Cape Cod Bay Marine Forecast
| Tonight...S Winds 5 To 10 Kt. Seas Around 2 Ft. Patchy Fog After Midnight With Vsby 1 To 3 Nm. |
| Wed...S Winds 5 To 10 Kt. Seas 1 Foot Or Less. Hazy. |
| Wed Night...Sw Winds 5 To 10 Kt. Seas 1 Foot Or Less. Hazy. |
| Thu...Sw Winds 5 To 10 Kt. Seas 1 Foot Or Less. |
| Thu Night And Fri...S Winds 5 To 10 Kt. Seas 1 Foot Or Less. |
| Fri Night...Se Winds Around 10 Kt, Becoming Ne After Midnight. Gusts Up To 20 Kt. Seas 2 To 4 Ft. A Chance Of Showers. |
| Sat...Ne Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 3 To 5 Ft. A Chance Of Showers. |
| Sat Night And Sun...Ne Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 3 To 5 Ft. |
| Sun Night...S Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 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 759pm EDT Tuesday May 30 2023 Synopsis Overnight fog likely south of the I-90 corridor tonight. Smoke, though less concentrated than Tuesday, will haze up the skies once again Wednesday as a warming trend begins. Very warm to hot temperatures for late in the weekend with temperatures reaching into the upper 80s to lower 90s each day. While shower and storm chances are possible Friday, a better chance is expected with a cold front on Friday night into early Saturday. However rainfall is not expected to be significant. Our weather pattern then turns cooler for the weekend into early next week with no significant or widespread rains on the horizon through at least early next week. Near Term - Until 6am Wednesday Morning 730pm Update: Expect a reddish/orange sunset as fine particulates remain suspended in the air from the plume of smoke. Satellite true- color imagery also showed a narrow smoke plume into the eastern side of Martha's Vineyard from a likely wildfire on the western end of Nantucket. We've relayed Air Quality Alerts that have been issued by MA Dept of Environmental Protection (thru midnight) and RI Division of Environmental Management (thru 10 pm). High pressure ridge lying along the south coast of MA/RI will remain more or less in place, fluctuating very little in position overnight. Guidance shows potential for stratus and fog later tonight/overnight near or just south of the surface pressure ridge axis, but in light of the dry weather we've had of late and weak moisture advection, it makes for a rather low-confidence forecast regarding the risk for mist/fog or stratus. I think the chances for stratus, mist/fog north of the PVD-HFD Route 6 corridor seems too unlikely with enough south flow. Have shrunk the areal coverage to along the immediate south coast, Cape Cod and the Islands where best shot may exist. Temps should cool off rather quickly after sundown, think lows look on track for now. Previous discussion: The smoke plume that brought reduced visibilities to southeastern MA and RI for the better part of the morning and early afternoon hours will continue to drift north and west this afternoon and evening; impacting areas from Worcester north and west after about 20Z. Fortunately, the progressive nature of this band results in the worst impacts being felt in any locality for about 3-5 hours. Even in regions where the thickest smoke plume has moved northwest of, a vivid sunset is likely with smoke and haze still on the horizon. Otherwise, tranquil conditions expected this evening as high pressure settles again settles over the region. Thankfully, per HRRR/RAP guidance, the worst of the surface based smoke moves out of our region by the early overnight hours. Winds will go calm across the interior, which coupled with clear skies, yields a decent radiational cooling night north of the I-90 corridor. South of I-90, radiational cooling will be most efficient through about midnight before a deck of low stratus/fog develops along the south coast, Cape, and Islands. Guidance is varied on how far north this fog and stratus advances, but the general consensus is that it remains just south of the city of Boston. Even with fog/stratus present south of the I-90 corridor, temperatures will drop into the 40s region wide, with low 40s possible at our most efficient radiators like Taunton and Orange. Short Term - 6am Wednesday Morning Through Wednesday Night Tomorrow... Fog and stratus will burn off quickly after sunrise thanks to daytime heating mixing out the boundary layer. Should see most if not all fog dissipating by 12-13Z with the exception of Nantucket, which may hold on to lower ceilings until 15Z or so. While it will be another seasonably chilly morning, afternoon temperatures will warm well into the 80s across the interior as 925mb temps warm to between 16-20C. Temperatures along both coastlines will be impacted by the marine layer given onshore flow/sea breezing, but will likely still warm into the 70s in light of chilly SSTs. High pressure reigns over the region through Wednesday. With the high overhead, it will be difficult to define a prevailing wind direction across the entire region, though interior southern New England should experience weak south/southwest flow. Weak pressure gradient will likely lead to the development of a seabreeze along the eastern Massachusetts coastline. HRRR/RAP smoke indicates that smoke will again haze up the skies tomorrow both at the surface and aloft, though concentrations will be much less, between 12-30 um/m^3 at the surface (compared to 60-100 um/m^3 on Tuesday). Given concentrations will be significantly lower, with less of an impact on visibility and ceilings, opted to use haze in the forecast rather than smoke. Wednesday Night... Much higher dewpoints will be the determinant factor in warmer lows overnight Wednesday given persistent high pressure and calm winds. Expecting lows to tumble only into the 50s as dews range in the upper 40s to mid 50s. Again expecting decent fog coverage south of the I-90 corridor given dewpoint depressions between 0-2F. Long Term - Thursday Through Tuesday Highlights: * Very warm to hot weather with low humidity for Thurs and Fri, with a couple days of 90+ temps in the interior. Rain/thunder chances each day look limited. * Better chances for showers/thunder later Fri night into Sat, but still some uncertainty on the timing. Front to bring much cooler temperatures and onshore breezes Sat. * Other than diurnally driven isolated showers/possible thundershowers, mainly dry weather prevails with cooler than normal temps for early next week. Details: Thursday and Friday: Very warm to hot temperatures are expected for Thurs and Fri, underneath an anomalously strong mid-level ridge over the Northeast states. Abundant sun and summerlike 850 mb temps in the mid to upper teens C range will support highs upper 80s to low 90s Thurs, and into the mid 90s away from the coast. Coastal areas mainly in the 70s to low 80s. This should be a "dry heat" (e.g. without the humidity) as dewpoints are anticipated to reach only into the middle to upper 50s. Due to subsidence from the ridge aloft, convective chances look limited to nil. There may be a somewhat better chance during the day on Fri as the ridge aloft shifts westward, in response to height falls associated with troughing moving into eastern Canada and ME, but the risk ahead of the southward-moving cold front itself looks pretty limited, with sources for lift being more localized/mesoscale in the warm sector. NAM-based guidance is bullish with instability parameters, showing 100-mb mixed-layer CAPE values around 1000 J/kg owing to dewpoints in the low to mid 60s. Given the NAM's shallow PBL mixing parameterization scheme it tends to overdo instability in situations where dry air is in place, thus have sided toward the GFS (Global Forecast System) viewpoint on instability. Either way, odds for thunder look pretty limited given limited instability and lack of obvious lifting sources. Did leave a more limited Probability of Precipitation mention for pre-frontal/warm sector showers/possible thunder. If we do get any isolated storms, poor flow/shear parameters and low instability gives impression that storms would be more garden-variety vs a strong/severe storm risk. Friday Night into Saturday: Models and their ensembles continue to vary on the timing of southward-sagging cold front. NAM looks to be the fastest around Fri late afternoon to night; ECMWF (European Centre for Medium-Range Weather Forecasts) is slower and more into the daytime hrs Sat. GFS is late-overnight to early morning Sat. Trends in the guidance over the last few days model cycles is to slow the timing down with each run. Have tried to focus higher Probability of Precipitation (30-40%) for the Fri night-early Sat timeframe, but there is uncertainty on the timing and that will also affect when we see related rain showers/possible thunder. While any rain would be welcomed, the rain we do get won't be enough to put a dent in precipitation deficits. Cold front's passage as it moves southward, will be accompanied by onshore breezes with a marked increase in speeds. When that occurs is still in some question, but it appears that later Fri night into Sat is the more favored outcome as far as timing goes. The front brings a break from the spell of very warm temps, and looks a lot cooler on Saturday with the front's passage, with highs in the lower to mid 60s coastal areas to the upper 60s to mid 70s for the interior. Sunday through Early Next Week Temperatures do recover a bit from the cooler values on Sat, but overall temperatures look to trend below normal for early June as much of the Northeast states are governed by deep troughing aloft. May be diurnal chances for showers or thundershowers each day given the troughing/cooler air aloft, however dry weather should predominate for many hours but no washouts are anticipated. Marine Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 18Z Tonight into Wednesday...High confidence. Winds and seas below SCA (Small Craft Advisory) thresholds. SE winds 10-20 kt today, becoming light and variable tonight, then SE/S winds 10-15 kt Wed. Seas up to 4 ft today over outer southern waters, otherwise 2-3 ft seas into Wed. Visibility reductions to as low as 1/4mi likely tonight due to fog and stratus across the southern Waters and Cape Cod Bay. Visibility should improve after 15Z, but 1-3SM vsby possible for the better part of Wednesday morning south of the islands. Outlook /Thursday through Sunday/... Thursday through Friday: Winds less than 25 kt. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of rain showers, isolated thunderstorms. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Slight chance of rain showers. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Sunday: Winds less than 25 kt. Seas up to 5 ft. NOAA Boston MA Office: Watches - Warnings - Advisories CT...None. MA... Air Quality Alert until midnight EDT tonight for MAZ002>016- 026. RI... Air Quality Alert until 10pm EDT this evening for RIZ001>008. Marine None. |
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