Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 191104
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
704 AM EDT Tue Sep 19 2017

.SYNOPSIS...
Tropical Storm Warnings continue for coastal Rhode Island and
Southeastern Massachusetts as Hurricane Jose continues to move
north. Jose moves east-northeast Wednesday night before stalling
near Georges Bank Thursday through Saturday. This 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 PM THIS EVENING/...
**Tropical Storm Warnings continue for south coastal RI
 including Block Island, south coastal MA, Cape and Islands, and
 southeast coastal MA including Plymouth MA**

7 am Update...

Lots of clouds across Southern New England, with lingering fog
across Eastern Mass and RI...and Worcester.

Radar shows some bands of light showers coming up to the south
coast. Echoes are mostly light at this time.

No significant changes to the forecast.

Previous Discussion...

Jose remained a marginal hurricane at 2 AM EDT, and continue to
move slowly north. Expecting the outer rain bands to start
encroaching upon southern New England later this morning, and
especially this afternoon. These showers will be mainly across
southeast MA, diminishing in coverage heading west of the
Worcester hills.

Before this, areas of fog and plenty of clouds. Expecting
visibility to improve some this morning, as east to northeast
winds slowly increase. Below normal temperatures

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
19/00Z guidance has come into reasonable agreement regarding the
track of Jose. There are minor variations in timing and precise
track, but well within the margin of error for a hurricane
forecast. Have higher confidence in a track southeast of the
40N/70W benchmark. Used a consensus approach to smooth over
these minor differences.

Expecting Jose to weaken to a tropical storm tonight into
Wednesday. The eventual and gradual extratropical transition
(ET) process will allow the pressure gradient to strengthen
further out away from the storm center, with the radius of
maximum wind increasing with time.

Winds...

Based upon the current expected track, the most likely areas to
experience sustained tropical storm force winds will be the
Cape, Vineyard and especially Nantucket. Elsewhere across
southeast MA and RI, it is more likely to have frequent tropical
storm force gusts. A word of caution, it will not take much of a
northwest shift in track, closer to southern New England, to
place more of southeast MA and RI into higher sustained winds.
The strongest winds still appear to be late tonight into
Wednesday.

Given fully-leaved trees, there remains a risk for some tree
damage and power outages.

Rainfall...

With a slightly more offshore track, the heaviest rainfall axis
also shifts southeast. Much of southern New England now expected
to receive one inch of rain, or less. There should be a sharper
rainfall gradient across southeast MA and southern RI, with
total rainfall likely ramping up across the Cape and Islands.
Continuing the Flash Flood Watch for Nantucket and Cape Cod due
the combination of storm surge and the inability to fully drain
after each successive tide cycle.

High surf...

Long period southerly swell from Hurricane Jose will continue
to increase, resulting in high surf and dangerous rip currents.
Thereafter, swells will transition to more of a wind wave as
winds increase. High Surf Advisories will be issued for those
areas not currently covered with a Tropical Storm Warning.

For more information on the coastal flooding risk, see the
section below.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Big Picture...

Longwave upper pattern maintains ridge east/trough west. As in
previous model runs, the shortwave scale breaks this into two
smaller ridges with Jose in between. By Thursday the eastern
ridge is shifting southeast while the western ridge builds
northeast into the Great Lakes. This gives Jose an escape route
eastward, although only the GGEM shows the storm taking
advantage of this opportunity. The GFS and ECMWF hold the storm
over or just east of Georges Bank Thursday through Saturday.

The persistent ridge points to a warm period, especially
Saturday- Sunday-Monday.

Details...

Wednesday night through Monday...

High pressure building in from the west will bring clearing skies
and lower humidity. With Jose shifting east, expect the showers to
taper from west to east during Wednesday night and Thursday. The
pressure gradient is slower to move clear, which will mean north
winds at least 25 knots sustained and gusts around 40 knots
lingering on the Cape and Islands into Friday.

So clearing and drier weather will arrive soonest in Western New
England and advance through central and eastern sections Thursday
and Friday.  Dry all areas Saturday through Monday.

&&

.AVIATION /12Z 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/...

High confidence in trends. Lower confidence in timing.

Today and tonight...Influence from Jose begins to be felt.
Winds remain E-NE then shift more to the N early Wed morning.
Wind gusts increase to 40-50 kt during the overnight hours,
slowly increasing during the afternoon and evening, peaking
mainly on the Cape/Islands, but still 25-35 kt expected across
interior RI/SE MA and E CT. Rain/fog will lead to continued
lower vsbys, mainly MVFR but IFR also likely at times. Mainly
IFR CIGS except across extreme W MA, where some MVFR/VFR is
possible at times.

Wednesday...MVFR with areas of IFR in low clouds/rain/fog.
Northeast winds with potential for 35-40 kt speeds, gust around
60 kts possible near KACK. 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.

KBOS Terminal...High confidence in trends, lower confidence
in timing. Gusty winds begin later this morning, and especially
this afternoon.

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

Outlook /Wednesday Night through Saturday/...

Jose will slowly move east Wednesday night and 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 Wednesday night and Thursday with
gusts 25 to 45 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 Wednesday/...High confidence

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

Jose is the main driver of the winds and seas in the short term
period, and even into the outlook period.

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

Seas will continue to build across the southern New England
waters, which have already been impacted by large long period
swell. Very rough seas expected across all open waters with a
southern exposure, especially those south and east of the Cape
and Islands.

General east to east-northeast winds today continue to
slowly increase. The strongest winds should occur Wednesday,
with the greatest speeds on the coastal waters around the Cape
and Islands. Those are the waters most likely to experience
sustained tropical storm force winds.

Reduced vsbys in rain and areas of fog, especially tonight into
Wednesday.

Outlook /Wednesday Night through Saturday/...Moderate confidence.

Forecast track of Jose has shifted a little southeast with this
package, with the storm slowly moving off to the east Wednesday
night and Thursday. Jose will then linger offshore Friday and
Saturday. Tropical Storm force wind gusts may linger Wednesday
night and Thursday, 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 diminishing
Thursday and Friday, with lingering 5-6 foot seas on the outer
waters Saturday.

&&

.TIDES/COASTAL FLOODING...
Jose will affect the coastline in ways typical of a strong
nor`easter but with especially large swells coming into our south
coast. The slow movement of Jose will result in a long duration
event of tides above normal and erosion from tonight through
Thursday, and possibly still later.

For the ocean-exposed south coast from Westerly to Westport, we
anticipate the potential for moderate to severe erosion from
large swells that will be propagating into Block Island and
Rhode Island Sounds later today into Wednesday. There could be
areas of minor coastal flood from wave overtopping for the
Tuesday evening and Wednesday morning high tides.

For the rest of the Tropical Storm Warning area from Hull to
Plymouth, Cape Cod, Nantucket, and Martha`s Vineyard, we anticipate
generally minor to moderate coastal flooding for the Wednesday
midday, Wednesday night, and Thursday early afternoon high tides,
except there is a risk for high end moderate coastal flooding for
the Nantucket Harbor area for the Wednesday late night and Thursday
early afternoon high tides. We are anticipating a storm surge of
1 to 2 feet in these areas with 2 to 3 feet a plausible worst
case scenario for Nantucket.

We continue to forecast areas of severe beach erosion over multiple
high tide cycles for the outer Cape (mainly Eastham to Chatham, east
and south side of Nantucket, and south side of Martha`s Vineyard
where we may see waves near 20 feet and long periods enter the near
shore waters. A particular concern is the probable long duration
of this erosion event that may take its toll over multiple high
tide cycles. There is the risk that we will see some residual
erosion taking place through Friday and even possibly into the
weekend in a few spots.

For the coastline from Boston to Salisbury, we anticipate a low
risk risk of minor coastal flooding for the Wednesday midday
and Wednesday late night high tides. We may need to issue a
Coastal Flood Advisory for this stretch of coastline as we get a
little closer to the event.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Tropical Storm Warning for MAZ019>024.
     High Surf Advisory until 2 AM EDT Thursday for MAZ007.
     Flash Flood Watch from 6 PM EDT this evening through Wednesday
     afternoon for MAZ022-024.
RI...Tropical Storm Warning for RIZ006>008.
MARINE...Tropical Storm Warning for ANZ231>237-250-251-254>256.
     Small Craft Advisory from 11 AM this morning to 2 AM EDT
     Thursday for ANZ230.

&&

$$
SYNOPSIS...WTB/Belk
NEAR TERM...WTB/Belk
SHORT TERM...Belk
LONG TERM...WTB
AVIATION...WTB/Belk
MARINE...WTB/Belk
TIDES/COASTAL FLOODING...



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