Marine Weather Net

Cape Cod Bay Marine Forecast


10 - 15


10 - 15


5 - 10


5 - 10

The Marine Weather Forecast In Detail:
ANZ231 Forecast Issued: 116 AM EDT Mon Jul 23 2018

Rest Of Tonight...Se Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Slight Chance Of Showers With Isolated Tstms. Vsby 1 To 3 Nm.
Mon...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft.
Mon Night...S Winds 5 To 10 Kt. Seas Around 2 Ft. Patchy Fog.
Tue...Se Winds 5 To 10 Kt, Becoming S 10 To 15 Kt With Gusts Up To 20 Kt In The Afternoon. Seas Around 2 Ft. Patchy Fog.
Tue Night...S Winds 5 To 10 Kt. Gusts Up To 20 Kt In The Evening. Seas Around 2 Ft.
Wed...S Winds 5 To 10 Kt, Increasing To 10 To 15 Kt With Gusts Up To 20 Kt In The Afternoon. Seas 2 To 3 Ft.
Wed Night...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Chance Of Showers.
Thu...S Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft. Showers Likely With A Chance Of Tstms. Some Tstms May Produce Heavy Rainfall.
Thu Night...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Chance Of Showers.
Fri...Sw Winds 5 To 10 Kt. Seas 2 To 3 Ft.
Fri Night...Sw Winds 5 To 10 Kt. Seas 2 To 3 Ft. A Chance Of Showers. Winds And Seas Higher In And Near Tstms. Seas Are Reported As Significant Wave Height, Which Is The Average Of The Highest Third Of The Waves. Individual Wave Heights May Be More Than Twice The Significant Wave Height.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
1100pm EDT Sunday July 22 2018

Synopsis: A tropical airmass will remain entrenched across southern New England for most of the upcoming work week. Showers and a few thunderstorms are likely Monday. Tuesday and Wednesday will be mainly dry, but there is a chance of showers or thunderstorms in western sections. A cold front will be in the vicinity Wednesday night through Friday, bringing better chances of showers and storms. Slightly lower humidity possible next Saturday.

Near Term - Until 6am Monday Morning
1035pm Update... Area of showers on latest NE regional 88D radar mosaic showing most of the shower activity across SW CT into central and W Mass, moving slightly W of due N. Another band of showers developing S of New England, mainly near and S of 40N latitude, moving northward. Should see this move into S RI/SE CT by around 05Z or so. May see this area of rain, some with heavy downpours and possibly some isolated thunderstorms, move across for at least an hour or two. Something to monitor closely around daybreak in case of training of heavier showers.

Otherwise, should see the showers move into W NH/VT/upstate NY overnight. May see some more patchy showers develop with the soupy airmass across the region on the S-SE winds.

Noting some of the lower clouds breaking up from about a KHYA- KACK line eastward, which can be seen on latest GOES-East RGB Nighttime Microphysics satellite loop. Noting cooler sea surface temps with the breaking clouds from near Nantucket eastward to the southern Gulf of Maine. However, with the low T/Td spreads, should see more low clouds and patchy fog linger along the S coast, Cape Cod and the islands.

Have updated the near term forecast to bring conditions current and incorporated trends through the remainder of the overnight.

Previous Discussion... Note...have let the High Surf Advisory expire. We are no longer expecting 7 ft seas. That said, we still do expect a moderate risk for rip currents on Monday, so beachgoers should be aware of this threat!

The overall severe weather threat remains low overnight given lack of synoptic scale forcing/poor mid level lapse rates. However, when ever your dealing with a southerly 25 to 35 knot low level jet this time of year and 70+ dewpoints, the low risk for an isolated severe thunderstorm/very localized flash flood event exists. So while a low probability, something that will have to be monitored through the night.

Most locations will only see overnight low temperatures in the 70 to 75 degree range given high dewpoints in place. Enough mixing in the boundary layer should prevent widespread/dense fog...although a bit of patchy fog is certainly possible

Short Term - 6am Monday Morning Through Monday Night
Monday... A tropical environment remains in place across southern New England with the southerly LLJ/Pwats both 2+ standard deviations above normal. The models indicate a bit better instability on Monday with Capes probably near 1000 J/KG. Therefore...we expect scattered showers and embedded t-storms with locally heavy rainfall. Appears most of the activity will be near or northwest of the Boston to Providence corridor as upper level ridge over the Atlantic begins to retrograde to the west.

The overall severe weather threat will remain low on Monday given poor mid level lapse rates and lack of deep layer shear. However...given impressive low level jet and 70+ dewpoints an isolated severe thunderstorm/very localized flash flood event can not be completely ruled out. High temperatures on Monday will be well up into the 70s to the lower 80s...but it will be very humid.

Monday night... Upper level ridge over the Atlantic continues to retrograde west Monday evening. This should bring an end to any convection...except perhaps for a few left over spot showers across the interior. It will remain quite muggy though and overnight lows will likely remain above 70 in most locations

Long Term - Tuesday Through Sunday
Tuesday... Strong high pressure ridge builds westward from the western Atlantic. Deep upper trough in the Tennessee Valley will continue. The axis of rich, tropical moisture will be pushed to our west with very dry air moving in above the moist surface air. While this leads to some instability, the air should be too dry through the column to produce more than a stray shower in central and eastern sections. But a scattered thunderstorm is possible in western MA and a portion of northern CT, closest to the moist axis. Expecting morning clouds giving way to partial sunshine and highs in the mid 80s with sultry dewpoints of 72-75.

Wednesday... Not much change in the upper pattern, although the Atlantic ridge retreats slightly and the moist axis heads slightly farther east, extending into western MA and northern CT. Expecting a partly cloudy day, with increasing clouds late. Scattered showers and thunderstorm are possible, mainly in the western half of southern New England. Still warm and very humid.

Wednesday night and Thursday... The upper flow becomes more southwesterly, instead of meridional. This allows a cold front to move slowly eastward into southern New England. There is a high likelihood of showers and some thunderstorms. Have added wording of locally heavy rainfall during this time frame, since the axis of precipitable waters above 2 inches will be over us again. There is some potential for localized urban flooding, especially with any repeat storms. High temperatures on Thursday may be held to the upper 70s and lower 80s due to the cloud cover and precipitation.

Thursday night and Friday... A brief period of drying aloft moves in late Thursday night and early Friday. But, the low levels remain very moist, with dewpoints still in the lower 70s. Both the GFS and ECMWF show a second frontal boundary...the real one...approaching from the west Friday afternoon. Skies should be partly sunny, allowing temperatures to climb into the upper 80s. Both models predict the atmosphere to be very unstable, with high CAPEs and an axis of high K indices approaching from the west. GFS is 6-12 hours faster than the ECMWF. Unlike previous days, the mid-level lapse rates may be favorable for convection. If the axis approaches at the time of maximum heating Friday afternoon, scattered strong/isolated severe thunderstorms would be possible, despite relatively weak wind fields aloft.

Saturday... Possibly some lowering humidity values, especially in western sections. Otherwise, southwest flow aloft and at the surface continues. Expecting partly sunny skies a just a slight chance of a shower. Highs in the 80s.

Sunday... Some question where the cold front stalls close to or just off the S coast. May see a weak wave moving along this front, which could through a slight chance for showers mainly S of the Mass Pike. Temps may remain a bit above seasonal levels, but rather low confidence this far out.

Marine Discussion
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Short Term /through Monday Night/... Overnight through Monday night...High confidence. Persistent S-SE winds will result in gusts around or just over 20 knots at times. Seas will slowly diminish through Monday night, but remain at or above small craft thresholds for most of the outer waters. Scattered showers and patches of fog will also reduce visibility for mariners at times.

Outlook /Tuesday through Friday/... Tuesday: Winds less than 25 kt. Seas up to 5 ft.
Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.
Wednesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers, isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, slight chance of thunderstorms.
Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain showers, slight chance of thunderstorms.
Thursday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, slight chance of thunderstorms.
Friday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory until 1am EDT Tuesday for ANZ235-237-250- 254>256

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