Rhode Island Sound Marine Forecast
| This Afternoon...Sw Winds 10 To 15 Kt. Seas Around 2 Ft. Wave Detail: S 2 Ft At 7 Seconds And Se 1 Foot At 8 Seconds. |
| Tonight...Sw Winds 10 To 15 Kt. Gusts Up To 20 Kt After Midnight. Seas 2 To 3 Ft. Wave Detail: S 3 Ft At 7 Seconds And W 1 Foot At 3 Seconds. |
| Sun...Sw Winds 15 To 20 Kt, Increasing To 20 To 25 Kt In The Afternoon. Seas 3 To 5 Ft. Wave Detail: S 5 Ft At 7 Seconds And Se 1 Foot At 13 Seconds. A Chance Of Showers In The Morning. |
| Sun Night...W Winds 15 To 20 Kt With Gusts Up To 25 Kt, Becoming Nw 10 To 15 Kt After Midnight. Seas 3 To 5 Ft. Wave Detail: Sw 5 Ft At 6 Seconds And W 1 Foot At 3 Seconds. |
| Mon...Ne Winds 5 To 10 Kt, Becoming S In The Afternoon. Seas 2 To 3 Ft. Wave Detail: S 3 Ft At 7 Seconds And Se 1 Foot At 13 Seconds. |
| Mon Night...Sw Winds 5 To 10 Kt. Seas Around 2 Ft. Wave Detail: S 2 Ft At 7 Seconds And Se 1 Foot At 12 Seconds. |
| Tue Through Wed Night...E Winds 10 To 15 Kt. Seas Around 2 Ft. 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 136pm EDT Sat Jun 21 2025 Synopsis One final day of dry and seasonably warm temperatures for today. A round of scattered showers and thunderstorms could then develop overnight tonight into early on Sunday, which could become strong. A multi-day stretch of extreme heat and humidity then begins on Sunday and continues through at least Tuesday, with little to no opportunity for thunderstorms. The heat and humidity then ease into the latter half of the workweek, with daily chances at showers and thunderstorms returning. Near Term - Until 6pm This Evening 410am Update: Key Messages: * Dry and seasonably warm, with modest west winds. Possible coastal seabreezes. * Highs in the mid to upper 80s, with low levels of humidity. Details: High pressure with cyclonic flow aloft (a broad northwest flow) governs SNE early this morning. Heigheights slowly rise through today, which will favor seasonably warm temperatures, along with a modest rise in humidity level but should be on the tolerable side of the ledger. Will have to watch for a possible cooling seabreeze near the eastern MA coast today, but all in all, relatively benign weather is expected to kick off the weekend. However today will likely be the last relatively seasonable day in terms of temperatures and humidity levels. Highs generally in the mid 80s. Short Term - 6pm This Evening Through Sunday Night 410am Update: Key Messages: * Monitoring for possible overnight to early morning cluster of thunderstorms, which could become strong to severe. Although the chance of occurrence is increasing, location and exact timing are still highly uncertain. * First day of an extended spell of dangerous heat and humidity begins Sunday. Extreme Heat Warnings and Heat Advisories (Berkshires) issued. Highs into the 90s, with heat indices around 100-105F. * Mainly dry weather, but couldn't rule out an isolated thunderstorm, which could become strong to severe if it develops. Tonight: The main forecast issue for tonight revolves around the track of what is currently a severe mesoscale convective system (MCS) seen in early-Saturday-morning satellite imagery over NE MN. This feature and its convectively-augmented shortwave disturbance is rotating around a building heat ridge over the mid-MS Valley with a plume of mostly capped but extreme convective instability over the mid/northern MS Valley associated with the northeastward advection of an elevated mixed layer coming off the Rocky Mtns. Models over the last few days have hinted at this for the past few days, although the track of this feature is still a bit uncertain. There is a pretty apparent split in outcomes between the global models and the convective-allowing models; the global models (GFS, ECMWF, NAM- 12) all take this feature across far northern New England or adjacent Quebec late tonight with little to no impact to SNE. On the other hand, the majority of the CAMs have trended further SW, essentially backbuilding the southern end of the MCS (Mesoscale Convective System, a complex of thunderstorms which becomes organized on a scale larger than the individual thunderstorms) into the considerably more unstable air, with a potential MCS moving over parts of or all of SNE during the pre-dawn to early Sunday morning hours (approx 3 to 8 AM). Although surface based instability progs at that time of day are essentially nil, steepening lapse rates aloft support nearly 1500 J/kg of MUCAPE with increasing effective shear to around 40-45 kt, a shear/instability space which could support embedded elevated supercells above more stable surface layer. There still is quite a bit of uncertainty regarding this feature's track and how strong it may become, were it to affect our area. The outcomes here range from passing us by to the north, to an overnight to early-day MCS capable of hail, wind damage and torrential rain. I ended up following the trends in the CAMs, which increase Probability of Precipitation into the 15-25% range for the southern coast, and increasing to around 30- 50% for northern MA. After coordinating with the neighboring WFOs, also included enhanced wording for gusty winds, hail and heavy downpours. While not set in stone, there has been an uptrend in at least some overnight/early-Sunday impact from this convective complex. Stay tuned on this situation. Sunday: While not the hottest day in the stretch, Sunday nonetheless is the first day of a multi-day stretch of dangerous heat and humidity, that looks to last well into Tuesday. While there are uncertainties on some days if we'll truly meet extreme heat criterion, the cumulative effect of at least three days of dangerous heat indices with no significant relief at night could compound the potential for developing heat illnesses. Given this, and in an effort to keep the messaging simple, we opted to make the decision now to change the existing Extreme Heat Watch over to an Extreme Heat Warning starting Sunday through Tuesday, while also adding a Heat Advisory for significantly high heat indices for the Berkshires for the same timeframe. More specifically for Sunday, the main question mark on the forecast pertains to the effect cloud cover/rain from the early part of the day holds on. As 500 mb heigheights rise to anomalously high levels even for late June, it's likely any cloud cover should dissipate to full sun by mid to late morning. 850 mb temps warm significantly to around +18 to +20C. In a full-sun setting, that will push highs well into the 90s, with highs in the lower 80s for the Cape and Islands. Increasingly muggy air will lead to heat indices around 100 to 105 degrees, with a few areas possibly reaching the upper-100s. Lows Sunday night will be very warm and muggy, in the 70s, and areas in the CT Valley have the potential to stay above 80 degrees! The other potential issue for Sunday is if we can see any afternoon thunderstorms. The strong subsidence from the heat ridge and extremely warm low-level temps leading to capping should make that less likely. Some model solutions however are showing some re- development along residual boundaries/outflow from the MCS from earlier in the day; not sure how realistic that may end up being and though I think dry weather wins out, any storm that can break the cap would have an environment more typical of central Plains instability rarely seen in New England: as much as 4500 J/kg of CAPE, steep lapse rates of 8 C/km albeit with weak shear. Thus any storm could become severe quickly, and while I did leave a 15-20% slight chance mention for thunderstorms, there's probably better chances the day ends up being dry. Long Term - Monday Through Friday Key Messages: * Dangerous heat and humidity continues Monday and Tues, with daytime high temperatures approaching the low 100s away from the coast on Tuesday. Heat indices as high as 110 degrees! * Gradually cooling off Wednesday thru Fri, although shower and storm threats then return. Details: Monday and Tuesday: Dangerous heat and humidity are expected to continue for both Monday and into Tuesday. Extreme Heat Warnings (Heat Advisories for the Berkshires) will remain in effect. Potential exists for record high temperatures, possibly approaching some of the warmest temperatures ever observed in the month of June for some of our climate sites, with no relief at night. There also won't be much help from Mother Nature to cut into the heat from thunderstorms, with dry weather expected. For Monday, the question revolves around a possible seabreeze for the eastern MA coast, as a weak high pressure cell builds offshore. If that develops, it could lead to less-hot conditions for the eastern MA coast until late in the day. While areas away from the eastern coast see highs soar into the upper 90s to lower 100s, with heat indices around 105-110. The hottest day looks to be Tuesday, as 850 mb temps warm to as much as 21 to 23C. Full sun would support daytime highs temperatures well into the 90s to the lower 100s, with upper 80s for the Cape. Heat indices should reach well into the 100s to 110F. Wednesday through Friday: It looks as though the heat ridge shifts southward into the Carolinas on Wed, which would bring less-hot temperatures to SNE. We may still eke out another 90+ degree day in the CT valley, but we should otherwise see highs in the 80s. Heat indices in the 80s to lower to mid 90s. A steadier cooldown toward more seasonable conditions with an easterly wind component taking hold for late in the week. The risk will increase for daily shower and thunderstorm chances in this period, as the ridge shifts southward and allows for the more active storm track to become more aligned across the mid-Atlantic and Northeast states. More specific details are uncertain regarding this late week shower/storm threat at this time. Marine Forecaster Confidence Levels... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Through Sunday...High confidence. Anticipating mainly sub-SCA (Small Craft Advisory) conditions through Sunday with west winds today around 10-15 kt and mainly southerly on Sunday at similar speeds, though they increase to near-SCA (Small Craft Advisory) level late in the day. Main concern for mariners in this period is the potential for strong thunderstorms affecting the waters overnight tonight into early Sunday. Outlook /Monday through Wednesday/... Winds less than 25 kt. NOAA Boston MA Office: Watches - Warnings - Advisories CT...Extreme Heat Warning from 11am Sunday to 8pm EDT Tuesday for CTZ002>004. MA...Extreme Heat Warning from 11am Sunday to 8pm EDT Tuesday for MAZ003>007-010>021-026. Heat Advisory from 11am Sunday to 8pm EDT Tuesday for MAZ002- 008-009. RI...Extreme Heat Warning from 11am Sunday to 8pm EDT Tuesday for RIZ001>007. Marine None. |
Boston MA Radar
Northeast Radar
East Coast Satellite