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000
FXUS61 KBOX 172345
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
745 PM EDT Sun Sep 17 2017

.SYNOPSIS...
Weak high pressure will build across New England Monday as
Hurricane Jose lifts slowly north from the Mid Atlantic offshore
waters. Hurricane Jose will bring high surf and dangerous rip
currents through the middle of this week. Wind and rain effects
are likely, especially across Cape Cod and the islands Tuesday
into Wednesday. However, the full extent of these impacts and
their timing remains dependent on the storm track and intensity.
High pressure then builds over the region with drier and
seasonable weather Thursday through Sunday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

-- Changed Discussion --
730 PM Update...

Isolated showers in the CT River Valley region may last for
another hour or so, as SPC mesoanalysis page indicates around
500 J/kg of Cape. Since we are past sunset, showers should
continue to diminish, ending by 10 pm.

Other concern for tonight is the redevelopment of stratus and
fog across much of SNE. Fog bank along east coastal MA had
already moved into Boston. Fog will continue to spread across
east coastal MA and eventually into south coastal MA/RI this
evening. Areas of fog will eventually expand westward as
boundary layer cools with light onshore flow. A Dense Fog
Advisory has been issued for eastern MA and southern RI for
tonight. Lows mostly in the lower 60s.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Monday...

Stratus and fog will gradually lift and erode through the
morning into midday. However, expect more clouds to linger
through the day, especially eastern half SNE as low level
moisture is more plentiful with low level easterly flow
persisting.

Surface ridging from Maritimes high pres will extend across SNE
which should keep deeper moisture to the south. Expect a mostly
dry day although can`t rule out a few showers. Temps will be a
bit cooler than today given more cloud cover and some cooling in
the lower levels with persistent easterly flow. High mostly in
the 70s, possibly near 80 in the CT Valley.

Monday night...

As Jose slowly lifts north over the Mid Atlantic waters,
conditions will become more favorable for a possible PRE
overnight. Tropical moisture with PWATs nearing 2 inches will
be lifting north into the region with a possible low level
coastal boundary developing. Threat for showers will be
increasing overnight, especially in the coastal plain but
timing is still uncertain as models differ on timing. It is
possible the onset of the heavier rain holds off until Tuesday
so just chance chc PoPs for now. Increasing E/NE winds will be
developing along the south coast and especially the islands
late Mon night as northern periphery of the stronger low level
wind field approaches from the south.

High surf...

Long period southerly swell from Hurricane Jose will continue
to increase, peaking Monday evening with swell possibly reaching
10 ft over the southern waters resulting in rather high surf
and dangerous rip currents. Thereafter, swell will transition to
more of a wind wave as winds increase. High surf advisories
remain in effect for the southern beaches of Mass and RI.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
***Tropical Storm Watch posted for south coastal RI including
 Block Island, south coastal MA, Cape and Islands, and southeast
 coastal MA including Plymouth MA***

Tuesday thru Wednesday...Jose is in the spotlight.

For Tuesday morning models indicate we should at least be seeing
showers with brief heavy rainfall out ahead of the main rain bands
from Jose. It is challenging to pinpoint the location of a
Predecessor Rain Event, but the models have many of the ingredients
in place that indicate at least the potential for one during Tuesday
morning. H5 pattern is one ingredient that brings a favorable setup
for a PRE. Looking at H3, there is a weak but present jet max that
places us in the right rear quadrant. GFS and NAM indicate a leading
band of around 2" PWATs stretching into the southeastern
portion of our area, ahead of the bulk of moisture associated
with Jose. Also looking at potential for a weak leading short
wave. Will need to continue to monitor for possible heavier
rainfall potential Tue am. For this package have likely to
categorical pops for Tue am, then continue these higher pops
into Tue pm as rain bands more directly associated with Jose
likely move in.

The NHC forecast for Jose indicates Jose weakening to a Tropical
Storm as it makes its closest approach to our area. The forecast
track`s closest approach is centered near 40N/70W during Wed
morning, which is consistent with much of the model guidance.
However there is still ample uncertainty on the exact track, as the
5 year average error of a hurricane track forecast 48 to 72 hours in
advance is about 75-100 nautical miles either side of the forecast
track. For example, Nantucket is only about 85 miles north of the
40N/70W benchmark, well within the margin of error.

12Z GFS/GEFS: GFS Brings Jose over and somewhat inside 40N/70W,
slightly closer to ACK than 06Z run. Making its closest approach
to SNE around daybreak Wed. GEFS Ensemble mean has Jose
centered on 40N/70W at 12Z Wed, then pulling east at least for a
period of time. 12Z UKMET is similar in timing of closest
approach followed by movement to the E on Wed.

Guidance that brings Jose closer or has a longer residence time near
our area include the NAM and CMC. NAM brings Jose`s center over the
Cape and Islands during Wed. CMC slower with the track, though still
offshore. 12Z ECMWF continues to have a northerly approach until 18Z
Wed, then like its 00Z counterpart stalls out the system, allowing
it to meander.

What does this all mean? There is still uncertainty on the exact
track of Jose, and a slight change in track has the potential to
make a big difference in winds and rainfall on land. Stay tuned for
further updates from NHC and NWS Taunton.

Likely to categorical pops continue thru Tuesday night, diminishing
gradually during Wed. Utilized GFS instability parameters to assess
t-storm potential, with LIs around zero across the eastern portion
of the area Tue-Tue night, and somewhat less t-storm potential
across the interior.

Rainfall totals from WPC bring 3-5 inches of rainfall to the far
southeastern portion of our area, highest totals on the Cape and
Islands. This rainfall will have the potential to produce
substantial urban and poor drainage flooding. Rivers and streams
in southeast MA and RI are running predominantly below normal,
some on the low end of normal. So there is a degree of buffer on
area waterways. Can`t rule out a small stream getting close to
bankfull if rainfall falls in short enough period of time.

Thursday thru Sunday...

Once Jose finally departs our region, we should receive a period of
more tranquil weather late this week into next weekend. Can`t
completely rule out some lingering showers during Thu in
southeastern portions of the area, depending on the ultimate path of
Jose.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

High confidence in trends. Lower confidence in timing.

Tonight and Monday...Widespread IFR/LIFR developing tonight as
stratus and fog spreads inland. Exact timing uncertain.
Conditions gradually improve by late Mon morning and becoming
VFR in the afternoon. But MVFR cigs may linger in the east. Low
risk of a shower Monday near the coast.

Monday night...IFR/LIFR stratus and fog redeveloping. Increasing
risk of showers, especially after midnight in the coastal plain.
E/NE gusts to 25 kt developing over the islands toward daybreak.

KBOS Terminal...High confidence in trends. Lower confidence in
timing. IFR/LIFR stratus and fog remains overnight, conditions
improving to MVFR around midday Monday.

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

Outlook /Tuesday through Friday/...

Tuesday-Wednesday...Moderate confidence.

MVFR with areas of IFR in low clouds/rain/fog. Northeast winds
with potential for 35-40 kt speeds, gust around 50 kts possible
ACK. Poor visibility on Cape and Islands in rain and fog.
Conditions are dependent on the track and speed of Hurricane
Jose. Some improvement possible from west to east Wednesday
afternoon.

Thursday and Friday...Moderate confidence.

Early morning MVFR/IFR cigs/vsbys in patchy early morning fog,
then mainly VFR.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Through Monday...Light easterly flow gradually increasing during
Mon afternoon but below SCA. Increasing long period south swell
will result in seas building to 5-7 ft over the southern
waters. Poor vsbys in areas of dense fog at times.

Monday night...E/NE winds gradually increase with gusts 25-30
kt over southern waters by daybreak. Swell peaks in the evening
then transitioning to more wind wave. Seas building to 10-15 ft
outer southern waters. Poor vsbys in fog. Increasing risk of
showers after midnight.

Outlook /Tuesday through Friday/...Moderate confidence.

***Tropical Storm Watch posted for much of the southern New
 England coastal waters***

Seas will continue to build Tuesday and Tuesday night in
advance of Jose. Tropical Storm Watch headlines have been posted
for much of the coastal waters, with the exceptions of Boston
Harbor and Mass Bay/Ipswich Bay. Please refer to the latest
Marine Weather Message /BOSMWWBOX/ for details.

Seas on the southern outer coastal waters could potentially
build to 15-25 feet, with seas 10-20 feet possible in RI/BI
Sounds. High seas will spread to the eastern coast of
Massachusetts, especially Outer Cape Cod Tuesday and Wednesday.
Seas will subside Wednesday night. Seas of 5 to 10 feet may
linger on the outer coastal waters during Thursday and Friday.

Final impacts will depend on the track of Jose, which still has
time to change over the next couple of days. Mariners are
strongly urged to monitor the latest forecasts regarding Jose.

&&

.TIDES/COASTAL FLOODING...
Jose`s large wind envelope will likely produce significant seas
with a large swell component moving onshore early to mid next
week. Significant wave action should occur on top of relatively
high astronomical high tides and a building surge. As a result,
we believe there is a high risk of moderate to severe beach
erosion over a prolonged period early next week. Multiple high
tide cycles of large swells breaking onshore have us concerned
that we could experience a very serious beach erosion event
along portions of both our south and east facing ocean- exposed
shorelines next week.

In addition and dependent upon how close Jose gets to our
coast, there is also a risk for minor to moderate coastal
flooding along portions of the coast with probably southeast and
east facing shorelines most at risk.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...None.
MA...Dense Fog Advisory until 3 AM EDT Monday for MAZ005>007-
     013>024.
     High Surf Advisory until 8 PM EDT Monday for MAZ020-023-024.
     Tropical Storm Watch for MAZ019>024.
RI...Dense Fog Advisory until 3 AM EDT Monday for RIZ002-004>008.
     High Surf Advisory until 8 PM EDT Monday for RIZ006>008.
     Tropical Storm Watch for RIZ006>008.
MARINE...Tropical Storm Watch for ANZ231>237-250-254>256.
-- End Changed Discussion --
&&

$$
SYNOPSIS...KJC/NMB
NEAR TERM...KJC
SHORT TERM...KJC/NMB
LONG TERM...NMB
AVIATION...KJC/NMB
MARINE...KJC/NMB
TIDES/COASTAL FLOODING...Staff