Nantucket Sound Marine Forecast
| This Afternoon...W Winds 5 To 10 Kt. Seas 2 To 3 Ft. |
| Tonight...Nw Winds Around 5 Kt, Becoming Ne With Gusts Up To 20 Kt After Midnight. Seas 2 To 3 Ft. Patchy Fog. A Chance Of Rain. Vsby 1 Nm Or Less. |
| Sun...E Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft. Patchy Fog. Rain. Vsby 1 Nm Or Less. |
| Sun Night...E Winds 10 To 15 Kt, Becoming N 5 To 10 Kt After Midnight. Gusts Up To 25 Kt. Seas 2 To 4 Ft. Patchy Fog. Rain Likely. Vsby 1 To 3 Nm. |
| Mon And Mon Night...Nw Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft. |
| Tue And Tue Night...Nw Winds 10 To 15 Kt. Gusts Up To 20 Kt. Seas Around 2 Ft, Then 1 Foot Or Less. |
| Wed...N Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas Around 2 Ft. A Chance Of Showers. |
| Wed Night...N Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 2 To 3 Ft. 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. |
| Area Forecast Discussion National Weather Service Boston/Norton MA 1246pm EST Sat Dec 2 2023 Synopsis Mainly dry weather today with mild temperatures despite a considerable amount of cloudiness. Rain redevelops overnight and gives way to a rainy, cool Sunday, as low pressure develops south of New England. Rain continues Sunday night, but drier on Monday as the system exits. Generally dry Tuesday through Thursday, but fairly cloudy with near to below normal temperatures. Next shot for more widespread precipitation after Sunday comes potentially on Friday. Near Term - Until 6pm This Evening 845 AM * Mostly cloudy today but mainly dry & mild with a few peeks of sun possible this afternoon with highs mainly in the 50s Previous forecast is on track. The shortwave that brought light rainfall to the region last evening has departed. Model cross sections indicate that low level moisture lingers...so that has kept the region cloudy but mainly dry at mid-morning. The lingering patchy fog will burn off slowly...but mainly dry weather will prevail through the afternoon. Light westerly flow might be enough for a few peeks of sunshine this afternoon despite an abundance of cloudiness. Airmass is quite mild for this time of year with 850T between +3C and +5C. So despite an abundance of clouds expect highs to top off in the 50s across most locations and a few spots may hit the upper 50s. These high temperatures are about 10 degrees above normal for this time of year. Short Term - 6pm This Evening Through 6pm Sunday 345 AM * Mainly dry Saturday evening, then rain possible late * A rainy Sunday along with cool, brisk conditions Tonight... Mainly dry weather lingers thru the evening hours. Then overnight, robust southern stream short wave enters the MS Valley. This trough induces SW flow aloft along the eastern seaboard and is accompanied by a strong, 170 kt upper level SW jet streak, with strong thermal and moisture advection into SNE. This likely results in rain approaching the region toward daybreak Sunday. Temps remain above normal, with lows overnight only in the upper 30s to lower 40s, about 10 degs warmer than normal. Light WNW winds in the evening behind the passing weak frontal boundary. Then winds become NE toward Sunday morning, as low pressure develops over the Mid Atlantic from the approaching trough, combined with high pressure over Quebec. Sunday... Southern stream short wave moves across the OH Valley and is accompanied by a strong 170 kt upper level jet streak on its southwest periphery into SNE. Beneath this upper level jet streak is a strengthening surface low approaching New England from the southwest. Atlantic and Gulf moisture will combine with strong jet dynamics and a mid level warm front to yield a widespread rain event for SNE Sunday. Despite some CAD from 1025+ mb Quebec high, marginal airmass combined with 850 mb low tracking northwest of the region, ptype will be all rain for Sunday for SNE. Looks like a fairly steady light to moderate rain Sunday with qpf ranging from 0.25 to 0.75. No flood issues but definitely a wet, dreary and raw day. Definitely not as mild as previous days, with highs more typical for early Dec, with temps in the 40s, but it will feel cooler given the brisk ENE onshore flow. Long Term - Sunday Night Through Friday 345 AM Highlights * Soggy Sunday night into early Monday with a plain rain. Breaks of sunshine late Monam through the afternoon. Near to slightly warmer than seasonable temps. * Generally dry Tuesday to Thu, but with considerable cloudiness and below normal temps. * Next shot for widespread precipitation comes late in the week as a clipper system slides in. Sunday Night through Monday... A shortwave trough lifts from the eastern Great Lakes Sunday night into northern New England by early Mon. A shortwave ridge builds in behind it for mid/late Mon, but another trough lifts into VA/NC late on Mon. Will remain under cyclonic flow through this period. A broad low lifts through southern New England Sunday night into early Mon. A weak ridge nudges in from VA/NC on Mon. Guidance in good consensus at this point with how things evolve. Only question is how strong a the secondary coastal low is. Depending on the strength there still could be a 6 hr window of moderate rainfall due. This is depicted by the latest ECMWF (European Centre for Medium-Range Weather Forecasts) with a more lift across central/northern MA with speed/directional convergence at 850 hPa. The NAM/GFS (Global Forecast System) and GEM offer differing solutions at this juncture, but all depict more uniform flow and less lift. The result is a lighter rainfall. The majority of GEFS/EPS and GEPS ensemble members lean toward the moderate rain solution, so the forecast reflects this. Expect a dry slot to punch in late on Sunday into Mon, which will bring precipitation to an end from southwest to northeast. Suspect we may be just a bit slow on this at this point in time other than along the MA/NH/VT border. After Monam should be dry for most of the region other than along the MA/NH/VT border where there could be a few spotty showers and perhaps a bit of snow mixing in across the higher terrain. Think there could be a few breaks of sunshine, but likely more clouds than sun. Highs near seasonable levels with readings in the 40s across the interior on Monday and near 50 along the south coast. Tuesday through Thursday... Cyclonic flow in place with a few waves swinging through, but mainly to our south/southwest. The only exception is on Wednesday where a shortwave digs into the eastern Great Lakes/New England later in the day. Generally dry and quiet weather as high pressure nudges in from northern Quebec. A clipper system slides mainly to our south on Wed, but could perhaps bring some spotty rain/snow showers. Have stuck with the NBM through this timeframe as its generally got the right idea. Though suspect if this shortwave slides through on Wednesday the shower activity could be a bit more widespread than am currently advertising. Would be cold enough for some snow early on Wednesday before ptype changes over to rain during the day Wed. Will have persistent NW to NNW flow, which will advect colder air into our region. The coldest air at 850 hPa will be overhead on Thu with temps of roughly -7 to -10 degrees C. Highs will generally be in the 30s Tue-Thu, but will have some low 40s across the coastal plain especially on Tue/Wed. Low temps generally in the 20s, but there will be some teens across the interior Wednesday night into Thu. Friday... A ridge builds from the Great Lakes early Fri through New England by late in the day. A shortwave quickly lifts across the Great Lakes region later on Fri and perhaps into Sat. This may swing a clipper system through our region bringing our next opportunity for more widespread precip. Still a fair amount of uncertainty with this system, especially on the intensity and exact track of the clipper system per the GEFS/GEPS/EPS guidance evident by the large spread in intensity and location of individual member lows. Give the spread stuck generally with the NBM, but did bump Probability of Precipitation up to slight chance to indicate some risk of precipitation. Should see temps starting to climb upward as flow turns southerly or westerly bringing slightly milder, but still seasonably cool air to our region. Marine Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 345 AMhigh confidence. Today...weak frontal boundary across New England combined with high pressure offshore will yield light SW winds across the MA/RI waters. Fog this morning burns off to good vsby this afternoon. Tonight...a weak and dry frontal passage briefly shifts winds into the NW this evening. Then low pressure enters the Mid Atlantic region toward morning, shifting winds to the NE over the New England waters. Rain may overspread the RI and southern MA waters toward daybreak Sunday. Sunday...intensifying low pressure approaching New England from the southwest, combined with high pressure over Quebec will result in increasing ENE winds 15-20 kt with gusts up to 25 kt. Long fetch will result in building seas. Rain will reduce vsby. Outlook /Sunday Night through Wednesday/... Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Rain likely, patchy fog. Monday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday Night: Winds less than 25 kt. Slight chance of rain showers. Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. NOAA Boston MA Office: Watches - Warnings - Advisories CT...None. MA...None. RI...None. Marine Small Craft Advisory from 3pm Sunday to 7am EST Monday for ANZ231-250-251-254. Small Craft Advisory from 9am Sunday to 7am EST Monday for ANZ232>235-237-255-256. |
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