Tuesday, December18, 2018 L-36.com


Marine Weather and Tides
Siasconset, MA

Version 3.4
What's New / NOTES
10/6/2018 Colors of tide XTide graphs changed to emphasize that they were upgraded. See next note. Comments welcome.
10/4/2018 I have fixed XTide and updated the harmonic files. There were some name changes so you might have to click EDIT to find the new station name.

Sunrise 7:05AMSunset 4:19PM Tuesday December 18, 2018 1:49 PM EST (18:49 UTC) Moonrise 2:41PMMoonset 3:05AM Illumination 85% Phase: Waxing Gibbous; Moon at 11 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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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 181735
afdbox
area forecast discussion
national weather service boston norton ma
1235 pm est Tue dec 18 2018

Synopsis
Expect windy and cold conditions today. High pressure will
bring dry conditions for mid week, with a moderating
temperature trend peaking on Friday. Strong low pressure will
pass west of the region Thursday night into early next weekend,
bringing rain that will fall heavily at times especially during
Friday. Colder temperatures then return early next week.

Near term until 6 pm this evening
1015 am update...

gusty northwest winds continue this morning... Recent
observations have been near or below wind advisory criteria and
are expected to decrease slowly through the day. For this reason
the wind advisory has been shortened, ending at 11 am. Winds,
though, will remain elevated through the afternoon. As expected
a few mid-high clouds traverse the eastern ma coast as the
shortwave rotates through... These should be brief and scattered
in nature.

645 am update...

upper low pressure south of nova scotia. A shortwave in the flow
around the low sweeps across eastern mass this morning and then
moves out to sea.

11z pressure change chart shows the core of pressure rises
directly over SRN new england. Expect this to move offshore
during the morning, at which point pressures rise more slowly
and the pressure gradient relaxes... Therefore, less wind.

Observed winds along the coast have been borderline for a wind
advisory, but close enough to keep the advisory in place
through the morning.

Mixing to about 925 mb, with temps at that level around -8c.

That suggests high temps either side of freezing. So the current
forecast looks fine at this time.

Short term 6 pm this evening through 6 pm Wednesday
High pressure will be our dominant weather feature tonight into
Wednesday. Winds will continue to diminish through this period,
and be more from the W than nw. Dry weather expected through
this period.

Very cold conditions tonight, with low temperatures in the
single digits above zero and teens common away from the
immediate coast. With some sunshine Wednesday and warm air
advection beginning, high temperatures recover some, but will
remain below normal.

Long term Wednesday night through Monday
Big picture...

Thursday shows ridges over the western atlantic and the rockies,
while a deep trough digs over the mississippi valley. Closed low in
the base of the deep trough will sweep up the east coast Friday and
across new england Saturday. The flow over the usa then becomes more
zonal, with an embedded shortwave moving through early in the week.

Mass field show good agreement through Friday and possibly Saturday.

Mslp fields show the surface low taking an inside track through
ny pa Friday. All show the zonal upper flow Sunday-Monday, but with
different timing for the movement of the shortwave. Thermal fields
are similar through Friday with h850 temperatures in the mid teens
briefly moving up across our area Friday.

Concerns...

Thursday-Friday...

as noted, the midwest deep trough ejects up the eastern usa Thursday
night and Friday, crossing new england Saturday. The atlantic high
should keep enough low level dry air to keep the weather dry during
the day Thursday.

Deep moisture moves in Thursday night with pw values forecast to 1
inch all the way to the white mtns while values of 1.5 inches reach
the south coast. As per the SPC sounding climatology, even the 1
inch values are at the upper end of what is expected in mid
december while 1.5 inches would be at or near record levels.

South to southeast flow builds Thursday night with 65 to 85 knot
winds forecast at 850 mb and winds near 35 knot forecast at 1000 mb.

The former actually suggests surface winds could gust to 45 knots.

Bufkit soundings show abv freezing air to at least 800 mb. Based on
this and the expected storm track through new york, expect southern
new england will have rain developing Thursday night, especially
after midnight, and continuing through Friday. Rainfall should total
at least 1-2 inches with potential for some higher amounts.

Potential for winds at advisory levels, especially in
eastern central mass and ri.

Rest of the period...

dry. Height contours at 500 mb are forecast above normal Wednesday
night through Saturday, then seasonable or a little below on Sunday
and Monday. This would mean above normal temperatures late this
week, trending to seasonably cold temps early next week.

Aviation 18z Tuesday through Sunday
Forecaster confidence levels...

low - less than 30 percent.

Moderate - 30 to 60 percent.

High - greater than 60 percent.

Short term through Wednesday ... High confidence.

Today... VFR. Windy with gusts to 25-30 kts out of the nw.

Tonight... VFR. NW wind gusts 20-25 kt early, diminishing to
less than 20 kt by midnight.

Wednesday...VFR. Light W SW winds.

Kbos terminal... High confidence in taf.

Kbdl terminal... High confidence in taf.

Outlook Wednesday night through Saturday ...

Wednesday night through Thursday:VFR.

Thursday night: mainly MVFR. Breezy. Ra.

Friday: mainly ifr, with areas MVFR possible. Windy with gusts
to 35 kt. Ra, patchy br.

Friday night: mainly ifr, with areas MVFR possible. Windy with
local gusts to 30 kt. Ra, patchy br.

Saturday: mainly MVFR, with local ifr possible. Windy with
local gusts to 30 kt. Chance ra.

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.

Buoy reports and some of the airport observations on the cape
and islands all show NW winds gusting to gale or near-gale
levels. This should continue through the morning, then subside
this afternoon. The winds will maintain rough seas, which will
take longer to subside across the eastern and southern outer
coastal waters of ma and ri. Seas continue to subside Wednesday.

Significantly colder air will move across the waters today into
tonight. With the gusty winds and rough seas, areas of light
freezing spray are likely along the nearshore waters of the ma
coast into this evening.

Outlook Wednesday night through Saturday ...

Wednesday night through Thursday: winds less than 25 kt.

Thursday night: low risk for small craft advisory winds with
gusts up to 30 kt. Rain.

Friday: low risk for gale force winds with gusts up to 35 kt.

Areas of rough seas. Rain.

Friday night: moderate risk for small craft advisory winds with
areas of gusts up to 30 kt. Rough seas up to 12 ft. Rain
likely.

Saturday: moderate risk for small craft advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft. Slight chance of
rain.

Tides coastal flooding
South to southeast winds Friday will come as astronomical tides
are trending higher. The winds will build seas offshore to 12-14
feet. Forecast guidance also shows a zone of 15-second wave
periods extending from the gulf of maine into massachusetts bay.

All of this shows a potential for building seas along the south
coast Friday, where the flow is onshore, and into parts of the
mass east coast.

This is still a ways in the future, but it will bear watching
for potential coastal splashover or minor flooding Friday.

Box watches warnings advisories
Ct... None.

Ma... None.

Ri... None.

Marine... Gale warning until 10 pm est this evening for anz232>235-237-
255-256.

Gale warning until 9 pm est this evening for anz230.

Gale warning until 11 pm est this evening for anz231.

Gale warning until 1 pm est this afternoon for anz236.

Gale warning until midnight est tonight for anz250-251-254.

Synopsis... Wtb belk
near term... Wtb bw
short term... Belk
long term... Wtb
aviation... Wtb bw
marine... Wtb belk
tides coastal flooding...



Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Nantucket, Nantucket Memorial Airport, MA168 mi56 minNW 20 G 2610.00 miFair and Breezy33°F12°F43%1009 hPa

Wind History from ACK (wind in knots)
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Last 24hrW11
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W13W14
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W12W14W16
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G36
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1 day agoE17
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E12
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E13NE16
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NE14
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NE16NE16
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NE14NE13NE10N10NE12N11N14N20
G25
NW17
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NW13
2 days agoNE3NE5N11NE15NE18NE18
G27
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NE13NE15NE12NE15
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NE12
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E11E13E16
G26
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G21
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G29
E17
G26
E18
G25

Tide / Current Tables for
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Weather Map and Satellite Images
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NOTE: East coast views moved to GEOS-16. They are experimental and not well supported by NOAA so they may not be correct so be warned. This change required redoing a large amount of the GOES code. If the image you are expecting is not showing, please let me know. You may need to use the EDIT function to update your location.
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Wind Forecast for Boston, MA (13,3,4,5)
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Ground Weather Radar Station Upton, NY
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Disclaimer:
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.