Nantucket Sound Marine Forecast
|This Afternoon...Ne Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft.|
|Tonight...E Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. Light Rain Likely.|
|Mon...E Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. Patchy Fog. A Chance Of Light Rain And Drizzle. Vsby 1 Nm Or Less.|
|Mon Night...S Winds 5 To 10 Kt, Becoming W After Midnight. Seas 2 To 3 Ft. Patchy Fog. A Chance Of Rain Or Patchy Drizzle. Vsby 1 Nm Or Less.|
|Tue And Tue Night...N Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft. A Chance Of Showers.|
|Wed And Wed Night...E Winds 5 To 10 Kt, Becoming Sw 10 To 15 Kt. Seas Around 2 Ft. A Chance Of Showers.|
|Thu...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 4 Ft. Showers.|
|Thu Night...N Winds 15 To 20 Kt With Gusts Up To 30 Kt. Seas 3 To 5 Ft. 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.|
| Area Forecast Discussion|
National Weather Service Boston/Norton MA
203pm EDT Sunday Oct 25 2020
Cool weather for the entire week. Canadian high pressure will build southward across Southern New England today, with cooler but dry and seasonable conditions. A weak surface low passing to our southeast tonight into Monday will bring increasing clouds with light rain and a period of onshore winds. High pressure will bring dry weather Wednesday. The remnants of Zeta could bring a soaking rain Thursday and Thursday night. A system right behind that should pass to our south Friday. Strong high pressure brings sunny skies Saturday.
Near Term - Until 6pm This Evening
Low level moisture hanging tough across eastern MA and portions of RI with numerous low strato-cu. However, these lower clouds have eroded across northern MA and this low level drier air will push south through the afternoon. Expect lower clouds to gradually scatter out from N to S. Otherwise, sunshine will be filtered through high clouds.
Previous discussion... Strong high pressure over southern Quebec will bring cool and dry conditions today with N winds turning NE. Lots of high clouds are streaming across the region ahead of system over the mid Atlantic and there are also some lower clouds in eastern MA where low level moisture is enhanced. Low level dry air to the north will gradually filter southward with decreasing dewpoints so these lower clouds will erode this afternoon and push southward. Sunshine will be filtered through high clouds with cloud cover thickening through the afternoon near the south coast.
925 mb temps only 1-3C this afternoon which will translate to highs upper 40s to lower 50s. A few degrees cooler than normal, but all-in- all a nice Fall day ahead.
Short Term - 6pm This Evening Through 6pm Monday
Our weather pattern starts to change towards a more gloomier one as we move into tonight, but especially toward overnight. Easterly flow becomes enhanced as the weak mid-Atlantic surface low progresses northward. Increasing columnar moisture advances northward isentropically, falling into the in-situ surface ridge. This should at least promote increasing top-to-bottom cloudiness through midnight. While light rains should begin to develop from the south overnight into early Monday morning, it likely will be delayed until the column can saturate up. Thus have only offered slight to lower Chance Probability of Precipitation for showers until early Monday morning. The weak surface low is essentially suppressed to the south and east, so Probability of Precipitation are also a bit higher towards southeast MA, RI and the Cape/Islands with lower Probability of Precipitation across western MA and much of CT. Through tonight, Quantitative Precipitation Forecast is only a few hundredths at most and at times the precipitation character may be more of a drizzle.
Temperatures are somewhat tricky for tonight, with a brief period of cooling (perhaps through some wet-bulb cooling effects as well) through midnight. In most areas, lows in the upper 30s to low-mid 40s should occur early in the overnight. Modest warm advection on the east flow should then allow for a slow east to west increase in temperatures into the upper 30s to upper 40s-lower 50s by daybreak.
Continued rather gloomy weather conditions in store for Monday with generally overcast skies, periods of light rain or drizzle and onshore east to southeast flow. Weak surface low passes to our east by early Monday afternoon, with the most persistent light rains taking place through the morning. By afternoon, we should see more intermittent/off-and-on rain showers and/or drizzle as there still remains a fair amount of low-level RH hanging around underneath a dryslot aloft. Our 925 mb temps actually surge to about +9 to +13C, but suspect we won't be able to fully mix to that depth. Given abundant cloudiness and periods of rain/drizzle, I sided toward some of the cooler raw guidance temps which brings daytime highs in the mid 40s to near 50 in interior MA, with lower to mid 50s for most of CT, RI and inside of I-495 in MA. Mildest temperatures near the South Coast and Cape Cod in the mid/upper 50s.
Long Term - Monday Night Through Saturday
Highlights... * Cooler than normal through the week * Best chance of rain Thursday/Thursday night with Zeta remnants
Monday night...A lot of low level moisture remains, especially before midnight, so expecting a continuation of areas of drizzle, fog, and perhaps a touch of light rain, improving toward daybreak. Lows in the 40s except 50-55 Cape Cod and the islands.
Tuesday...Mainly a cloudy day. Despite dewpoints lowering into the 30s over the interior, there will still be a bunch of mid and high cloudiness within fast westerly flow aloft. Can't rule out a stray shower. Northerly winds will keep it quite fall-like, with highs only from 50-55, except upper 50s in RI and southeast MA.
Tuesday night and Wednesday...All models show some subtle, weak warm advection Tuesday night that should maintain cloudy skies and could produce a few showers, with the best chance in CT and south coastal areas. With somewhat of a high pressure area in place over the region Wednesday, we could see some brief clearing and partial sunshine. Highs still in the 50s.
Thursday and Thursday night...The remnants of Zeta will be moving rapidly east or east-northeastward from the Ohio Valley to off the DelMarVa coast. That is the consensus of models. ECMWF (European Centre for Medium-Range Weather Forecasts) has a very strong warm front situated to our south, giving us a shot at some heavy rainfall along the south coast of RI and southeastern MA. Rain is likely throughout the forecast area, but there could be a sharp cutoff of the precipitation amounts closer to the NH/VT borders. It is way too early to know how much rain will fall and where, since it is dependent on the strength and evolution of this tropical system and its subsequent interaction with a frontal boundary.
Friday... We have discounted the GFS solution for this time period. Main issue is the track of the very strong upper low ejecting out of the southwestern U.S. on the heels of the Zeta remnants. ECMWF and CMC solutions have strong high pressure over the northeast U.S. and this upper low being shunted off the mid-Atlantic coast, well to our south. This results in a chance of showers, mainly over southern sections. Much colder weather, with highs only in the 40s, except 50- 55 Cape Cod/islands. Thursday night, at the end of the storm, temperatures could be cold enough for the rain to mix with a few flakes of snow in western MA/northwest CT before daybreak. With the low passing to our south and strong high pressure building in from the St. Lawrence Valley, strong northeast winds are likely along coastal areas. The persistent northeast flow from Thursday through Friday will cause very rough seas off the MA coast.
Worthy of mention is that the GFS, and its ensembles, depicts a quite different take on the evolution of this upper low. The upper low moves to near Cleveland and a surface low develops near New York City. The result is a wintry mess for much of northern NY and New England, including southern New England. Again, this currently is being discounted, since the ECMWF and CMC are in agreement and rather consistent.
Saturday...Strong high pressure settles in over the eastern seaboard. We are forecasting sunny skies and high temperatures within a few degrees of 50.
Small craft advisories remain in effect for most of the eastern and southern waters (excluding Boston Harbor, Narragansett Bay, and most of the southern near-shore waters).
Should see decreasing northerly winds to below SCA (Small Craft Advisory) levels by mid- morning, though the outer offshore waters will still be contending with leftover long period seas between 5-8 ft decreasing to around 4-6 ft.
For tonight into Monday, a weak surface low will enhance an easterly pressure gradient across all waters but especially the southern waters. On the southern waters, this translates to a period of lower- end SCA (Small Craft Advisory) easterly gusts by tonight (around 25 kt, perhaps a few upper 20s-kt gusts) and seas building to about 5-7 ft. Winds on the eastern waters are more borderline-SCA (Small Craft Advisory) tonight with seas around 3-5 ft. Winds and seas should start to subside below SCA (Small Craft Advisory) levels for later on Monday. Periods of light rain showers tonight into early Monday afternoon, with visibilities around 3-5 miles.
Outlook /Monday Night through Thursday/... Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain, patchy drizzle, patchy fog.
Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain, slight chance of rain showers, patchy drizzle, patchy fog. Visibility 1 to 3 nm.
Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.
Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
Wednesday: Winds less than 25 kt. Slight chance of rain showers.
Wednesday Night: Winds less than 25 kt. Chance of rain showers.
Thursday: Winds less than 25 kt. Local rough seas. Rain showers likely.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory until 5pm EDT Monday for ANZ250-254>256. Small Craft Advisory until 8pm EDT this evening for ANZ251.