Marine Weather Net

Nantucket Sound Marine Forecast


5 - 10


10 - 15


15 - 20


15 - 20

The Marine Weather Forecast In Detail:
ANZ232 Forecast Issued: 325 AM EDT Thu May 24 2018

Today...E Winds 5 To 10 Kt. Seas Around 2 Ft. Areas Of Fog This Morning With Vsby 1 Nm Or Less.
Tonight...Sw Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 3 Ft.
Fri...Sw Winds 15 To 20 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft.
Fri Night...Sw Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt After Midnight. Gusts Up To 25 Kt. Seas 2 To 4 Ft.
Sat...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 4 Ft.
Sat Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt, Becoming Se 5 To 10 Kt After Midnight. Seas 2 To 3 Ft. A Chance Of Showers. Vsby 1 To 3 Nm.
Sun...E Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft. A Chance Of Showers.
Sun Night...E Winds 5 To 10 Kt. Seas 2 To 3 Ft. A Chance Of Showers.
Mon...E Winds 5 To 10 Kt. Seas 2 To 3 Ft. A Chance Of Showers.
Mon Night...Sw Winds Around 5 Kt. Seas Around 2 Ft. Patchy Fog. A Chance Of Showers. Vsby 1 To 3 Nm. 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.
SHARE THIS PAGE:           
Area Forecast Discussion
National Weather Service Boston/Norton MA
322am EDT Thu May 24 2018

Synopsis: Quiet and dry though morning, some spotty lower conditions associated with low clouds and fog where it previously rain and along the low coast. Dry, warm and humid conditions then return through Saturday. A cold front approaches from northern New England Saturday afternoon, bringing scattered showers and thunderstorms. The front stalls south of the region Sunday, with cool east winds and patchy showers lingering through the remainder of the holiday weekend. High pressure moves in with drier weather for the midweek.

Near Term - Until 6pm This Evening
130 am update... Remaining quiet. Quick glance, back door cold front slowing, stalling against W flow, convergent zone setting up over E MA. Dry air advection occurring, however over E/SE MA, higher dew- point air combined with antecedent rains, can't rule out spotty dense fog as temperatures cool beneath mostly clear conditions.

Meanwhile, several features linger offshore as discerned via GOES-16 night-time microphysics. Potential for low cloud features to expand as they progress SW, impacting Nantucket early on and potential E MA prior to sunrise. Low clouds either pushed off by mean wind or eroding into morning with daytime heating.

Today... Again, back door cold front having come ashore, stalled over E MA up against W flow. With diurnal heating, convergence zone becomes well-defined, maintained by sea-breeze influences, push back into the interior. Airmass differential, likely mixing, scattered cloud decks atop the boundary layer. Gusty E winds more likely per mesoscale isallobaric wind response, whereas gusty W winds per mix-down of faster low-level winds. In both cases, potential for gusts up around 20 mph.

Considerably drier W with 30-degree dewpoints, relative humidity down to 20 percent. Highs warming into the mid to upper 70s, whereas cooler, more moist E with onshore flow. Plenty of sunshine

Short Term - 6pm This Evening Through 6pm Friday
Tonight... Clear conditions, return light S flow, opportunity for radiational cooling with boundary layer decoupling early on before higher dewpoint air pushes N. Perhaps some low cloud and/or fog issues along the immediate S-shoreline of New England, otherwise leaning with coldest forecast guidance with lows upper 40s to low 50s.

Friday... Mild day on tap with increasing humidity. High pressure SE, W/SW flow prevails. Warm air advection within low-mid levels, ridge builds. Up against N-stream cyclonic flow / Baffin Bay low, in the confluence of which low-level SW winds increase. Daytime heating, boundary layer mixing, mix-down of drier air, faster winds. Looking at highs around the mid to upper 80s, the warm spot over the Merrimack River Valley and Boston-metro where we'll likely see some locations top out over 90. The deep mixing, can't rule out SW gusts upwards of 30 mph

Long Term - Friday Night Through Wednesday
Big Picture... Zonal flow with embedded shortwaves in place across Canada and the Northern tier of the USA. Upper flow also features closed lows over the Gulf of Mexico and the Western USA. The Western low opens and feeds into the zonal stream early next week. The Gulf low opens into the zonal flow the middle of next week. One shortwave embedded in the zonal flow will move across New England early next week.

Upper contour fields are in general agreement through Monday, while the MSLP fields show differences in details starting Sunday. Thermal fields also start showing differences starting Sunday. Overall forecast confidence is moderate-high through Sunday, moderate for Monday-Tuesday. Agreement on a building ridge Wednesday suggests higher confidence, but it is a day 7 forecast which limits such confidence.

Contour fields from Saturday onward remain above normal through the forecast period. Thermal fields are also above normal, although fall to near normal Wednesday. Low level flow turns from the east and northeast Saturday night, then remains that way for Sunday and much of Monday. This will affect the surface layer with cooler temperatures while the deeper layer remains above normal.

Concerns... Friday night and Saturday... High pressure over the West Atlantic maintains dry weather over Southern New England Friday night and Saturday morning. Low pressure passing across Northern Maine combines with the high to create a pressure gradient favoring west-southwest winds in our area. This flow brings in higher moisture air, with precipitable water values around 1.3 inches...more than 1 std dev above normal but less than 2. Dew points should climb through the 50s into the lower 60s.

Temps aloft in the mixed layer favor max surface temps in the mid to upper 80s inland and cooler along the South Coast.

As the Northern Maine low pressure moves off through the Martimes, it pushes a cold front south through our area during the late afternoon and early night. PW values continue to rise, reaching 1.5 to 1.7 inches which would be near 2 std dev. Stability parameters become more favorable for convection, with CAPE 500-1000 J/Kg and Totals around 50. Mid-level lapse rates are forecast at 6-6.5C/Km. Theta-e ridge is indicated from Southern NY through CT and Northern RI. All of this supports showers and scattered t-storms with potential for local downpours. Most favored area would be CT and Northern RI, but all areas would have a chance. Winds aloft ahead of the front are rather weak, so not favoring strong wind gusts at this time.

The cold front moves south through our area Saturday night. Increasing east winds behind the front may lead to gusty winds especially over eastern Mass.

Sunday-Wednesday... Cold front stalls south of New England, aligned with the zonal flow. Shortwave trough moves east through the upper flow, passing New England around Monday. This may generate a weak wave along the front that moves past us on Monday. Thus we expect continued unsettled conditions Sunday and Monday with a chance of showers each day.

Another cold front pushes SE out of central Canada during Tuesday. This May generate a few showers before pushing the moisture offshore.

High pressure builds over the region Wednesday, bringing dry weather.

Marine Discussion
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Short Term /through Friday/...High confidence.

Tonight and Thursday... Back door cold front sweeping across the waters as of 10p will keep flow mainly NE over the waters through late Thursday. Gusts up to 20 kts possible;.

Thursday night... High pressure moving off the coast will result in SW winds developing. Enough of a low level jet may result in marginal small craft conditions with southwest wind gusts of 20 to 25 knots and marginal 3 to 5 foot seas across the outer-waters.

Outlook /Friday Night through Monday/...Moderate confidence.
Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.
Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, slight chance of thunderstorms.
Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.
Sunday: Winds less than 25 kt. Local rough seas. Chance of rain showers, slight chance of thunderstorms.
Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

Memorial Day: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
Small Craft Advisory for winds from 11am to 6pm EDT Friday for ANZ230-231-251.
Small Craft Advisory from 2pm to 8pm EDT Friday for ANZ235- 237-250.
Small Craft Advisory from 8am to 8pm EDT Friday for ANZ254>256

markerCities        markerTides        marker This Coastal Forecast