash Flood Watch through Wednesday afternoon for MAZ022-024.
RI...Tropical Storm Warning for RIZ008.
     High Surf Advisory until 8 AM EDT Friday for RIZ006-007.
     Wind Advisory from 10 AM Wednesday to 6 PM EDT Thursday for
     RIZ002>007.
MARINE...Tropical Storm Warning for ANZ231>235-237-250-254>256.
     Small Craft Advisory until 6 PM EDT Thursday for ANZ230-236-
     251.

&&

$$
SYNOPSIS...Doody/Correia/Thompson
NEAR TERM...Doody
SHORT TERM...Doody
LONG TERM...Correia
AVIATION...Doody/Correia
MARINE...Doody/Correia
TIDES/COASTAL FLOODING...



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