Saturday, August19, 2017

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 5:57AMSunset 7:39PM Saturday August 19, 2017 2:45 PM EDT (18:45 UTC) Moonrise 3:26AMMoonset 6:01PM Illumination 7% Phase: Waning Crescent; Moon at 27 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 191832
area forecast discussion
national weather service taunton ma
232 pm edt Sat aug 19 2017

A cold front will slowly cross the region today, shifting
offshore by evening. High pressure brings fair seasonable
weather Monday and Tuesday. Another cold front sweeps through
new england Wednesday, followed by more dry weather Thursday and

Near term until 7 pm this evening
230 pm update...

interesting weather along the immediate eastern ma shoreline
(from CAPE ann to nantucket) with goes-16 satellite imagery,
surface observations and web cams confirming stratus and fog
rolling back onshore as seabreeze circulation increases. The fog
erodes as it moves westward and interacts with the warm land
with temps a short distance from the coastline in the upper 80s.

For example 69 at boston logan airport and 88 at norwood ma
just to the southwest.

Expecting low clouds and fog to play tag with the eastern ma
coastline for the remainder of the day and then move offshore
this evening as surface winds veer to the south and seabreeze
circulation weakens.

Otherwise a typical summer afternoon in progress with scattered diurnal
clouds and temps well into the 80s. Surface boundary is located
along and near the i95 corridor of ri and eastern ma with winds
s-se east of the boundary and providing humid conditions with
dew pts in the u60s to l70s. Meanwhile to the west of the
boundary across ri ct and western-central ma dew pts drop off in
the upper 50s to mid 60s courtesy of west winds.

Mid level dry aloft providing a cap and precluding any TCU from
developing into showers. However can t rule out an isolated
brief shower this afternoon along the boundary in eastern ma.

Short term 7 pm this evening through 6 am Sunday
Cold front continues to move offshore and wash out, but drier
air at the sfc will still lag well behind due to the inability
to mix it out during the daylight hours. Meanwhile, low pres
continues to wrap up in quebec as fairly robust upper lvl
shortwave rotates toward new england during the late evening
hours, shifting E of the area by early am sun. This is
accompanied by a secondary spike in k-indicies and pwats through
the column as it shunts the initial dry slot to the e, similar
to comma-head style wrap-around. While forcing attendant to the
wave is relatively strong, the remnant dry air should mitigate
shower development, but the risk is non-zero. Some QPF on recent
model runs, but given the initial drying, and the moisture spike
mentioned above is quite modest, will maintain a generally dry
forecast with this update and only suggest slightly more clouds
than previous forecast. Day crew can reassess if pops might be

With little change in low-lvl moisture, maintaining dwpts in the
60s, and increased cloud cover expected, overnight mins should
once again only fall into the mid 60s at the coolest spots.

Long term Sunday through Friday
Big picture...

subtropical high maintains sultry summer weather over the
southern usa. Zonal flow over the northern usa and canada early
week amplifies during the mid and late week. Contour heights
are normal to a little above normal early week, but fall below
normal by late week. This supports warm summery weather early
week, followed by cooler, drier air moving into new england late

Model upper contour fields are similar through much of next
week. Thermal fields and surface pressure fields show a similar
distribution. This maintains confidence in the forecast data
for our area.


Sunday through Tuesday...

high pressure builds over the region during this period. Upper
trough is directly overhead Sunday morning with lingering
moisture below 800 mb but dry air above. Mid level air is at
-10c or warmer, while the destabilizing part of the cold pool is
near the canadian border. Expect dry weather Sunday with some
diurnal clouds but otherwise a fine day. Temps aloft at 13-14c
should support MAX sfc temps in the low to mid 80s.

Expect dry weather Sunday night to Tuesday, although increasing
mid and high clouds during Tuesday. Light wind flow will allow
sea breezes on Monday afternoon, but gradient on Tuesday
suggests a general southwest flow.

Mixing should reach between 800 mb and 850 mb each day. Temps
of 14-16c Monday and 16-18c on Tuesday suggest MAX sfc temps in
the 80s Monday and 85-90 Tuesday... Cooler along the coast. Slow
increase in humidity with dew points in the 60s. Winds in the
mixed layer Tuesday suggest southwest gusts 15-20 knots.

Tuesday night-Wednesday...

closed low digs over quebec and the northeast usa with
shortwave driving a cold front into through new england. Expect
showers scattered tstms with the front Tuesday night Wednesday.

Cold FROPA Wednesday brings an end to the showers, but
sufficient mixing to bring northwest gusts to 20 knots behind
the cold front.


surface high pressure builds over the region while upper trough
moves overhead. Cold pool in the upper trough moves in with
500-mb temps forecast to reach -16c to -18c by Friday. Temps at
850 mb will be 8-10c. Moisture profiles show lots of dry air
during that time but with a moist layer at 850 mb. Expect dry
weather with potential for some diurnal clouds. Expect MAX temps
in the 70s, possibly near 80 in spots.

Aviation 18z Saturday through Thursday
Forecaster confidence levels...

low - less than 30 percent.

Moderate - 30 to 60 percent.

High - greater than 60 percent.

Short term through tonight ...

1830z update...

thru sunset...

vfr most locations. The exception will be along the immediate
eastern ma coastline with MVFR ifr conditions in low clouds and
fog. Isolated brief shower possible in eastern ma otherwise dry
conditions prevail.

After sunset...

onshore winds along the eastern ma coastline shift to S and then
sw which will give way to improving conditions, likelyVFR by
03z or so. OtherwiseVFR prevails with just a low risk of brief
MVFR in isolated shower overnight.

Sunday and Sunday night...

vfr, dry weather and modest west wind.

Kbos terminal... Moderate confidence.

Low clouds and fog at 18z will play tag with the airport thru
00z or so. Thereafter winds shift from east to south and will
promote improving conditions toVFR by 03z or so.

Kbdl terminal... High confidence in taf.

Outlook Monday through Wednesday ...

Monday through Tuesday... High confidence.

Vfr. Areas of ifr in early morning fog low clouds, then improving
toVFR by each mid morning and continuing the remainder of each day.

Tuesday night-Wednesday... Moderate confidence.

Vfr with areas of MVFR CIGS vsbys in showers and scattered
thunderstorms. Ifr CIGS possible in early morning fog low clouds
especially in areas that have had some rain.

Forecaster confidence levels...

low - less than 30 percent.

Moderate - 30 to 60 percent.

High - greater than 60 percent.

Short term through tonight ... Moderate confidence.

Winds and seas will diminish this morning. Timing of current
small craft advisories seems reasonable, although conditions may
drop off more quickly than current advisories suggest. After
advisories are dropped boating conditions should remain
relatively quiet into the overnight hours, with the only issue
being some localized marine fog which may restrict visibilities,
especially on the S waters.

Outlook Sunday through Wednesday ...

Sunday through Tuesday... High confidence.

High pressure builds over the waters. Winds remain 15 knots or
less, and seas 3 feet or less. Winds pick up a little on
Tuesday, but remain 20 knots or less with seas 4 feet or less.

Tuesday night-Wednesday... Moderate confidence.

A cold front approaches from the great lakes, crossing the
waters late Wednesday or Wednesday night. Southwest winds
increase with gusts 20 to 25 knots during Wednesday. Winds shift
from the northwest Wednesday night. Seas build Tuesday night
and Wednesday reaching 5 to 6 foot heights on the outer waters.

The southwest flow may also nudge those higher seas into ri
sound as well. A small craft advisory may be needed on some of
the waters during this time.

Highest recorded dew points on august 18 in any year
pvd 76 in 2002
bdl 82 in 2002
bos 77 in 1994
orh 75 in 1987
highest dew points yesterday
pvd 76 from about 1130 to midnight edt
bdl 76 from about 630 pm to midnight edt
bos 74 from about 11 pm to 1 am edt
orh 72 from about 740 pm to 1220 am edt
so the pvd value ties highest for august 18.

Highest value at pvd for august is 80.

Highest value at pvd for anytime is 81.

Box watches warnings advisories
Ct... None.

Ma... None.

Ri... None.

Marine... Small craft advisory until 5 pm edt this afternoon for anz254.

Small craft advisory until 8 pm edt this evening for anz255-

Synopsis... Wtb doody
near term... Wtb nocera doody
short term... Doody
long term... Wtb
aviation... Wtb nocera doody
marine... Wtb doody

Weather Reporting Stations
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Airport Reports
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AirportDistAgeWind ktVisibilitySky/WeatherTempDewPtHumidityPressure
Nantucket, Nantucket Memorial Airport, MA168 mi53 minWSW 111.00 miFog/Mist73°F73°F100%1009.9 hPa

Wind History from ACK (wind in knots)
Last 24hrS12S12S11S11S13S12S13S15S18
1 day agoS7S7S7S6SW5S5S6S6S6SW6S4S5S6S6S6S8S7SE8S10SE10SE13SE11S11S11
2 days agoNE13N10--NE7SW5SW7SW6SW5CalmSE3CalmN3N3N7N7N9N5NE6NE6NE6CalmSE9S7SE8

Tide / Current Tables for
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Tide / Current Tables for
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Weather Map and Satellite Images
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Weather Map
IR Satellite Image from GEOS

GOES Local Image of Northeast    EDIT

Wind Forecast for Boston, MA (14,3,4,5)
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Ground Weather Radar Station Upton, NY
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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 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 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.