Provincetown MA to Chatham MA to Nantucket MA out 20 NM Marine Forecast
| This Afternoon...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 4 To 5 Ft. Wave Detail: Se 5 Ft At 12 Seconds And Sw 2 Ft At 4 Seconds. |
| Tonight...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt, Becoming W 5 To 10 Kt After Midnight. Seas 3 To 5 Ft. Wave Detail: Se 5 Ft At 12 Seconds And Sw 2 Ft At 4 Seconds. A Chance Of Showers. Patchy Fog After Midnight With Vsby 1 Nm Or Less. |
| Wed...N Winds 5 To 10 Kt, Becoming E In The Afternoon. Seas 3 To 5 Ft. Wave Detail: Se 5 Ft At 12 Seconds And E 2 Ft At 8 Seconds. Patchy Fog. A Chance Of Showers. Vsby 1 Nm Or Less, Increasing To 1 To 3 Nm In The Afternoon. |
| Wed Night...E Winds 5 To 10 Kt. Seas 3 To 4 Ft. Wave Detail: Se 4 Ft At 11 Seconds And E 2 Ft At 8 Seconds. A Chance Of Showers. Patchy Fog In The Evening With Vsby 1 To 3 Nm. |
| Thu...Se Winds 10 To 15 Kt. Seas 3 To 4 Ft. Wave Detail: E 3 Ft At 7 Seconds And Se 3 Ft At 10 Seconds. Showers Likely. |
| Thu Night...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 3 Ft. Wave Detail: S 3 Ft At 4 Seconds And E 3 Ft At 6 Seconds. Showers Likely. |
| Fri...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 3 To 4 Ft. Showers Likely. |
| Fri Night Through Sat Night...Sw Winds 5 To 10 Kt. Seas 2 To 3 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. |
| Area Forecast Discussion National Weather Service Boston/Norton MA 116pm EDT Tuesday September 23 2025 Synopsis Warm and humid conditions today with scattered showers and a few thunderstorms developing this afternoon into tonight as a front moves into the region. Much cooler Wednesday with risk of showers continuing, then another period of widespread showers and a few thunderstorms Thursday into Thursday night as a frontal system moves into the region. Unsettled weather pattern may linger into Friday, then gradual improvement this weekend. Above normal temperatures and increasing humidity return Thursday night into the weekend. Near Term - Through Tonight Key Messages: * Warm and humid today with scattered afternoon showers and t-storms developing in the interior * More showers and a few t-storms moving across SNE tonight Pre-frontal SW flow will bring a warm and increasingly humid airmass into SNE today. Any morning stratus or patchy fog will quickly burn off leading to partly to mostly sunny skies into early afternoon before clouds increase from the north and west. 925 mb temps 18-20C will support highs upper 70s to lower 80s away from the south coast. This coupled with dewpoints climbing into the mid 60s will make it feel like a summer day with warm and humid conditions. There is a weak cold front which drops south into SNE this afternoon which will serve as a focus for scattered showers and t-storms, mainly in the interior after 2 pm. Instability is marginal with CAPES 500-1000 J/kg and effective shear 25-30 kt across northern MA so can't rule out an isolated strong storm with gusty wind but severe probs are quite low. Locally heavy rainfall will be the primary threat as PWATs (Precipitable Waters) increase to 1.75 inches. HREF indicating up to 50 percent probs of greater than 1" Quantitative Precipitation Forecast in 3 hours in northern MA 21-00z. Threat for showers and t-storms will continue into the evening as activity moves to the coast. The cold front is expected to stall near the south coast tonight with plume of deep moisture persisting across the region. Additional showers and a few t-storms will be possible through the night as a shortwave moves into the region, with activity eventually moving offshore toward daybreak as the shortwave moves to the east with decreasing moisture. Given high PWAT (Precipitable Water) airmass, localized 1-2 inch rainfall amounts will be possible through tonight, especially northern MA where highest 1 inch probs are focused. Short Term - Wednesday Key Messages: * Much cooler Wed. Risk for showers continues with low prob for thunder across CT and SW MA Cold front will settle south of New England as high pressure builds south from the Maritimes into the Gulf of Maine. This will set up a cool and moist NE flow across SNE resulting in lots of low clouds. The risk for showers will continue as additional shortwave energy approaches from the west and there may be some drizzle also. There is some marginal elevated instability across SW portion of SNE so can't rule out a rumble of thunder from CT into SW MA. Temps will remain nearly steady in the 60s, with some lower 70s possible from Springfield to Hartford. Long Term - Wednesday Night Through Monday Key Messages: * Another round of more widespread showers and a few thunderstorms Thu into Thu night * Warm weather Fri through the weekend, but unsettled Fri and possibly Sat Robust mid level trough moves slowly east from the Gt Lakes into New Eng Thu into Fri. Ahead of the trough a modest low level jet will advect anomalous moisture northward into New England with PWATs (Precipitable Waters) increasing to near 2 inches. Increasing forcing for ascent acting on this moisture will bring potential for widespread showers and a few t-storms Thu into Thu night. The exact timing for best chance of rainfall is uncertain but it will likely be sometime Thu into Thu night assocd with low level jet Thu and approaching cold front and shortwave Thu night. Also uncertain is when the showers exit but it will likely linger into Fri as mid level trough is hanging back to the west with additional shortwave energy moving through. There is not much surface instability, but elevated instability increases with the low level jet later Thu into Thu night so a few t-storms are expected although severe threat appears low given lack of instability. NBM indicating 40-60 percent probs of rainfall greater than 1 inch Thu-Thu night and 15-30 percent probs for 2 inches. Preliminary estimate is for 0.50 to 1.50 inches of rain which would be much needed. It will become humid Thu and especially Thu night as the elevated PWAT (Precipitable Water) plume moves in. Expect dewpoints climbing well into the 60s leading to a mild night Thu night and a warm and humid day on Fri. Looking ahead to next weekend, there is still uncertainty for Sat. While deterministic guidance is dry, GEFS and EPS guidance still showing moderate probs for light showers. But it is looking like a warm day with above normal temps. Then next robust northern stream shortwave tracks to the north on Sunday bringing a cold front southward into the region. There is not much moisture so the front may come through dry with warm conditions Sunday and likely into Monday as well with high pressure in control. Marine Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Wednesday...High Confidence. SCA (Small Craft Advisory) for outer waters into Wednesday for marginal seas. Winds expected to remain below SCA. SW gusts to 20 kt today, then shifting to E-NE 10- 20 kt Wed. Outlook /Wednesday Night through Saturday/... Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely. Thursday Night through Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely, slight chance of thunderstorms. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Saturday: Winds less than 25 kt. Chance of rain showers. NOAA Boston MA Office: Watches - Warnings - Advisories CT...None. MA...None. RI...None. Marine Small Craft Advisory until 2am EDT Wednesday for ANZ235-237. Small Craft Advisory until 8pm EDT Wednesday for ANZ250. Small Craft Advisory until 2pm EDT Wednesday for ANZ254>256. |
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