Boston Harbor Marine Forecast
|Overnight...E Winds 5 To 10 Kt. Waves 1 Foot Or Less.|
|Fri...Ne Winds 5 To 10 Kt. Waves 1 Foot Or Less.|
|Fri Night...Ne Winds 10 To 15 Kt. Gusts Up To 20 Kt After Midnight. Waves 1 Foot Or Less, Then 2 To 3 Ft After Midnight. A Chance Of Rain.|
|Sat...Ne Winds 10 To 15 Kt, Increasing To 15 To 20 Kt In The Afternoon. Waves 2 To 3 Ft. A Chance Of Rain.|
|Sat Night And Sun...Ne Winds 10 To 15 Kt With Gusts Up To 20 Kt. Waves 2 To 3 Ft.|
|Sun Night...N Winds 5 To 10 Kt. Waves 1 Foot Or Less.|
|Mon Through Tue Night...Sw Winds 5 To 10 Kt. 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
1027pm EDT Thu September 28 2023
Slow moving low pressure moving off the mid Atlantic coast with a boundary extending to the north will bring rain to portions of southern New England late tonight into Saturday. The rain will be focused across western CT/MA late tonight and Friday shifting to SE New England late Friday night into Saturday. Heavy rainfall is possible, especially across western CT. High pressure builds into the region Sunday into next week, providing a stretch of dry weather along with above normal temperatures.
Near Term - Until 6am Friday Morning
Only minor tweaks to the forecast this evening. Still thinking the focus for showers overnight will be mainly across portions of CT, with some showers also possible towards the south coast of RI and MA. Thought the last runs of the HRRR, RAP and NationalBlend had a good timing for that idea. Adjusted temperatures and dew points as well to reflect observed trends.
No major changes needed to the forecast. Clouds are starting to spread into western CT and MA but no rain on the KBOX radar yet and should hold off until after midnight. Given the clouds and rather dry airmass, radiation fog isn't looking likely, however some models are hinting at the possibility for fog in NE MA where clouds from the low are less likely to reach.
Previous Discussion... Upper low moves east from the Gt Lakes as low pressure emerges off the Mid Atlantic coast. An inverted trough extending north of the low will provide a focus for developing rainfall, which appears will be focused mostly to the SW of BOX CWA. This rainfall will be enhanced by a developing SE low level jet focused into the NYC area. While the heaviest rainfall is expected to set up to the SW, rain chances will increase across western CT/MA, including the Hartford- Springfield corridor which will be on eastern edge of this rain area. We increased Probability of Precipitation here but have decreasing Probability of Precipitation further E. In fact, there is considerable dry air in the 925-700 mb layer across much of northern and eastern MA tonight which should erode rainfall as it tries to move east, so mainly dry conditions east of FIT-PVD. Lows range from upper 40s northern MA to low/mid 50s south of the Pike and near the coast.
Short Term - 6am Friday Morning Through Friday Night
* Locally heavy rain Hartford-Springfield area Friday will shift to SE New England late Friday night into Sat
The hi-res and global ensemble guidance are in good agreement on focus for heaviest rainfall remaining mostly to the SW during Fri as inverted trough and low level jet do not move much, keeping a conveyor belt of moisture across this region. Western CT/MA will be on the eastern edge of the best moisture and lift with periods of heavy rain possible, especially in the Hartford- Springfield corridor. We held off on Flood watches here as consensus of the guidance keeps heaviest rainfall to the west and SW. If axis of rainfall shifts east, watches will need to be considered.
The drier air to the east will persist across much eastern and NE MA where it may remain mostly dry Friday, other than a few showers. Then Friday night, as the upper low approaches the northern Mid Atlantic coast, the surface low shifts eastward with increasing easterly low level jet moistening the column and increasing forcing for ascent. This will result in rain focus gradually shifting to SE New England including RI and SE MA later Fri night into Sat. The ECMWF (European Centre for Medium-Range Weather Forecasts) is most aggressive with Quantitative Precipitation Forecast for this round of rain in SNE as it shows coastal low further N with a stronger low level jet in New England than other global guidance. However, we leaned toward HREF which is not as aggressive through Fri night. We will have greater confidence in Sat forecast with the 00z guidance suite as we get within the HREF window.
Max rainfall in BOX CWA (County Warning Area) will be in Hartford-Springfield area where 1.5-2.5 inches of rain is possible into Sat. However, it is important to note that rainfall forecast is much higher to the SW where hi-res guidance indicating high probs of over 5 inches of rain. If there is any eastward shift in the guidance, flood watches will have to be considered. Rainfall amounts expected to drop off to the NE and east of the lower CT valley with the least amount of rainfall across NE MA where less than 0.5" is expected into Sat. But rainfall forecast in eastern MA will be dependent on how the late Fri night/Sat period evolves and there is uncertainty with this portion of the forecast.
Long Term - Saturday Through Thursday
Key Points: * Rain exits Sat - mainly affecting south coastal areas * Dry weather dominates much of next week with above normal temps
Weekend looks to start off on a wet note, especially near South Coast, Cape Cod, and Islands as offshore low and its inverted trough head farther out to sea. From there, confidence is increasing on trending toward drier and warmer weather for much of next week. Multi-model ensemble shows ridging aloft works across eastern third of country with 500 mb heigheights rising to over 582 dm. This should bring highs well into 70s, if not some lower 80s, by midweek. For now we stuck with NMB guidance but it's likely that highs will overperform a bit from what we have forecast.
Late in week, closed upper low will start to work its way east from northern Plains and could bring a return to an unsettled pattern and colder temps, but this should occur after Thu.
Forecaster Confidence Levels:
Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.
Tonight through Friday night...High confidence.
Generally easterly winds through the period. Gusts to 20 kt tonight over southern waters, with 25 kt gusts possible over the southern waters Fri and especially Fri night. SCA (Small Craft Advisory) in effect for southern/SE waters for combination of wind and seas.
Outlook /Saturday through Tuesday/... Saturday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Chance of rain showers.
Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Slight chance of rain showers.
Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.
Sunday Night through Monday: Winds less than 25 kt. Seas up to 5 ft.
Monday Night through Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory from 4pm Friday to 8pm EDT Saturday for ANZ254. Small Craft Advisory until 8pm EDT Saturday for ANZ255-256.