Nantucket Sound Marine Forecast
| Tonight...Sw Winds Around 10 Kt. Seas Around 2 Ft. Wave Detail: Sw 1 Foot At 3 Seconds And Se 1 Foot At 7 Seconds. Patchy Fog After Midnight With Vsby 1 Nm Or Less. |
| Thu...Sw Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Afternoon. Seas Around 2 Ft. Wave Detail: Sw 2 Ft At 3 Seconds And Se 1 Foot At 7 Seconds. Patchy Fog In The Morning With Vsby 1 Nm Or Less. |
| Thu Night...Sw Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Evening. Seas Around 2 Ft. Wave Detail: Sw 2 Ft At 3 Seconds And Se 2 Ft At 7 Seconds. Patchy Fog. Vsby 1 Nm Or Less, Increasing To 1 To 3 Nm After Midnight. |
| Fri...Sw Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Afternoon. Seas Around 2 Ft. Wave Detail: Sw 2 Ft At 3 Seconds And S 1 Foot At 6 Seconds. |
| Fri Night Through Sat Night...Sw Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 2 To 3 Ft. Wave Detail: Sw 3 Ft At 5 Seconds And Se 1 Foot At 9 Seconds. |
| Sun Through Mon Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. Wave Detail: Sw 3 Ft At 5 Seconds And Se 1 Foot At 9 Seconds. 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 227pm EDT Wednesday August 5 2026 .WHAT HAS CHANGED... Issued a Heat Advisory for the majority of the region except for the Cape and Islands starting Thursday morning and continuing through Friday evening. During this time, heat index values climb to 95-99 degrees in the afternoon with elevated heat and humidity lingering through the overnight. .KEY MESSAGES... - Advisory-level heat builds into the region starting tomorrow and lingering through Friday. The heat and humidity help to fuel the chance for widely scattered thunderstorms Thursday and Friday afternoons. - Midsummer warmth and humidity continue across much of southern New England through the weekend. Afternoon pop-up thunderstorms are most likely Saturday, with a lower chance on Sunday. Unsettled weather may return early next week, although confidence remains low in the exact details. KEY MESSAGE 1...Advisory-level heat builds into the region starting tomorrow and lingering through Friday. The heat and humidity help to fuel the chance for widely scattered thunderstorms Thursday and Friday afternoon. Heat and humidity ramp up Thursday as return flow around sprawling subtropical high pressure advects a warm and humid air mass into the region. By Thursday morning, the most noticeable change will be in humidity values as dew point temperatures surge into the low 70s across the area. Still seeing guidance paint a broad area of very warm 925 mb temperatures on the order of +22-26C Thursday and Friday. These very warm low level temperatures translate to highs in the upper 80s to mid 90s. Combined with near oppressive dew points of 72-76, apparent temperatures will climb to the upper 90s, possibly near 100 at times. Greatest risk of heat indicies >100 will be found in the CT and Merrimack River Valleys where localized downslope winds likely help boost temperatures. Some uncertainty as to the magnitude of heat elsewhere resulting from cloud cover from any thunderstorms that develop Thursday and Friday afternoons. Still, at a minimum heat index values will likely reach or exceed 95 for most locations both Thursday and Friday afternoons. Finally, elevated overnight temps in the low to mid 70s paired with elevated dew points keeping heat indicies near 80 overnight. The warm overnight temperatures will be dangerous for those without adequate access to cooling, especially in urban areas. Regarding the thunderstorm potential later in the week... a few weak, upper level disturbances passing through New England combining with the high heat/humidity and just enough instability will likely be enough to Probability of Precipitation a few diurnal showers/thunderstorms each day Thursday through the weekend, with greatest chances across the interior on Thursday. Any thunderstorms that do Probability of Precipitation have the potential to produce frequent lightning, gusty winds, and torrential downpours as PWATs (Precipitable Waters) will likely be around 2.0". Given the amount of rain southern New England has seen over the last week or so, any heavy downpours could lead to localized flooding. KEY MESSAGE 2...Midsummer warmth and humidity continue across much of southern New England through the weekend. Afternoon pop-up thunderstorms are most likely Saturday, with a lower chance on Sunday. Unsettled weather may return early next week, although confidence remains low in the exact details. Confidence remains high that midsummer warmth and humidity will continue through this weekend, along with daily chances for afternoon pop-up thunderstorms. Of the two weekend days, Saturday appears to have the greater probability of showers and thunderstorms. However, a widespread washout is not anticipated. Given the abundant rainfall earlier this week, any storms capable of producing heavy downpours could lead to localized instances of flash flooding. This is reflected in the WPC Marginal Risk (Level 1 of 4) for excessive rainfall across western New England on Saturday. There is little change in the synoptic pattern, with Bermuda high pressure remaining anchored over the western Atlantic. Persistent southwesterly flow will continue to advect above-normal temperatures and increasing humidity into southern New England through the weekend. While temperatures will remain above climatological normals, they are not particularly unusual for early August. High temperatures Saturday and Sunday should climb into the upper 80s to around 90 degrees, while dewpoints remain in the lower 70s. Overnight lows in the 70s will provide little relief. This combination will result in daytime heat index values of 90 to 95 degrees, which is below Heat Advisory criteria and is why the current advisory does not extend into Saturday. Another uncertainty is the degree of afternoon cloud cover and thunderstorm development, which could temper temperatures somewhat. Forecast trends will continue to be monitored to determine whether the Heat Advisory will need to be extended into Saturday. Temperatures trend somewhat lower Monday into Tuesday as cloud cover increases and the potential for more widespread shower activity develops. Regarding thunderstorm chances, the mid-level ridge offshore gradually flattens, resulting in a more zonal flow aloft. Embedded shortwave disturbances moving through the flow should provide sufficient lift to initiate scattered afternoon and evening thunderstorms on Saturday and potentially again on Sunday, although Sunday currently appears to be the drier of the two weekend days. While deep-layer shear remains weak, with 0-6 km bulk shear generally below 30 kt, instability will be plentiful, with forecast CAPE values around 1,500 J/kg. As a result, storms should remain largely pulse-type and disorganized rather than organized severe convection. BUFKIT soundings depict tall, skinny CAPE profiles, suggesting efficient warm-rain processes and the potential for locally heavy rainfall. PWAT (Precipitable Water) values between 1.7 and 2.0 inches further support the threat of torrential downpours. In addition to localized flooding, gusty winds and frequent lightning will be the primary hazards. That said, not every community will experience thunderstorms, and many locations will remain dry, so there is no reason to cancel outdoor plans at this point. The details regarding storm coverage and placement will become clearer once convection- allowing guidance comes into range over the next couple of days. Early next week, the subtropical ridge extends across the southern CONUS while nearly zonal flow persists across the northern CONUS. This pattern will allow additional shortwave disturbances to move through the flow, bringing the potential for more widespread showers and thunderstorms Monday night into Tuesday along an approaching cold front. Confidence in the exact details remains low given the forecast lead time, so forecast refinements are likely over the coming days. Marine Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Friday... High Confidence. A few periods of gusty SW winds near 20 kts are possible tonight across the northeastern waters and Thursday across the southern waters. Winds calm Friday as high pressure builds over the region. Waters and winds will be below SCA (Small Craft Advisory) for the foreseeable future. Outlook /Thursday Night through Monday/... Friday: Winds less than 25 kt. Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Monday: Winds less than 25 kt. NOAA Boston MA Office: Watches - Warnings - Advisories CT... Heat Advisory from 11am Thursday to 8pm EDT Friday for CTZ002>004. MA... Heat Advisory from 11am Thursday to 8pm EDT Friday for MAZ003>007-010>021-026. RI... Heat Advisory from 11am Thursday to 8pm EDT Friday for RIZ001>007. Marine None. |
Boston MA Radar
Northeast Radar
East Coast Satellite