Cape Cod Bay Marine Forecast
|Tonight...N Winds 10 To 15 Kt, Becoming Nw 15 To 20 Kt After Midnight. Gusts Up To 25 Kt. Seas Around 2 Ft. Patchy Fog. Showers Likely, Mainly This Evening. Vsby 1 Nm Or Less, Increasing To 1 To 3 Nm After Midnight.|
|Thu...Nw Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt In The Afternoon. Gusts Up To 25 Kt. Seas 2 To 3 Ft.|
|Thu Night...N Winds 5 To 10 Kt. Seas Around 2 Ft.|
|Fri...Ne Winds 5 To 10 Kt. Seas 1 Foot Or Less.|
|Fri Night...Ne Winds 10 To 15 Kt. Gusts Up To 20 Kt After Midnight. Seas 1 Foot Or Less.|
|Sat And Sat Night...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft. A Chance Of Showers.|
|Sun...W Winds Around 10 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft.|
|Sun Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas Around 2 Ft. A Chance Of Showers.|
|Mon...Sw Winds 5 To 10 Kt. Seas 1 Foot Or Less. Showers Likely.|
|Mon Night...W Winds 10 To 15 Kt With Gusts Up To 20 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
706pm EDT Wednesday May 5 2021
Low pressure southeast of Nantucket will move northeast tonight into Nova Scotia and the Canadian Maritimes by early Thursday. Gusty northwest winds early Thursday trend lighter by afternoon with seasonable temperatures, sunshine and dry conditions. Next chance of showers arrives Friday night into Saturday, as a coastal low pressure passes offshore, although a washout is not expected. Dry and seasonably mild weather briefly returns Sunday, before yet another coastal low and rain possibly impacts the region Sunday night into Monday.
Near Term - Until 6am Thursday Morning
Weak 1002 mb low just southeast of Nantucket per latest observations and buoys. Back edge of rain shield moving thru the Worcester Hills and RI, and traversing steadily eastward. Wind shift to the WNW already across Western CT/MA, and this drier air and subsidence will continue to overspread the region overnight from west to east. Thus, a drying trend overnight from west to east. Previous forecast captures this nicely, so no major changes with this update. Earlier discussion below.
For tonight, as surface low pulls away, ongoing rains should trend lighter and more intermittent as light northerly flow trends northwest. As rain ends by mid to late evening, should see event total rainfall from a quarter inch or less across eastern MA and much of RI, with a quarter to nearly one-half inch across interior western/central MA and across most of northern CT. NW winds will trend increasingly breezy due to strengthening isallobaric/pressure gradient and cool/dry advection helping to steepen overnight lapse rates. Gusts to 25-30 mph developing late in the overnight into the pre-dawn hrs Thurs. Skies should begin to scatter out especially second half of tonight, leading to mostly clear to partly cloudy conditions. 925 mb temps fall to around +1 to +4C. Kept lows in the 40s, low 40s in the Berkshires and mid/upper 40s elsewhere.
Short Term - 6am Thursday Morning Through Thursday Night
Thursday... A broad upper-level trough centered over the Midwest will slowly move eastward on Thursday behind low-pressure and an associated cold front moving east over the Atlantic ocean. West/northwesterly flow behind the cold-front will usher in a drier air mass over southern New England with PWAT (Precipitable Water) values below 0.40". With very little moisture in the atmosphere we will be looking at mostly clear skies on Thursday. However, some model guidance has hinted at a small amount of mid-high level moisture that may allow for a few mid-high clouds to develop in the afternoon.
A tight pressure gradient between weak high pressure building in from the west and low-pressure over the Atlantic will relax as the day progresses on Thursday. This means we'll begin the day with somewhat gusty winds that will gradually diminish by the mid to late afternoon hours. The clear skies and windy conditions should allow for fairly deep mixing early that will support high temperatures in the low-mid 60s across most of southern New England on Thursday afternoon. Despite the breezy conditions to start the day, this is shaping up to be the most pleasant day of the week as a period of unsettled weather will continue into the weekend.
Thursday Night... A quiet evening on Thursday night as weak high pressure will largely dominate southern New England. Southwesterly flow aloft will advect moisture at the mid to high levels into the region that will result in increasing cloudiness overnight. This will limit radiational cooling and should keep low-temperatures in the low-mid 40s for most of southern New England by daybreak on Friday. Areas further north and west where less cloud cover is forecast should see lows dip into the upper 30s.
Long Term - Friday Through Wednesday
Highlights... * A mix of dry and seasonably mild days but also a few rounds of rain possible
Friday... Short wave ridging holds on to provide a dry and seasonably mild day with highs 60-65. Fairly pleasant with partial sunshine and light winds. Although light onshore flow will keep the coastline in the mid to upper 50s. By Friday night, upstream northern stream energy rounds the base of the northeast trough and then enters New England. This will deepen offshore low but passing well southeast of the 40N/70W benchmark. Nonetheless, this will yield increasing clouds Fri night with a risk of scattered showers toward morning.
Saturday/Sat night... As this jet energy moves across New England, downstream the offshore low continues to deepen into a Gale Center, but the upper flow is progressive, so the offshore Gale races northeast into the maritimes. Although, an inverted trough extending back across New England from the Gale Center, may have sufficient deep layer moisture and lift to support scattered showers across MA/RI/CT Sat into Sat evening, but by no means a washout with periods of dry weather too.
Sunday... Fast/progressive upper flow continues, with short wave ridging advecting across New England, providing dry and seasonably mild weather. Expecting at least partial sunshine, a modest west wind 10- 20 mph and highs 60-65.
Next Week... Northern stream remains active and may spawn another frontal wave with its rain shield potentially impacting Southern New England Sunday night into Monday. Cool but dry weather may follow behind this departing wave for Tue/Wed.
In terms of marine headlines, have modified the start time of the existing small craft advisories on the southern offshore waters until 11pm as waves have been around 3 ft so far this afternoon. Due to strengthening NW gusts, have added a small craft advisory for all our eastern waters starting at 6am until noon Thursday.
For tonight: Rain and fog decreases, visbys improving from half-1 mile to unrestricted by mid tonight. N winds around 10 kt become NW and increase to 10-20 kt with gusts to 25-30 kt by the pre-dawn hrs, strongest on the eastern waters. Seas 2-4 ft.
For Thursday: NW winds 10-20 kt with gusts 25-30 kt thru the morning hrs, then decrease to around 10 kt with gusts around 15 kt for the afternoon. Seas 2-3 ft on the eastern waters, around 3-5 ft on the southern offshore waters.
For Thursday Night: NW winds around 10 kt trend N/NE at similar speeds, gusts 10-15 kt. Seas 2-3 ft.
Outlook /Friday 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. Areas of seas approaching 5 ft. Chance of rain showers.
Saturday Night through Sunday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.
Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory from 6am to noon EDT Thursday for ANZ230- 231-250-251. Small Craft Advisory from 11pm this evening to 8pm EDT Thursday for ANZ254>256.