Boston Harbor Marine Forecast
| Today...W Winds 10 To 15 Kt. Gusts Up To 25 Kt This Afternoon. Waves Around 2 Ft. |
| Tonight...Nw Winds 5 To 10 Kt With Gusts Up To 20 Kt, Becoming Ne After Midnight. Waves Around 2 Ft In The Evening, Then 1 Foot Or Less. |
| Mon...E Winds 5 To 10 Kt, Increasing To 10 To 15 Kt In The Afternoon. Waves 1 Foot Or Less, Then Around 2 Ft In The Afternoon. |
| Mon Night...S Winds 10 To 15 Kt, Becoming Sw After Midnight. Waves Around 2 Ft. |
| Tue And Tue Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Waves Around 2 Ft. |
| Wed And Wed Night...Sw Winds 10 To 15 Kt, Becoming W. Gusts Up To 25 Kt. Waves Around 2 Ft. Showers Likely. |
| Thu And Thu Night...N Winds 10 To 15 Kt, Diminishing To 5 To 10 Kt. Waves Around 2 Ft, Then 1 Foot Or Less. 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 157am EDT Sunday May 17 2026 .WHAT HAS CHANGED... No significant changes. .KEY MESSAGES... - Much above normal temps today followed by a brief cooldown near the coast Monday. Then near record heat possible Tuesday and Wednesday. - Isolated strong thunderstorms are possible in the interior Tuesday afternoon, with a better chance of scattered strong to severe storms Wednesday. - Cooler, more seasonable temperatures late in the week. KEY MESSAGE 1...Much above normal temps today followed by a brief cooldown near the coast Monday. Then near record heat possible Tuesday and Wednesday. Warmup begins today as weak shortwave moves offshore this morning followed by rising heights. Warming ahead of a backdoor front to the north with 925 mb temps rising to 19-21C will support highs into the mid-upper 80s, but upper 70s along the immediate south coast and Cape Cod. The backdoor front slips south of New Eng tonight with cooler temps and light NE winds developing. However the cooler air is shallow and will mix out Monday in the CT valley where highs get back into the 80s, with mid-upper 70s elsewhere except along the immediate coast where sea-breezes may hold temps in the upper 60s to near 70. Anomalous upper ridge builds along the east coast Tuesday with height anomalies 2-3SD above normal. 850 mb temps 18-19C and 925 mb temps near 25C will support highs in the low-mid 90s away from cooling effect of SW flow near the south coast. Record highs may be broken away from the south coast. Humidity levels will be on the rise with dewpoints climbing to 60-65 but heat indices should be similar to actual air temps. The upper ridge begins to break down Wednesday as northern stream shortwave energy rides to the north suppressing the ridge to the south. However, low level temps remain rather warm through 18z suggesting another hot day, possibly a bit cooler than Tuesday due to increased cloud cover. Expect highs into lower 90s, cooler near the south coast, with similar dewpoints to Tue. Temps will likely be turning sharply cooler mid-late afternoon as cold front moves through with showers and t-storms developing. Given this is the first heat event of the season it may have a greater impact on those vulnerable to heat related illnesses than it would in the middle of the summer. It is important to stay hydrated and avoid strenuous activity in the sun. KEY MESSAGE 2...Isolated strong thunderstorms are possible Tuesday afternoon, with a better chance of scattered strong to severe storms Wednesday. The heat and increasing humidity will result in moderate instability Tuesday with CAPES 1000-2000+ J/kg. However, forcing and deep layer shear is limited under the upper ridge and best moisture will be to the north and west. So while we can't rule out a few afternoon t- storms Tuesday in the interior we think coverage will be limited. The CSU machine learning guidance does show low probs for severe Tuesday which is likely a conditional risk on t-storms developing. Strong wind would be the main threat given inverted V soundings with steep low level lapse rates. But we think the greater severe weather risk will be Wednesday as we have stronger forcing with cold front moving into the region and stronger shear. Something to monitor going forward but at the very least expect numerous showers developing Wednesday afternoon along with scattered t-storms with risk for heavy downpours as PWATs (Precipitable Waters) increase to 1.50 to 2.00 inches which is up to 2-3SD above normal. KEY MESSAGE 3...Cooler, more seasonable temperatures late week. Cold front moves offshore Wednesday night followed by cooler and drier airmass for Thu and Fri with more seasonable temps. Dry weather expected into Fri but moisture will try to return sometime Fri night into Sat with risk of showers. Marine Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. SW gusts to 25 kt will diminish by daybreak but hazardous seas around 5 ft will linger over southern waters until this afternoon so SCAs (Small Craft Advisories) were extended here into the afternoon. Otherwise, a period of marginal W-SW SCA (Small Craft Advisory) wind gusts to 20-25 kt will develop this afternoon over the nearshore waters, diminishing tonight then becoming light NE. E-SE wind 10-15 kt Mon. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. 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. Climate Record Highs for Tuesday May 19... BOS 90/1949 BDL 94/1962 PVD 91/2017 ORH 92/1962 Record Highs for Wednesday May 20... BOS 91/1996 BDL 99/1996 PVD 95/1996 ORH 91/1903 NOAA Boston MA Office: Watches - Warnings - Advisories CT...None. MA...None. RI...None. Marine Small Craft Advisory until 5am EDT early this morning for ANZ231>234-251. Small Craft Advisory until 8am EDT this morning for ANZ235- 237-250. Small Craft Advisory until 5pm EDT this afternoon for ANZ254>256. |
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