Vineyard Sound Marine Forecast
|This Afternoon...Se Winds Around 10 Kt. Seas Around 2 Ft. Patchy Fog. Showers Likely. Vsby 1 To 3 Nm.|
|Tonight...E Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 3 Ft. Patchy Fog. Showers With Tstms Likely. Vsby 1 To 3 Nm.|
|Thu...Se Winds 10 To 15 Kt, Becoming S 15 To 20 Kt In The Afternoon. Gusts Up To 25 Kt. Seas 3 To 5 Ft. Patchy Fog. Showers Likely With A Chance Of Tstms. Vsby 1 Nm Or Less.|
|Thu Night...Sw Winds Around 10 Kt. Seas 3 To 5 Ft. Patchy Fog. A Chance Of Showers.|
|Fri...W Winds Around 5 Kt, Becoming Sw In The Afternoon. Seas 2 To 4 Ft. Patchy Fog.|
|Fri Night...Sw Winds Around 10 Kt. Seas 2 To 4 Ft.|
|Sat Through Sun Night...S Winds 5 To 10 Kt. Seas 2 To 3 Ft. Winds And Seas Higher In And Near Tstms. 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
138pm EDT Wednesday August 4 2021
A front moves onshore late today into Thursday, bringing showers/thunderstorms with locally very heavy rainfall and possible flooding. Drying out Thu night, Friday and into Sat along with warmer weather. Not as warm Sunday as a front enters the region along with scattered showers. Summer warmth returns early next week.
Near Term - Until 6pm This Evening
Rain showers have moved up to the Cape Cod Canal at this hour and will continue their slow march northward. Forecast is favoring the NAM3K timing as it is most representative of the current radar situation. This would mean rain making it up to northeast MA by 5-6 pm.
Forecast is on track this morning with minimal changes necessary. Impressive satellite this morning featuring a nice baroclinic leaf over the Mid Atlantic along that frontal wave. As warm air advection continues clouds will continue to thicken and lower through the day ahead of the rain. Nantucket is the only location seeing rain at the moment but is will move north through the morning and early afternoon.
Previous Discussion... Lead wave of low pressure moves offshore this morning. Bulk of shower activity has remained offshore and the morning will feature dry conditions although with lots of cloud cover. Stronger low pressure lifts north from the NC coast this afternoon with deeper moisture and increasing PWATs (Precipitable Waters) moving up along the coast this afternoon. This will result in area of showers developing and moving up along the south coast and Cape/Islands through this afternoon, possibly reaching I-95 corridor toward evening. However, much of interior SNE west of I-95 should remain dry. Temps in the interior should reach mid/upper 70s with some sunshine this morning through high clouds, but cooler near the coast and SE New Eng.
Short Term - 6pm This Evening Through 6pm Thursday
Highlights... * Heavy rainfall and localized flash flooding possible across RI and eastern MA tonight into early Thu * Axis of heaviest rainfall remains uncertain and may still shift west or east
SNE will remain between western Atlantic subtropical ridge and slow moving trough across the Great Lakes tonight. Result is deep SW flow into New Eng with a tropical connection in place. During Thu as the upper trough approaches, the deeper moisture will gradually move to the east.
Anomalous PWATs (Precipitable Waters) 2"+ will lift north across eastern New Eng tonight at the nose of a 40-50 kt low level jet. Right entrance region of a robust upper jet will provide large scale forcing for ascent leading to widespread showers lifting north across SNE tonight into Monday morning. Meanwhile, surface low pressure lifts north along a frontal boundary which moves into SNE from the SE. Strong low level convergence along the boundary acting on anomalous moisture will lead to potential for very heavy rainfall, along with a few t-storms given marginal elevated instability and strong forcing. Potential for 2-4 inches of rain within the axis of heaviest rainfall, with max rainfall rates of 1-2"/hour possible. This could lead to significant urban street flooding and rapid rises on small rivers and streams.
The challenge for this forecast is where the axis of heavy rainfall will set up which will be dependent on the boundary location. Global and hi-res guidance offer differing solutions so forecast confidence is lower than what is ideal at this time range. Consensus of the guidance favors the I-95 corridor including BOS and PVD for axis of heaviest rainfall but the ECMWF (European Centre for Medium-Range Weather Forecasts) is further west into CT and central MA while HRRR (High-Resolution Rapid Refresh) and hi- res RGEM are further east and focused more across SE MA and Cape Cod. We leaned toward the HREF LPMM which targeted the I-95 corridor into eastern MA which is also closer to the low level jet and PWAT (Precipitable Water) axis so we issued a flash flood watch for RI and eastern MA where confidence is highest at this time. However, the axis of heavy rainfall may still shift to east or west given envelope of deterministic and ensemble solutions.
Rainfall rates will be diminishing Thu morning as higher PWATs shift east with rainfall focused across eastern New Eng. Some improvement is expected Thu afternoon from west to east.
Long Term - Thursday Night Through Tuesday
Highlights... * Fri-Sat: mainly dry weather with summer heat & humidity
* Sunday: Not as hot along with scattered showers
* Early Next Week
Summer heat and humidity return
Precipitation... Mid level trough exits southern New England early Fri with good column drying, as PWATs (Precipitable Waters) decrease at or below 1 inch! This will combine with short wave ridging to support dry weather Fri into Sat. Next short wave approaches from the west late Sat, thus low risk for a few showers/T-storms late in the day across western CT/MA. Otherwise dry weather prevails thru Sat. Short wave trough and attending surface boundary Sunday yields more clouds and risk of scattered showers/T- storms. Subtropical ridge then begins to surge northward, yielding rising heigheights into southern New England early next week. Although, some of the guidance suggest potential robust short wave possible impacting the region around Tue, with an increase risk for scattered showers/T-storms.
Temperatures... Ensembles show a fairly warm signal with 850 mb temps above normal much of this period. 850 mb ensemble mean temp is +14C Fri, then warming to +17C Sat ahead of approaching s/wv trough. This should support highs 80-85 Fri and 85-90 Sat. These temps combined with dew pts in the 60s will definitely provide a summer feel. Then Sunday, short wave energy, lower heights, more clouds and scattered showers will result in temps not quite as hot, with highs 80-85. Still humid with dew pts in the 60s. Then trending warmer/hot early next week as subtropical ridge builds northward. Ensemble mean 850 mb temps around +17C Monday, supporting highs well into the 80s, then with 850 mb temps warming to +19C Tue, highs in the upper 80s to lower 90s seem plausible.
Forecaster Confidence Levels.
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Moderate Confidence through Thursday.
Wind and seas remain below SCA (Small Craft Advisory) thresholds today. Approaching low level jet will bring increasing south winds with gusts to 25-30 kt later tonight into early Thu with building seas over south coastal waters. Vsbys reduced in showers and fog tonight into Thu morning. A few t-storms possible.
/Outlook /Thursday Night through Sunday/... Thursday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.
Friday through Friday Night: Winds less than 25 kt. Seas up to 5 ft.
Saturday through Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, slight chance of thunderstorms.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...Flash Flood Watch from 8pm EDT this evening through Thursday morning for MAZ005>007-013>021. RI...Flash Flood Watch from 8pm EDT this evening through Thursday morning for RIZ001>008.
Small Craft Advisory from 2am to 8pm EDT Thursday for ANZ232>234. Small Craft Advisory from 11pm this evening to 8pm EDT Thursday for ANZ235-237. Small Craft Advisory from 8pm this evening to 8pm EDT Thursday for ANZ254>256.