Marine Weather Net

Cape Cod Bay Marine Forecast


TODAY

SW
WINDS
10 - 15
KNOTS

TONIGHT

W
WINDS
20 - 25
KNOTS

SAT

W
WINDS
15 - 20
KNOTS

SAT NIGHT

SW
WINDS
5 - 10
KNOTS

The Marine Weather Forecast In Detail:
ANZ231 Forecast Issued: 331 AM EST Fri Nov 22 2019

GALE WARNING IN EFFECT FROM 3 PM EST THIS AFTERNOON THROUGH LATE TONIGHT
Today...Sw Winds 10 To 15 Kt, Increasing To 15 To 20 Kt This Afternoon. Gusts Up To 30 Kt. Seas 2 To 4 Ft. A Slight Chance Of Showers This Morning, Then Showers Likely This Afternoon.
Tonight...W Winds 20 To 25 Kt With Gusts Up To 40 Kt. Seas 4 To 6 Ft. A Chance Of Showers.
Sat...W Winds 15 To 20 Kt With Gusts Up To 30 Kt, Diminishing To 10 To 15 Kt With Gusts Up To 20 Kt In The Afternoon. Seas 2 To 4 Ft.
Sat Night...Sw Winds 5 To 10 Kt. Seas Around 2 Ft. Rain Likely.
Sun...E Winds 5 To 10 Kt With Gusts Up To 20 Kt, Becoming Ne 10 To 15 Kt With Gusts Up To 30 Kt In The Afternoon. Seas 2 To 4 Ft. Rain. Vsby 1 To 3 Nm.
Sun Night...Nw Winds 15 To 20 Kt With Gusts Up To 30 Kt. Seas 3 To 5 Ft. A Chance Of Showers.
Mon...W Winds 10 To 15 Kt With Gusts Up To 20 Kt. Seas 2 To 4 Ft.
Mon Night Through Tue Night...S Winds 5 To 10 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.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
627am EST Fri Nov 22 2019

Synopsis
A warm front will move across Southern New England early this morning, giving way to cloudy skies and breezy southwest winds into the early afternoon in advance of a cold front. This cold front will bring a period of light showers, along with falling temperatures and gusty northwest winds late this afternoon through tonight. Weak high pressure then settles over the area for Saturday. Low pressure will bring rain Saturday night and Sunday as it passes near Nantucket, with the possibility of light icing across the interior due to a wintry mix at the start. Dry weather follows Monday and Tuesday as high pressure builds into the region. A cold front may bring showers Wednesday followed by dry but breezy weather on Thanksgiving.

Near Term - Until 6pm This Evening
630am Update: No significant changes.

Band of light rain showers was moving offshore, which is associated with warm front crossing region. Behind it, expect increasing SW winds this morning with cloudy skies. Current timing of cold front and associated band of showers looks good based upon latest high-res guidance. Temperatures are off to a mild start, in 40s to lower 50s, which is in line with forecast highs today. Earlier discussion follows... Though 850 mb temperatures are expected to climb into the +4 to +6C range, expecting mostly overcast skies to continue even in the wake of the warm frontal passage early this morning. That really cuts into the extent to which insolational heating can boost daytime temperatures before the front gets here. Will be looking for daytime highs in the upper 40s to mid 50s, warmest towards the South Shore, Cape Cod and the Islands. Will see SW winds increase with sustained winds 10-20 mph and around 20-30 mph in gusts. Pre-frontal mixing of stronger gusts doesn't look likely given shallow mixing depth capped by an inversion.

Guidance continues to show generally good agreement on a cold frontal passage between 17-23z CWA-wide. Have again noticed an uptick in model-derived Quantitative Precipitation Forecast, especially near/south of the Mass Pike. Did opt to raise Probability of Precipitation in this window towards solid Likelys/low Categorical levels, but even with the increase in Quantitative Precipitation Forecast, most areas will only see Quantitative Precipitation Forecast amounts a few hundredths to a tenth of an inch, and the best chance of seeing rain amounts near that high is mainly SE of a BVY-ORH-HFD line.

The bigger concern is the resulting marked increase in northwesterly gusts both over the land and the waters, this roughly occurring in lockstep with quickly falling surface temperatures. Once the 850 mb front clears the forecast area, 850 mb temps crash to -5 to -8C by 00z Saturday. This contributes to very steep low-level lapse rates primed to tap into the 45-50 kt NWly low-level flow. Should see NW gusts of 30 to near 40 mph developing by late afternoon-early tonight across most of the land areas. However, wind gusts towards Cape Cod and the Islands may approach Wind Advisory levels with gusts 40-45 mph. Entertained the idea of a short- fused wind advisory for Cape Cod but thought it was somewhat marginal especially in the absence of leafed trees, and that could mitigate adverse impact. Temperatures are likely to fall back into the 30s to low 40s by early Friday evening, and with the winds we'll be looking at wind chills in the low 20s F across the Berkshires into northern Worcester County and into the hills in northern CT.

Short Term - 6pm This Evening Through 6pm Saturday
Tonight:

Surface ridge builds into Southern New England affording clearing skies and dry weather, but continued very steep low- level lapse rates even overnight will still support a continuation of gusty winds well into the nighttime hrs. When factoring in that temperatures will continue sharply falling to lows in the 20s to near freezing, hard-pressed to really call it a good night to be outdoors as wind chills in the teens to low 20s. Will continue with gusts 30 to near 40 mph away from Cape Cod/Islands (and closer to 40-42 mph for there), and while wind gusts do subside slightly after midnight, they're still 20-30 mph and in the mid-upper 30s mph towards the Cape and Islands.

Saturday:

A pretty chilly start to Saturday, but will have plenty of sun Saturday to help boost temperatures. Mid to high clouds build in late in the day from SW to NE but overall a clear to mostly sunny day with highs upper 30s to mid 40s. Will see winds/gusts continue to lighten considerably through the day and eventually become S/SW 5-10 mph late as high pressure builds off the mid- Atlantic coast.

Long Term - Saturday Night Through Thursday
Highlights... * Rain Saturday night and Sunday, starting as a wintry mix interior. * Dry and seasonable Monday and Tuesday * Milder with scattered showers Wednesday * Dry but breezy and cooler Thanksgiving Day

Active pattern continues over weekend as southern stream trough rotates through New England, as its associated surface low tracks near Sunday. Broad trough then develops across much of CONUS next week as a northern stream short wave rotates through region Wednesday.

We continue to focus on the potential hazards associated with low pressure which is forecast to pass near Nantucket Sunday:

Interior Light Icing:

Confidence is increasing for the potential of slippery travel across interior SNE Saturday night into Sunday morning due to a wintry mix.

Keep in mind there is still a good amount of spread among EC/GFS ensemble members, showing low tracks anywhere from SE New England to a little farther east of Nantucket. Despite the range in track of surface low, which is tied to it being captured by 500 mb low, overall pattern still looks on the warm side with a lack of high pressure and cold air to the north, so the potential for any significant snow or ice across the interior remains low.

Temperature profiles and ensemble probabilities suggest rain for most of SNE for this event. That said, there are hints of cold air damming across western and north central Massachusetts, and possibly into NW Hartford County, CT which is where models show possibility of light icing Saturday night into Sunday morning, before milder air eventually scours out the low level cold and causes a change to rain. Even in a "worst case" scenario, snowfall amounts would only be around an inch with around 0.10" of icing.

Minor Coastal Flooding:

Even though we are coming into a period of high astronomical tides, we are a bit less confident with the potential for coastal flooding due to uncertainty in the track of the surface low, which will determine wind direction/fetch as well as timing of the highest surge (does it coincide with high tide)?

For the Sunday morning high tide, it looks like both the east and south coasts may be impacted due to expected E/SE flow. Expecting a storm surge of 1.0 to 1.5 ft which may cause minor flooding (less than one foot inundation AGL) of vulnerable shore roads.

Times and heigheights of high tide (MLLW) Sunday morning are: * Providence: 541 AM, 5.7 ft * Boston: 845 AM, 11.2 ft * Nantucket: 946 AM, 3.9 ft

For the Sunday evening high tide, the focus will be on the eastern MA coast including Martha's Vineyard and Nantucket as winds are from the N/NE. Storm surge will be a little higher than the morning high tide, on the order of around 2.0 ft, which would bring another possible round of minor flooding (up to one foot inundation AGL) to vulnerable shore roads. Wind direction favors the coastline from Plymouth County to the Bay side of Cape Cod as well as the Islands.

Seas offshore are forecast to reach 4 to 7 feet, so beach erosion would be minimal.

Times and heigheights of high tide (MLLW) Sunday evening are: * Boston: 917 PM, 10.5 ft * Nantucket: 1024 PM, 3.2 ft

Beyond the weekend, high pressure will bring dry and seasonable weather Monday and Tuesday. An approaching cold front will bring a milder day Wednesday along with scattered showers. Behind the front, dry but breezy and cooler weather is forecast for Thanksgiving Day.

Marine
Short Term /through Saturday/...Moderate confidence.
Gale warnings remain in effect for all waters. Winds will continue to increase on all waters to SCA (Small Craft Advisory) levels through the morning, with building seas especially southern waters. Looking at gale-force W to NW winds then settling in around mid- afternoon and continuing into the overnight hours as colder air races across the waters behind a strong cold front. Subsiding trends to winds and seas into Saturday.

Today: SW winds 10-15 mph with gusts to 25 kts thru early afternoon. Wind shift to NW and increase to 15-25 kt with gusts 35-40 kt on most waters toward late afternoon into early evening, on the lower end of that range in Boston Harbor and Narragansett Bay. Seas build to 4-8 ft southern waters early, building late to 4-6 ft for eastern waters.

Tonight: NWly gale conditions on all waters tonight. General improvement trend after midnight, with winds/gusts diminishing to SCA (Small Craft Advisory) levels earliest on the bays/harbors, longer in eastern offshore waters. Seas 5-10 ft, highest southeastern waters, with lowering trend to seas nearest the coasts.

Saturday: Early-day SCA (Small Craft Advisory) winds/gusts on eastern offshore waters, diminishing to 10-15 kts with gusts to 20 kts late Saturday. Steady fall in seas to 3-5 ft.

Outlook /Saturday Night through Tuesday/... Saturday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas.

Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain.

Sunday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Rain likely.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers.
Monday: Winds less than 25 kt. Local rough seas.

Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft.
Tuesday: Winds less than 25 kt.

Equipment
KBOX WSR-88D remains out of service. A part is on order which is scheduled to arrive today, so hopefully the radar will return to service before the end of the day.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.
MARINE...
Gale Warning from 3pm this afternoon to 3am EST Saturday for ANZ231>235-237-251. Gale Warning from 3pm this afternoon to midnight EST tonight for ANZ230-236. Gale Warning from 3pm this afternoon to 6am EST Saturday for ANZ250-254. Gale Warning from 1pm this afternoon to 4am EST Saturday for ANZ255-256.