Marine Weather Net

Nantucket Sound Marine Forecast


OVERNIGHT

S
WINDS
5 - 10
KNOTS

THU

SE
WINDS
10 - 15
KNOTS

THU NIGHT

E
WINDS
10 - 15
KNOTS

FRI

SW
WINDS
15-20
KNOTS

The Marine Weather Forecast In Detail:
ANZ232 Forecast Issued: 1006 PM EDT Wed Mar 20 2019

SMALL CRAFT ADVISORY IN EFFECT FROM THURSDAY EVENING THROUGH FRIDAY AFTERNOON
Overnight...S Winds 5 To 10 Kt. Seas Around 2 Ft.
Thu...Se Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Afternoon. Seas Around 2 Ft.
Thu Night...E Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 3 To 4 Ft. Patchy Fog. Rain. Vsby 1 To 3 Nm, Decreasing To 1 Nm Or Less After Midnight.
Fri...S Winds 10 To 15 Kt With Gusts Up To 20 Kt, Becoming Sw 15 To 20 Kt With Gusts Up To 30 Kt In The Afternoon. Seas 4 To 5 Ft. Rain In The Morning, Then A Chance Of Showers In The Afternoon. Patchy Fog In The Morning With Vsby 1 Nm Or Less.
Fri Night...W Winds 15 To 20 Kt, Increasing To 20 To 25 Kt After Midnight. Gusts Up To 35 Kt. Seas Around 5 Ft. A Chance Of Showers In The Evening.
Sat...W Winds 20 To 25 Kt With Gusts Up To 40 Kt. Seas 5 To 6 Ft.
Sat Night...Nw Winds 15 To 20 Kt With Gusts Up To 30 Kt. Seas Around 4 Ft.
Sun...W Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas Around 3 Ft.
Sun Night...W Winds 10 To 15 Kt. Gusts Up To 20 Kt In The Evening. Seas 2 To 3 Ft.
Mon...W Winds 5 To 10 Kt. Seas Around 2 Ft.
Mon Night...W Winds 5 To 10 Kt, Becoming N 10 To 15 Kt After Midnight. Gusts Up To 25 Kt. Seas 3 To 4 Ft. A Chance Of Showers In The Evening. 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.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
956pm EDT Wednesday Mar 20 2019

Synopsis: High pressure remains in control of our weather tonight. A coastal storm impacts the region late Thursday into Friday with periods of rain, heavy at times, and strong winds. Low pressure departs through the Maritimes Friday, bringing gusty winds to Southern New England. High pressure then delivers drier air in for the weekend. A cold front sweeps south from Canada Sunday night and Monday bringing showers. High pressure delivers colder air in from Canada early next week.

Near Term - Until 6am Thursday Morning
10pm update ... Southerly winds today have resulted in dew pts rising into the 20s. Thus airmass not as dry as previous nigheights and this will result in min temps overnight not as cold as last night. Nonetheless ridge axis remains over the region overnight allowing light winds and just high clouds. Thus temps will still manage to fall into the 30s with a few upper 20s possible. Previous forecast handles this well so no major changes with this update.

Short Term - 6am Thursday Morning Through Thursday Night
Dry weather to start Thursday, and most of the eastern half of southern New England may be dry through the day. There will be an increasing risk for precipitation from west to east, especially during the afternoon. Any precipitation will likely fall as rain, and will be most likely west of the CT River by late Thursday afternoon. With some sunshine to start, and a S to SE wind, should see temperatures near to slightly above normal away from the immediate coastline

Surface low pressure from the Mid Atlantic should move over the eastern half of southern New England Thursday night. Track of the closed low at both 925 mb and 850 mb suggests this will be mainly a rain event, with some wet snow possible towards the higher terrain of the Berkshires. Precipitable water remains about 1-2 standard deviations above normal. Expecting rainfall of 0.5-1.00 inches, with locally higher amounts should any convection develop. Any instability would be elevated, and should only enhance rainfall rates

Long Term - Friday Through Wednesday
Big Picture... On the longwave scale, Hudson's Bay upper low maintains cyclonic flow over the Northeast USA through the weekend. The flow then becomes more zonal next week. At shorter scales, closed upper low sweeps from Northern Ontario over New England Friday with heigheights that are 2-3 std deviations below normal. The low then moves off through the Maritimes on Saturday. Heigheights then return to near normal or a little above during the weekend.

Expect that temperatures will trend to seasonably mild levels over the weekend. Differences in timing a cold front coming south from Canada early next week, but agreement that a cold front moves through, followed by colder temperatures the first half of the week.

Confidence is moderate over the weekend and low-moderate early next week.

Concerns... Friday-Saturday... The coastal weather system moves north of our area, allowing drier air to move in. Expect any lingering rain to taper off, although scattered showers possible through the afternoon. Breaks of sun late in the day. Winds to 25 knots aloft will be available to mix to the surface in gusts.

The central pressure of the weather system will also be deepening, which should tighten the pressure gradient and lead to increasing wind. The strongest pressure rises are expected Saturday, with 1-2 mb/hour rates. Adding to that, the upper low and its cold pool(a region of relatively cold air) sweep overhead Friday night and Saturday morning. The strong vertical temperature lapse rates should mix strong northwest winds to the surface in gusts. Cross-sections show 35-40 knot winds aloft in the mixed layer Saturday. As usual, guidance underplays these values...we will nudge wind gust guidance up about 5 knots. Moisture cross sections show deep moisture the first half of Saturday, especially during the time of strong lapse rates. Expect at least partly cloudy skies Saturday with periods of mostly cloudy possible.

Sunday through Wednesday... High pressure builds for Sunday. Temps in the mixed layer suggest max temps in the 50s

Consensus on a cold frontal passage Monday. The ECMWF shows fropa early Monday morning, while the GFS shows passage Monday afternoon/evening and the GGEM aims for early Monday night. Some models keep the supporting upper jet up on the Canadian border, while others show the right entrance region of the northern jet reaching down over Southern New England. We will maintain chance probability of precipitation for showers Monday afternoon/evening.

That right entrance region may generate a wave on the front, delaying the departure of the showers Monday night. Otherwise, high pressure builds south from Canada with cooler, drier air for Tuesday and Wednesday

Marine Discussion
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Short Term /through Thursday Night/...High confidence.

Rather light winds and seas will continue through Thursday morning. An approaching low pressure Thursday afternoon will pass through our region Thursday night. Winds increase Thursday afternoon into Thursday night. Small Craft Advisories will be needed. Depending upon timing for the strengthening of this low pressure, might see some gusts to gale force. Have much greater confidence in gusts 25-30 kt at this time.

Widespread rain develops Thursday afternoon into Thursday night, resulting in poor visibility at times.

Outlook /Friday through Monday/... Friday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain showers. Local visibility 1 nm or less.

Friday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 13 ft. Chance of rain showers, chance of snow showers. Local visibility 1 to 3 nm.

Saturday: Moderate risk for gale force winds with local gusts up to 45 kt. Rough seas up to 13 ft.

Saturday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas.
Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.
Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers

Tides / Coastal Flooding
Seeing a decent signal for onshore winds overnight Thursday into Friday. Peak surge looks to occur just after the timing of low tide early Fri morning per latest ensembles. However, lingering surge or a slower timing could lead to create coastal impacts. At this time, thinking pockets of minor coastal flooding are most likely. Astronomical tides are rather high, about 11.7 ft MLLW in Boston. The Friday morning/early afternoon high tide looks to be the high tide of greatest concern along the east coast, with the Friday morning high tide the concern for the south coast



NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
MARINE...
Small Craft Advisory from 9pm Thursday to 6pm EDT Friday for ANZ232>234.
Small Craft Advisory from midnight Thursday night to 6pm EDT Friday for ANZ231-251.
Small Craft Advisory from 6pm Thursday to 6pm EDT Friday for ANZ235-237-254-255.
Small Craft Advisory from 8pm Thursday to 6pm EDT Friday for ANZ250.
Small Craft Advisory from 1pm Thursday to 6pm EDT Friday for ANZ256.

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