Marine Weather Net

Nantucket Sound Marine Forecast


TODAY

E
WINDS
15 - 20
KNOTS

TONIGHT

E
WINDS
20 - 25
KNOTS

MON

NW
WINDS
5 - 10
KNOTS

MON NIGHT

N
WINDS
10 - 15
KNOTS

The Marine Weather Forecast In Detail:
ANZ232 Forecast Issued: 416 AM EDT Sun Mar 29 2020

SMALL CRAFT ADVISORY IN EFFECT THROUGH LATE TONIGHT
Today...E Winds 15 To 20 Kt, Increasing To 20 To 25 Kt This Afternoon. Gusts Up To 30 Kt. Seas 3 To 5 Ft. Rain. Vsby 1 To 3 Nm.
Tonight...E Winds 20 To 25 Kt With Gusts Up To 30 Kt, Diminishing To 10 To 15 Kt With Gusts Up To 20 Kt After Midnight. Seas 3 To 5 Ft. Showers. Vsby 1 Nm Or Less.
Mon...Nw Winds 5 To 10 Kt, Becoming N 10 To 15 Kt In The Afternoon. Seas 2 To 3 Ft. A Chance Of Showers. Vsby 1 To 3 Nm.
Mon Night...N Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft. Patchy Fog. A Chance Of Showers. Vsby 1 To 3 Nm.
Tue...N Winds 10 To 15 Kt With Gusts Up To 30 Kt. Seas 3 To 5 Ft. Patchy Fog. A Chance Of Showers. Vsby 1 To 3 Nm.
Tue Night...Ne Winds 5 To 10 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft.
Wed...Ne Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft.
Wed Night And Thu...N Winds 10 To 15 Kt With Gusts Up To 30 Kt. Seas 2 To 4 Ft. A Chance Of Showers.
Thu Night...N Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 3 To 5 Ft. A Chance Of Showers. 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
428am EDT Sunday Mar 29 2020

Synopsis
Cool wet late March day across southern New England today as a warm front remains south of the region, while a secondary low develops along the front. The low lifts to the east on tonight and on Monday, but an inverted trough extends back to the region, which will keep southern New England cool and wet. Best shot for some sunshine is across the Connecticut River Valley. Scattered rain showers may transition more towards snow showers later Monday into Tuesday morning with some coatings possible mainly in the higher terrain. Mainly dry weather prevails Tuesday afternoon into Wednesday, but it will be rather cloudy and chilly especially along the coast. An ocean storm will likely remain far enough offshore for significant impacts, but some showers will still be possible sometime Thursday and/or Friday.

Near Term - Until 6pm This Evening
Highlights... * Cool wet late March day across southern New England. Gusty winds across coastal areas.

A cutoff low and its associated trough will lift from the Upper Mississippi River Valley/Upper Midwest this morning into the central Great Lakes and southern Ontario. The primary surface low will be located over Wisconsin and will lift into the central Great Lakes. A secondary low will begin developing just south of Long Island late today along the warm front associated with the primary low.

Rain expected throughout southern New England today due to the warm front south of the region in combination with a jet streak lifting into northern New England along with Nova Scotia/New Brunswick. We have strong southerly 6 to 12 degree Celsius warm air advection at 850 hPa with southern New England being on the leading edge of this warm nose. Despite such strong warm air advection aloft expect winds at 925 hPa and the surface to be out of the east, which will keep it cool. This setup with lower clouds and easterly flow tends to keep surface temperatures much cooler as suggested by the HREF and members of the HREF guidance. Due to this nudged highs toward the 5th percentile of guidance. This yields high temperatures in the low to mid 40s.

Expect a strengthening low level jet that will slide along the south coast and gradually slide eastward to the east by Monday evening. Gusty winds are expected across the higher elevations and especially across locations immediately adjacent to the coast. Gusts of 20-35 mph are possible.

The secondary low will begin developing to the south. This combined with the strong low level jet and drier air beginning to move in across the Mid Atlantic. This may allow for some instability and potentially bring a few isolated thunderstorms with the best shot along the south coast.

Short Term - 6pm This Evening Through 6pm Monday
Highlights

* Isolated thunderstorms possible this evening mainly along the south coast with rain continuing.

* Another cool, wet late March day on tap for Monday with rain showers as an inverted trough remains in place over the region.

The cutoff low will slowly rotate from the central Great Lakes/southern Quebec tonight into the eastern Great Lakes. The primary low will follow with the cutoff, while the secondary low slides offshore tonight and is east of Cape Cod on Monday.

Tonight... Still good agreement amongst deterministic and ensemble guidance on how things evolve. Best opportunity for some thunderstorm activity is along the south coast during the evening as the dry slot moves in. There is some elevated instability per the NAM guidance with a few hundred J/kg of MUCAPE along the south coast. Expect the drier air to bring an end to precipitation south of the Mass Pike late, but this will be brief.

Winds at 850 hPa gradually shift to the west, which will advect cooler air into the region. Expect early flow at 925 hPa north of the Mass Pike, while south of the Pike winds will be northerly. Low temperatures will be in the 30s across the region.

Monday... Will see low level flow out of the north/northeast, but will be weak between the low to the west and the low to the east on Monday. The secondary low will interact with the energy associated with the cutoff on Monday. This will extend a trough from the secondary low over southern New England. This coupled with cold air advection aloft will result in rain showers. Late in the afternoon and into the evening expect enough cold air to filter in that some rain will change over to snow across the higher elevations.

Nudged down surface temperatures toward the 10th percentile of guidance across much of southern New England. This is due cool northerly flow and being socked in low level clouds. The only exception is across the CT River Valley where some sun may break out. Here temperatures were nudged toward the 50th percentile of guidance, but if there is more sunshine than currently anticipated then temperatures are too low. Highs range from the upper 30s to 40s across most areas on Monday. The CT River Valley will see readings range from the mid 40s to the low 50s.

Long Term - Monday Night Through Saturday
Highlights... * Scattered rain showers may transition to snow showers Monday night with some coatings possible mainly in the higher terrain

* Bulk of scattered rain/snow showers end Tuesday morning, but remaining rather cloudy and chilly Tuesday afternoon

* An ocean storm will likely remain far enough offshore for significant impacts, but some showers possible Thu and/or Fri

Details... Monday night... Vigorous upper level energy moving across the region combined with an offshore low pressure system will allow for an inverted trough. The result will be scattered rain showers, which may transition to snow showers in some locations with cooling temps aloft Monday night. There is the potential for some coatings of snow, mainly on grassy surfaces in the high terrain where surface temps will be a few degrees cooler. Low temps will mainly be in the 30s.

Tuesday... The bulk of the scattered rain/snow showers should come to an end Tuesday morning as shortwave energy moves east of the region. Low level NNE flow will likely keep an abundance of clouds across the region which should result in a rather chilly day. High temps will mainly be in the 40s with the coolest readings along the eastern MA coast.

Wednesday through Saturday... A classic upstream blocking pattern /-NAO/ will be in place for the second half of the week. The guidance continues to indicate the development of an ocean storm as strong northern stream upper level energy dives southeast. The 00z operational runs and most of the ensembles continues to show the brunt of the upper level energy dropping southeast as opposed to digging south. This allows the ocean storm to stay far enough offshore for significant impacts. That being said, the upper level is pattern is quite complex and we are still beyond 84 hours in the model world so a track closer to the coast can not be completely ruled out. Even with an offshore track though, guidance indicates the potential for an inverted trough to bring a period of showers sometime Thursday and/or Friday.

Temperatures during the latter half of the week will remain cool especially across eastern MA with onshore flow. Highs may reach the 50s a few times in the lower CT River Valley, but will be tough to get out of the 40s across eastern MA most if not all of the week.

Marine
Extended and expanded the Small Craft Advisory due to increasing easterly winds today. This is a result of a warm front remaining south of the region along with a secondary low developing along the front. Not out of the question that the outer waters see occasional Gale Force gusts this afternoon and into this evening as a strong low level jet slides through. Waves building to 6-10 feet with the highest waves over the outer waters. Rain expected throughout today with reduced visibilities especially in areas of heavier rain.

Could have some isolated thunderstorm activity late today and into this evening. The best shot for any thunderstorm activity is across the southern waters.

Easterly winds diminishing tonight and shifting toward the north/northeast tonight. Still expect heightened seas across the ocean through Monday with rain.

Outlook /Monday Night through Thursday/... Monday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Chance of rain showers, patchy fog. Areas of visibility 1 to 3 nm.

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Slight chance of rain showers.
Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers.
Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of rain showers.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
MARINE...
Small Craft Advisory until 2am EDT Monday for ANZ232. Small Craft Advisory until 10pm EDT this evening for ANZ233- 234. Small Craft Advisory from 11am this morning to 11pm EDT this evening for ANZ230. Small Craft Advisory from 8am this morning to 2am EDT Monday for ANZ231. Small Craft Advisory until 8pm EDT this evening for ANZ236. Small Craft Advisory until 8am EDT Monday for ANZ235-237. Small Craft Advisory from 8am this morning to 8pm EDT Monday for ANZ250-251. Small Craft Advisory until 8pm EDT Monday for ANZ254. Small Craft Advisory until 8pm EDT Monday for ANZ255-256.