Marine Weather Net

Nantucket Sound Marine Forecast


TONIGHT

NE
WINDS
10 - 15
KNOTS

MON

E
WINDS
5 - 10
KNOTS

MON NIGHT

SE
WINDS
5 KNOTS

TUE

S
WINDS
5 KNOTS

The Marine Weather Forecast In Detail:
ANZ232 Forecast Issued: 716 PM EDT Sun May 24 2020

Tonight...Ne Winds 10 To 15 Kt. Gusts Up To 20 Kt This Evening. Seas 2 To 4 Ft. Patchy Fog. Patchy Drizzle After Midnight. Vsby 1 To 3 Nm.
Mon...E Winds 5 To 10 Kt. Seas 2 To 3 Ft. Patchy Fog. Patchy Drizzle. Vsby 1 Nm Or Less.
Mon Night...Se Winds Around 5 Kt. Seas 1 Foot Or Less. Patchy Fog. Patchy Drizzle. Vsby 1 Nm Or Less.
Tue...S Winds Around 5 Kt, Increasing To 5 To 10 Kt In The Afternoon. Seas Around 2 Ft. Patchy Fog. Vsby 1 Nm Or Less.
Tue Night Through Wed Night...Sw Winds 10 To 15 Kt. Seas Around 2 Ft.
Thu...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft.
Thu Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Chance Of Showers.
Fri And Fri Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 4 Ft. Showers Likely. 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
748pm EDT Sunday May 24 2020

Synopsis
High pressure east of New England will maintain cool easterly flow near the coast into Monday. Pattern change toward warmer and more summer-like conditions for the rest of the upcoming week, with rising humidity levels especially Thursday and Friday. A cold front Friday into Friday night offers the next chance at more widespread rains. Cooler and drier conditions for the weekend.

Near Term - Until 6am Monday Morning
745pm Update:

Last few visible satellite images show shield of lower stratus just have come onshore from the North Shore southward, while also filling in across southern Bristol/Plymouth Counties and into Cape Cod/Islands. The 12z HREF low cloud cover prog handling timing of these lower clouds quite well and used it to increase sky cover a bit quicker into the coastal plain and into Rhode Island through 00z/8 PM. As low-level southeast flow continues to devleop, these clouds to eventually expanding northwestward across the remainder of Southern New England late tonight and overnight. Could see some light drizzle fall from this low cloud deck given increasing (albeit shallow) moisture. Nevertheless idea for increasing clouds is on track. No other changes needed with this update.

Previous discussion follows... Marine influence with easterly flow will continue tonight as high pressure moves east of Nova Scotia with low pressure to the south. Low level flow will veer to the SE allowing low level moisture to spread inland across SNE. This will result in low clouds across Cape/Islands and SE coastal MA expanding west across the region. Some patchy fog is expected in eastern New Eng and some drizzle is also possible with weak convergence and abundant moisture below dry layer aloft. Low temps range from mid 40s to near 50.

Short Term - 6am Monday Morning Through Monday Night
Memorial Day... Weak shortwave to the north will slide east of New Eng as mid level ridge builds across New Eng. However, SE flow will persist at the surface which will maintain lots of low level moisture across the region. Followed HREF for cloud cover which indicates low clouds and patchy drizzle in the morning will gradually way to partial sunshine in the afternoon, mainly interior. However, clouds will likely linger near the coast through much of the day. Temp forecast is tricky and will depend on how much sunshine develops in the afternoon. We have highs ranging from lower 60s in east coastal MA to mid 70s in the CT valley.

Monday night... Abundant low level moisture remains which will result in low clouds returning/expanding across the region as boundary layer cools. Low clouds and patchy fog will be most pronounced in the coastal plain as low level flow becomes southerly. Milder night with clouds cover and higher dewpoints, with lows in the 50s.

Long Term - Tuesday Through Sunday
Highlights... * Midweek warm-up towards summerlike temperatures, with humidity levels on the rise. Dry conditions despite the warming temperatures.

* Unsettled especially into Friday, and turning more humid/muggy. Cold front late in the week may bring showers and thunderstorms with downpours. Timing and location still uncertain at this range.

* Chance the front may linger into Saturday, but mainly cooler and much drier weather looking into the weekend.

Details... Tuesday through Wednesday Night:

Pattern change toward warmer, more summerlike, temperatures begins on Tuesday into a good part of the upcoming workweek.

Large mid-level ridge to build into Southern New England on Tuesday and will remain in place through Wednesday night. While temperatures will be warming into the mid/upper 80s in the interior under modest low-level SW winds, moisture and humidity levels will be slowly on the rise with mixed-dewpoints in the mid 50s to lower 60s. So still fairly comfortable but will be more noticeable as we move into midweek. This moisture through midweek is also quite shallow, and so while there should be enough convective instability for some cumulus, entrainment of drier mid-level air and large-scale subsidence under the ridge will likely yield limited to nil chances for diurnally-driven showers or storms.

Warmest day of the period looks to be on Wednesday with highs in the mid to upper 80s across a good part of interior Southern New England, with cooler low-mid 70s immediate South Coast, Cape and Islands. Lows will be in the mid 50s to low 60s Tues night and into the low-mid 60s come Wednesday night. Generally light southerly winds.

Thursday through Friday:

By Thursday, mid-level ridge is forecast to shift east and will afford SW flow for a larger depth of atmosphere across Southern New England. Both dewpoints and precipitable water levels will be on the rise (PWAT (Precipitable Water) values 1.75" to near 2") and should resemble summerlike humidity levels. This will open the door for diurnal Probability of Precipitation up showers on Thursday with CAPEs still on the lower side.

Chances for showers and thunderstorms will be on the increase Thursday night but especially so on Friday or Friday night. A slow- moving cold front will be a focal point for these shower and storm chances, and given the elevated PWAT (Precipitable Water) values and slower frontal speed, that could lead to localized downpours and heavy rain footprints at least. Forecast instability values still look fairly meager at this time range, and that may limit storm potency. Guidance seems to be locking in on a Friday into Friday night timing of the front across and through Southern New England, but this is still subject to change (GFS is slower than the international guidance). Nonetheless, will be carrying Chance to Likely Probability of Precipitation for showers, with lesser chances for thunderstorms focused more in the later Friday/Friday night period.

Highs Thursday in the low-mid 80s in the interior and in the lower 70s near the coastlines, with a mild and more humid night in the 60s Thursday night. Will be cooler Friday with more cloud cover and greater potential for showers or storms with highs in the 70s to low 80s.

The Weekend:

Some uncertainty in large-scale details especially Saturday as the GFS is slower to progress the front eastward than the ECMWF/Canadian. Behind the front we'll see cooler and much drier air filter into the area, so turning a lot less humid with highs trending cooler than average for the end of May.

Marine
Lingering 5+ ft seas over southern waters will subside overnight tonight, otherwise easterly winds below SCA (Small Craft Advisory) through Mon, becoming light and variable Monday night. Vsbys reduced at times in patchy fog.

Outlook /Tuesday through Friday/... Tuesday through Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft.
Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Thursday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.
Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.
Friday: Winds less than 25 kt. Seas up to 5 ft. Rain showers likely, slight chance of thunderstorms.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
MARINE...
Small Craft Advisory until 8am EDT Monday for ANZ254>256.