Nantucket Sound Marine Forecast
|Tonight...Nw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. Patchy Fog. Showers With A Slight Chance Of Tstms This Evening, Then A Chance Of Showers After Midnight. Vsby 1 Nm Or Less This Evening.|
|Wed...Nw Winds 10 To 15 Kt With Gusts Up To 20 Kt, Becoming W 5 To 10 Kt In The Afternoon. Seas 2 To 3 Ft.|
|Wed Night...Sw Winds 5 To 10 Kt, Diminishing To Around 5 Kt After Midnight. Seas Around 2 Ft.|
|Thu...Se Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Thu Night And Fri...Se Winds Around 10 Kt. Seas Around 2 Ft.|
|Fri Night...S Winds Around 10 Kt. Seas Around 2 Ft.|
|Sat Through Sun Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Chance Of. 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.|
| Area Forecast Discussion|
National Weather Service Boston/Norton MA
326pm EDT Tuesday Jun 22 2021
Any showers and storms come to an end this evening and skies clear tonight. Much drier and more seasonable airmass moves in place as high pressure builds in. Dry weather with very comfortable humidity levels persist Wednesday and Thursday. Warmer and more humid conditions return Friday and into the weekend.
Near Term - Until 6am Wednesday Morning
* Showers/storms end this evening and skies clear from west to east. Much cooler compared to the past couple of nights.
Trough lifts from the central/eastern Great Lakes into northern New England by late tonight. A mid level ridge will build into the eastern Great Lakes late tonight. At the surface a cold front will move well offshore and high pressure will build in behind it.
As the cold front exits will see showers and any thunderstorms that are leftover ending from west to east. Behind the cold front high pressure builds in ushering in much cooler and drier air. Pretty good consistency amongst CAM guidance with respect to the shower/storms moving through. Leaned toward a combination of the HREF/NERFC and WPC Quantitative Precipitation Forecast for late this afternoon and into the evening. Think most areas see 0.1 to 0.5 inches of rain, but will have locally higher amounts where 1+ inches is possible where thunderstorms have moved through.
Skies clear from west to east as high pressure builds in tonight. Northwesterly flow aloft will advect in 3 to 5 degree Celsius air at 850 hPa. Not expecting winds to decouple and shift to the NW at 5-10 mph. Given the clear skies and cooler airmass moving in should see temperatures plummet. Went with the 25th percentile of guidance, which results in readings ranging from the low to mid 40s across the higher terrain and the upper 40s to mid 50s elsewhere. There will be some upper 50 to low 60 degree readings over Cape Cod and the Islands.
Short Term - 6am Wednesday Morning Through Wednesday Night
* Dry and quiet weather as high pressure builds over southern New England. Seasonable temperatures with comfortable humidity.
Mid level ridge axis builds over the region through this period. At the surface high pressure will build over southern New England on Wednesday and moves offshore Wednesday night.
Seasonable temperatures across the region and a much more comfortable airmass in place. Temperatures top out in the 70s across the region with dew points in the 40s.
Mostly clear skies and a good radiational cooling across southern New England Wednesday night. Lows range from the mid 40s to the 50s. May need to go lower in future updates as have gone with the 25th percentile of guidance at this point in time.
Long Term - Thursday Through Tuesday
Highlights... * Mild to warm afternoons and cool nigheights through Thursday. * Summer heat and humidity returns by this weekend with the chance for scattered showers and thunderstorms.
Details... Lots of moving parts for this portion of the forecast. A low pressure is expected to pass by well to our SE Wednesday night into Thursday. HIgh pressure should then be the dominant weather feature along the Eastern Seaboard late this week into early next week. The location will be important, with the core of this high pressure south of the Maritimes. This will be close enough to result in a predominantly south to southwest flow this weekend into early next week, meaning a return to increased heat and humidity for most.
Precipitation-wise, the location of this high pressure will not likely be close enough to keep us entirely dry during this time. Looking at at least a chance for mainly afternoon and evening showers and isolated thunderstorms each day Saturday through Tuesday.
Forecaster Confidence Levels.
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Tonight through Wednesday...High confidence
Showers and storms coming to an end as a cold front sweeps through. Seas remain elevated to Small Craft Advisory levels with the same timing as the previous shift had indicated into Wednesday. Seas take the longest to diminish across the eastern and southern outer waters. NW winds of 10-15 kts with gusts up to 20 kts. Winds diminish to 5-10 kts and shift to the S/SW Wednesday afternoon.
Wednesday night...High confidence.
Light southerly to southwesterly wind as high pressure builds over the waters. Waves 2-4 ft.
Outlook /Thursday through Sunday/... Thursday: Winds less than 25 kt.
Thursday Night: Winds less than 25 kt. Slight chance of rain showers.
Friday through Saturday: Winds less than 25 kt.
Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...High Rip Current Risk until 7pm EDT this evening for MAZ023- 024. RI...High Rip Current Risk until 7pm EDT this evening for RIZ008.
Small Craft Advisory until 11am EDT Wednesday for ANZ235-237. Small Craft Advisory until 2pm EDT Wednesday for ANZ254>256.