Marine Weather Net

Nantucket Sound Marine Forecast


TONIGHT

S
WINDS
10 - 15
KNOTS

THU

S
WINDS
25 - 30
KNOTS

THU NIGHT

W
WINDS
15 - 20
KNOTS

FRI

W
WINDS
10 - 15
KNOTS

The Marine Weather Forecast In Detail:
ANZ232 Forecast Issued: 716 PM EST Wed Jan 23 2019

GALE WARNING IN EFFECT FROM 1 AM EST THURSDAY THROUGH THURSDAY EVENING
Tonight...S Winds 10 To 15 Kt, Increasing To 15 To 20 Kt After Midnight. Gusts Up To 35 Kt. Seas 2 To 4 Ft. A Chance Of Rain After Midnight.
Thu...S Winds 25 To 30 Kt With Gusts Up To 45 Kt. Seas 4 To 6 Ft. Areas Of Fog. Rain. Vsby 1 Nm Or Less.
Thu Night...W Winds 15 To 20 Kt With Gusts Up To 35 Kt. Seas 4 To 6 Ft. Areas Of Fog. Vsby 1 Nm Or Less.
Fri...W Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 3 To 5 Ft.
Fri Night...W Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt After Midnight. Gusts Up To 30 Kt. Seas 3 To 5 Ft.
Sat...W Winds Around 10 Kt. Seas 2 To 3 Ft.
Sat Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt, Diminishing To 5 To 10 Kt After Midnight. Seas 2 To 3 Ft. A Chance Of Snow Showers.
Sun...S Winds 5 To 10 Kt. Seas 2 To 3 Ft.
Sun Night...Sw Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 3 Ft.
Mon...Nw Winds 10 To 15 Kt With Gusts Up To 25 Kt. Seas 2 To 4 Ft.
Mon Night...N Winds 5 To 10 Kt With Gusts Up To 20 Kt. Seas 2 To 3 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.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
639pm EST Wednesday Jan 23 2019

Synopsis: The threat for showers will increase from west to east tonight, particularly toward daybreak Thursday. Heavy rain on Thursday will bring the potential for some flooding, strong to damaging wind gusts, along with unseasonably mild temperatures. Late week into weekend chill with some potential light snow / snow showers in- between. Out ahead of a potent midweek storm system, onset wintry weather followed by another soaker possible. Late week could see another Arctic blast with bitterly cold wind chills.

Near Term - Until 6am Thursday Morning
630 pm update... Cold air continues to erode over N/W MA yielding the conclusion of wintry weather precip-types. Will end the winter weather head- lines at 8 pm. Any ice accretion will be no more than a glaze, but that is all it takes to result in hazardous travel.

Previous discussion... Low pressure across the eastern Great Lakes will lift northeast into Quebec tonight. The result will be a continued strengthening SW low level jet. The bulk of the forcing/deeper moisture will remain to our west this evening with some upper level ridging still in control. Nonetheless, we still expect some light rain showers at times mainly across the interior with the focus across W MA / N CT.

We should see an increase in areal coverage and intensity of the rain showers after midnight, especially across interior S New England. The increasing southwest low level jet will transport higher dewpoints northward and also allow for rising temperatures, especially along the coastal plain. In fact, temperatures may be near or even above 50 across portions of RI/SE MA by daybreak Thu. Lastly, we will have to watch for areas of fog developing overnight particularly across the interior. This the result of milder air moving over the snowpack in place.

Short Term - 6am Thursday Morning Through 6pm Thursday
*/ Highlights... - Heavy Rain and some flooding potential Thursday - Strong to damaging wind gusts across eastern New England on Thursday

*/ Discussion... Active weather on Thursday with heavy rain/flooding potential on Thursday along with the strong to damaging wind gusts. Will break more below.

1) Heavy Rain/Flood Potential Thursday

Intensifying low pressure will track just west of southern New England Thursday. This will induce a potent southerly low level jet 4-5 standard deviations above normal. Combined this with a Pwat axis 3-4 standard deviations above normal will set the stage for heavy rain. The strong forcing will result a widespread 1 to 2 inches of rain with locally higher amounts. The greatest risk for the highest amounts will be across the western slopes of the Worcester Hills, where the very strong south to southwest LLJ will result in some enhanced upslope flow. There is enough forcing and marginal elevated instability for the low risk of a t-storm or two.

In addition to the heavy rain on Thursday, snow water equivalent measurements indicate values on the order of 1 to 2 inches across the region. High temperatures should reach well into the 50s in most locales and it is not out of the question that a few locations touch 60 across RI/SE MA. This coupled with heavy rain and dewpoints in the upper 40s to middle 50s will result in a good deal of this melting. Combined all that with a frozen ground, the potential for areas of significant urban street flooding potential exists. There also will be the risk for some river/stream flooding. Therefore...a Flood Watch remains in effect for all but the outer-Islands.

2) Strong to Damaging Wind Potential:

As low pressure tracks west of southern New England, a very strong low level jet will develop late Thursday morning and afternoon. The NAM/RGEM indicate a 925 mb LLJ of 85 to 95 knots moving across the southeast new England coast, which is 4-5 standard deviations above normal. At 850 mb, the guidance indicates over 100 knots between 18z and 22 across southeast New England.

As if often the case with southerly flow, it is uncertain how much of this wind will be able to mix down given the inversion. A good rule of thumb is to take 50 percent of the 925 mb wind, but this can be stronger if we are able to get a fine line going. A lot of the mesoscale models do show this occurring, so something will have to monitor closely. Based on the data, opted to go with a High Wind Warning for southern RI and far southeast MA. We also have gone with a wind advisory for the rest of eastern MA and RI. An expansion of these headlines a bit further westward is a possibility, but will let the midshift take a look at the 00z data. The threat of these stronger winds reaching the ground will increase where high temperatures approach 60. Given the heavy rain and the magnitude of the wind, there is the risk for some downed trees and scattered power outages

Long Term - Thursday Night Through Sunday
*/ Highligheights ... - Cold, dry conditions through late week - Watching potential outcomes Sunday along an Arctic front - Another onset wintry weather, follow-up soaker Tue-Wed - Potential late week Arctic blast

*/ Overview ... To everything, turn turn turn, there is a season, turn turn turn. A pattern relatively unchanged through the following week, for now. A spinning tropospheric polar vortex across the Hudson Bay region that has been brought about by continued N Pacific poleward sub-tropical contributions yielding higher heigheights into the Arctic, downshearing N-stream energy over N America. A broad H5 trof pattern maintaining within 5-day average H5 height ensemble means through early February across Eastern N America, -H85 temperature anomalies for the central portion of N America, New England along the E-cusp, wobbling between airmasses with surface lows cascading round the TPV occluding below Hudson Bay lower heigheights with secondary low development across the northeast.

Turn turn turn, post-frontal digging Arctic air, clipper-systems in- between. With greater downshearing, equatorward potential vorticity displacements and tropospheric folds, more robust storms per cyclo- genesis. Further in time, lower confidence with outcomes, uncertain with possible N Atlantic downstream traffic, MJO contributions. May see a break mid-February with potential mild sub-tropical Pacific low-level E wind anomalies into the CONUS.

Break down details, forecast thinking in the discussion below. Low confidence forecast starting with Friday. Greater weighting towards EC / ECens.

*/ Discussion ... Late week into Saturday ... Westerly winds, cold, dry. Scattered snow shower activity possible into the Berkshires with lake fetch. More robust outcomes with some additional mid level energy / ascent swinging through Friday night along a reinforcing, Arctic cold front. But limited moisture and an increasing measure of high pressure.

Sunday into Monday ... Additional sweeping pieces of energy beneath the Hudson Bay TPV. EC keeping separate rather than phasing, could see little outcome with just a brief warm-up to at or above seasonable levels, S winds. As alluded to by the prior forecaster, have to watch for any potential development, any focused ascent.

Tuesday through Wednesday ... Another potent storm. Onset wintry weather prior to erosion per S winds. Not ruling out lead cold air drainage, however loosening with interior surface to low-level low center over the N Great Lakes if the 23.12z EC is correct. Another soaking for S New England possible with another 1-2 inches of rain, strong S winds. Perhaps a repeat of the coming storm? Wait and see. Low confidence forecast as forecast models wobble, shift, adjust.

Thursday onward ... Return Arctic air behind a deep, stacked low center over the Hudson Bay region. Could see a return of below-zero temperatures, as well as bitterly cold, potentially dangerous wind chills.

Marine Discussion
Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Short Term /through Thursday/...Moderate confidence.
Tonight... A strong SW low level jet will result in 30 to 35 knot wind gusts across the waters. The winds will tend to occur after midnight.

Thursday... Expect strong gale force wind gusts. Gale Warnings posted for all waters. We can not rule out brief storm force wind gusts, but if they occur will be short-lived and enhanced by heavier rainfall. So if needed, we would handle those stronger winds with Special Marine Warnings.

Seas will build to between 10 and 15 feet across the outer- waters. In addition, areas of fog may become locally dense as anomalously high dewpoints move over the cold ocean.

Outlook /Thursday Night through Monday/... Thursday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 15 ft. Areas fog.

Friday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft.

Friday Night: Low risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Areas of rough seas.
Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of snow showers.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, slight chance of snow showers.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers.
Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...Flash Flood Watch from 6am EST Thursday through late Thursday night for CTZ002>004. MA...High Wind Warning from 9am to 7pm EST Thursday for MAZ018>024. Flash Flood Watch from 6am EST Thursday through late Thursday night for MAZ002>022-026.
Wind Advisory from 9am to 5pm EST Thursday for MAZ005>007- 013>017. Winter Weather Advisory until 8pm EST this evening for MAZ002- 003-008-009. RI...High Wind Warning from 9am to 7pm EST Thursday for RIZ005>008. Flash Flood Watch from 6am EST Thursday through late Thursday night for RIZ001>007.
Wind Advisory from 9am to 5pm EST Thursday for RIZ001>004.
MARINE...
Gale Warning from 1am to 9pm EST Thursday for ANZ231>235-237- 251-255-256.
Gale Warning from 7am to 7pm EST Thursday for ANZ230.
Gale Warning from 7am to 5pm EST Thursday for ANZ236.
Gale Warning until 9pm EST Thursday for ANZ250-254

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