Wednesday, September20, 2017 L-36.com


Marine Weather and Tides
Siasconset, MA

Version 3.4
What's New / NOTES
6/25/2017 - NOAA is having a major issue that impact the 7 day forecast load times. Many users are reporting problems. The issue has been reported.
5/23/2017 - Worked with NOAA again to speed up the 7 day forecast load times. Thanks to them for being responsive.
5/19/2016 - There were issues with the 3 day airport observation history. I switched to another data source. Let me know if you see any issues with the data feeds.

Sunrise 6:30AMSunset 6:46PM Wednesday September 20, 2017 3:34 AM EDT (07:34 UTC) Moonrise 6:39AMMoonset 7:12PM Illumination 0% Phase: New Moon; Moon at 29 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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ANZ005 301 Am Edt Wed Sep 20 2017
Synopsis for eastport me to stonington me out 25 nm.. Tropical storm jose will track se of cape cod today then begin turning back south on Thu. High pres will build down from the N Thu into Sat.

7 Day Forecast for Marine Location Near Siasconset, MA
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location: 38.84, -69.85     debug


Area Discussion for - Boston, MA
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Fxus61 kbox 200230
afdbox
area forecast discussion
national weather service taunton ma
1030 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
Bands of showers are sweeping in from the southeast with
additional bands in sight on radar south of nantucket. No change
in forecast logic since the evening with showers expected to
move through during the night.

Observed winds show gusts of 30 to 33 knots on the coastal
waters south of new england early at night. With jose moving
north-northeast we expect these winds to increase overnight with
tropical storm force winds reaching nantucket and parts of cape
cod by 12z.

Precipitable water values were 1.93 inches at chatham this
evening. The GFS brings 2+ inch precipitable water values by
12z, while the NAM lowers values to 1.5 inches. Tend to favor
the GFS scenario. This suggests showers along the CAPE and
islands trending to heavy downpours by morning.

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 02z 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 ...

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 these showers to
sweep across southern new england with reduced vsbys in locally
heavy downpours by morning.

Winds will increase during the overnight hours with a few gusts
reaching around 25 kt. Some early morning llws possible
cape island terminals as 2k ft winds approach 45 kt.

Wednesday and Wednesday night...

early am ifr gradually gives way to MVFR thenVFR 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 toVFR 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.

Tropical storm warnings continue on most of the coastal waters
with small crafts on boston harbor and mass bay, as well as
narragansett bay. Tropical storm force winds may reach the
southern waters toward morning.

Jose moves northeast well outside of nantucket Wednesday, but
will then stall near georges bank. This will allow the strong
winds to linger through Thursday.

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... Wtb doody
short term... Doody
long term... Correia
aviation... Wtb doody correia
marine... Doody correia
tides coastal flooding...



Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Nantucket, Nantucket Memorial Airport, MA168 mi41 minNE 145.00 miFog/Mist66°F66°F100%1008 hPa

Wind History from ACK (wind in knots)
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Last 24hrNE14NE15NE13NE14NE15
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1 day agoNE7SE5NE6NE5NE8E8NE10NE10NE10NE10NE10NE12NE12NE13NE10NE10NE9NE10NE10NE13NE13NE14NE14NE13
2 days agoCalmCalmCalmCalmCalmNE3N3N4S4E8E9SE8SE8SE5SE4E4E3E4E5E4E5NE3NE4E4

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The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerious of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.