Area Forecast Discussion
Issued by NWS Boston, MA

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448
FXUS61 KBOX 201408
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1008 AM EDT Wed Sep 20 2017

.SYNOPSIS...
Jose moves northeast today, then turns east and circles well
southeast of Nantucket tonight through Saturday. This may be close
enough to maintain rain and strong wind for a couple of days over
Southeast Mass, favoring Cape Cod and Islands as well as the
adjacent ocean waters. High pressure builds in from the Great
Lakes with dry weather early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
10 am update...
Weak convergence within a deep moisture plume continues to lead
to isolated SHRA and DZ across portions of E MA/RI this morning,
meanwhile the first in a series of direct rain bands from Jose
shifts over Nantucket and the outer arm of Cape Cod. While
guidance is still struggling with both of these features, will
maintain the current QPF until better agreement between guidance
is shown.

Otherwise, forecast is on track for the most part.

Previous discussion...

Tropical Storm Jose has turned northeast. The center will pass well
south and east of the 40N/70W benchmark today, slowing to a crawl
tonight.

Winds will increase today, especially along and southeast of the I-
95 corridor, with the strongest winds on Cape Cod and the Islands.
Speeds may reach Tropical Storm force on the Cape and Islands this
afternoon and evening. Data shows some low level mixing, with 30 to
35 knot winds in the layer. So we expect 30 to 35 knot gusts inland
and 35 to 40 knot gusts in Eastern Mass and parts of RI.

Rainfall has the potential to generate heavy downpours, especially
in Southeast Mass and RI. PW values are forecast to climb to around
2 inches, signaling a large amount of moisture available to
precipitate. Flash Flood Watch continues today across Cape and
Islands.

Offshore swell directed shoreward by Jose will maintain high surf to
the South Coast, while a persistent northeast wind will drive
water to shore from the Gulf of Maine. We are maintaining high
surf advisories along the shoreline that is not covered by
Tropical headlines.

Lower chance of showers in the CT Valley and other western areas.
Even so, the cloud shield is extensive enough to bring mainly cloudy
skies. We stayed close to guidance values for the max temps.

&&

.SHORT TERM /THURSDAY/...
Jose drifts offshore south and east of the benchmark. This will
be close enough to maintain the moist airmass and bring
lingering showers tonight and possibly Thursday. Total rainfall
has a potential of up to 3-5 inches on the Cape and Islands,
and less than an inch North and West of I-95. We will maintain
the Flash Flood Watch for the Cape and Islands.

Winds similar to today will linger through Thursday before
diminishing. Heavy surf and dangerous rip currents will also
continue through Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Highlights...
 * Gusty winds persist on Cape Cod and Islands Friday
 * Dry and seasonable over weekend and early next week
 * Monitor NHC forecasts as Maria heads through Caribbean

Medium range ensembles favor large scale pattern which features
building upper ridge from southern Plains to Great Lakes as mean
trough develops over western states. This will force Tropical
Storm Jose back to the south and southwest through weekend while
slowly decaying, favoring dry and warmer conditions in southern
New England as winds on Cape/Islands subside.

This pattern should remain in place for most of next week, which
has implications on track of Hurricane Maria. Latest NHC/WPC
guidance brings Maria northward but off East Coast, similar to
Jose, as upper ridge remains to our west. At this point Maria
bears watching, as we typically advise with tropical systems
approaching Bahamas, but for now we expect dry weather early
next week. That said, we could see increasing winds and building
swells again near South Coast by Tue or Wed.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...

Today...

Ceilings below 1000 feet from Worcester east, and 1000-2500 feet to
the west. Vsbys are generally 3-5 miles in Eastern Mass and 1-3
miles on Cape Cod and Islands due to rain and fog. Expect these low
conditions will continue through the day. Low level wind shear will
be generated by Tropical Storm Jose offshore with 2000 foot winds 50-
60 knots across the Cape and Islands.

Tonight...

Expect low cigs and vsbys to continue tonight in Eastern Mass, while
conditions improve to VFR in the west.

Thursday...

Gradual improvement in ceilings from west to east with areas off-
Cape becoming VFR by afternoon. Lingering MVFR cigs over Cape Cod
and Islands.  North-northeast winds continue to gust near 20 knots
in the west, 20-30 knots in the central hills, and 30-40 knots in RI
and Eastern Mass.

KBOS TAF...High confidence in TAF trends, lower confidence in
timing. Sustained NNE winds around 20 knots, and gusts increasing to
20-30 knots.

KBDL TAF...High confidence in TAF trends, lower confidence in
timing.

Outlook /Thursday Night through Sunday/...

High confidence.

Thu night and Fri...Lingering MVFR ceilings in eastern MA,
otherwise VFR. N winds gusting to 25-35kt on Cape Cod/Islands.

Sat and Sun...VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Thursday/...

Tropical Storm Jose passes southeast of the waters today, then
lingers well offshore through at least Thursday. This will allow
strong winds to linger over the waters through at least Thursday,
with gusts of 35-45 knots over most of the waters, with gusts 25-30
knots on Narragansett Bay and Mass Bay/Boston Harbor.

Building swells have already reached as high as 16 ft at buoy 44008
SE of Nantucket. Expect high swell will continue through
Thursday, especially over the waters with a southern exposure.

Showers and fog will also linger through Thursday, creating poor
vsbys.

Outlook /Thursday Night through Sunday/...

Moderate confidence.

N winds remain strong through Saturday morning, with gusts of
35-40kt on south coastal waters as Jose drifts S and away from
southern New England. Winds diminish further as high pressure
builds over region this weekend, but seas will take most of
weekend to subside on open south coastal waters.

&&

.TIDES/COASTAL FLOODING...
Main concern is for severe beach erosion along Nantucket`s south
and east shores, south shore of Martha`s Vineyard, and ocean-
facing shore of outer Cape, due to long duration of large waves
pounding the shore, which may persist into Friday.

Storm surge of around 2 ft on Nantucket late tonight and Thursday
should bring minor to perhaps moderate coastal flooding to
Nantucket Harbor. Minor coastal flooding is expected on
Martha`s Vineyard with a storm surge of 1 to 2 ft, and also
along eastern MA coastline with less of a storm surge but
compensated by wave action with seas around 15 ft offshore.
North facing shore of Cape Cod (Bay Side, including Sandwich)
may see minor coastal flooding Thursday and Thursday night as a
result of strong northerly winds.

For RI South Coast, only splashover is expected at worst with
storm surge of around 1 ft.

Tropical Storm Warnings cover minor coastal flooding and high
surf for Cape Cod and Islands. Elsewhere, we will maintain
Coastal Flood Advisory for Plymouth County coastline where minor
coastal flooding should be more prevalent, and will keep High
Surf Advisory posted for entire E MA coastline.

&&

.EQUIPMENT...
KBOX WSR-88D Z-R relationship has been changed to Tropical to
get better rainfall estimates than with Convective. 00z CHH
sounding showed precipitable water of 1.93" along with deep
saturated above-freezing layer (10KFT warm cloud depth) which
is supportive of warm rain processes.

&&

.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 until 3 PM EDT Thursday for MAZ019.
     Wind Advisory until 6 PM EDT Thursday for MAZ006-007-013>021.
     Flash Flood Watch through Thursday morning for MAZ022-024.
RI...Tropical Storm Warning for RIZ008.
     High Surf Advisory until 8 AM EDT Friday for RIZ006-007.
     Wind Advisory until 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...WTB/JWD
NEAR TERM...WTB/Doody
SHORT TERM...WTB
LONG TERM...JWD
AVIATION...WTB/JWD
MARINE...WTB/JWD
TIDES/COASTAL FLOODING...
EQUIPMENT...



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