Marine Weather and Tide Forecast for Yarmouth Port, MA

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
415 PM Update:

Key Messages:

* Filtered high clouds turn overcast before midnight, with some stratus along the south coast. Turning a touch humid (by late April standards).

* Rain develops just after midnight and moves east into eastern MA/RI overnight. Brief downpours possible.

* Lows in the 50s tonight, and a few western areas stay near 60.

Details:

Mostly sunny conditions (filtered thru a canopy of high clouds) has allowed for several areas to warm into the 70s with a few low 80s in the warmer CT Valley and parts of eastern MA. Although cooler temps due to increased south flow along the immediate southern coast (60s/low 70s) or eastern MA coastal seabreezes. Been one of the milder days seen to this point in 2025. However we're in a pretty changeable weather pattern with weak high pressure well to our southeast allowing a modest southerly flow to return northward, with some marine stratus east of the Delaware shore looking to fill in N/NE tonight along our southern coastline. Many areas should stay dry through at least the first half of the night, but cloud cover should stand to increase in most areas.

The bigger disturbance responsible for our weather pattern though is a low pressure area now over central MI, which will spread a warm front through Southern New England during the second half of the night. This feature will bring a pretty robust surge in moisture levels (PWATs rise to 1.3-1.5" on SWly 850 mb jet of 45-50 kt), with some very meager elevated instability as we move into the 2nd half of the night and into early Saturday morning. Expect steady light to moderate rains spreading in from the Berkshires overnight and continue into central/eastern MA and RI toward the early overnight to pre dawn hrs (~3-6 AM); there certainly could be some downpours in some of this rain activity but we expect rain to be pretty welcomed in light of recent dry weather we've had. Wouldn't rule out a rumble of thunder too but this is more the exception. Rain should be ongoing across much of Southern New England by morning.

Lows tonight should be quite mild for late-April, and it may feel more like a early summer evening with lows in the 50s, given rising dewpoints into the 50s as well and increased S winds. Some areas, especially western CT/MA, could stay above 60F.

SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/
415 PM Update:

Key Messages:

* Rain moves offshore, but eastern MA and RI may struggle to reach the lower 60s with overcast likely stubborn.

* A few t-storms possible west of Worcester Sat afternoon, and a couple could become strong if we can clear

* Stark change in air mass toward cooler and breezy conditions Saturday night.

Saturday:

Although still rather mild and a touch on the humid side, all in all Saturday is looking to generally be a washout, especially through the morning hours as steady moderate rain with some embedded downpours gradually moves offshore. Rain should be tapering off around mid-morning in western MA and most of CT, and during the late morning to early afternoon in eastern MA and RI. Will be overcast with limited warming likely for as long as rain continues.

Besides timing the rain offshore, the main forecast uncertainty revolves around the extent to which we can shake free of cloud cover even after the rain exits. This will affect not just the temperatures, but also on potential afternoon destabilization and possible afternoon thunderstorms. Am not especially optimistic on many breaks in overcast in eastern MA and RI, where conditions from a stability perspective proving to be quite stable. Temperatures here may struggle to get into the low 60s under assumption that cloud cover will temper opportunities for diurnal warming.

Latest guidance has trended more optimistically on cloud clearing across the Berkshires, CT Valley and into Tolland and western portions of Worcester Counties during the afternoon. Some heating and the higher dewpoints in the 50s could produce enough instability to pop off scattered convective showers or thunderstorms along the cold front. There is quite a bit of variability on how much instability we could see, and with lapse rates being on the lower side, the convective setting would hinge greatly on how soon we can break out into some sunshine. HRRR mean surface based CAPE shows an axis of around 500-1000 J/kg in the above-described corridor, with a maximum (worst-case/earlier-clearing outcome) around 1000-1500 J/kg.
Scattered t-storms could develop or move east from eastern NY during the midafternoon, and we could need to watch a couple stronger cells. In fact, there is some updraft helicity tracks shown in HRRR output given a favorable deep layer shear profile. But this is conditional on there being enough heating to destabilize the atmosphere - there may be little if any development at all if cloud clearing is delayed. Airmass would likely be far more stable further east one goes with little if any t-storm threat in eastern New England. We could see highs in western New England in the mid 60s to low 70s if we can scatter out of cloud cover.

Saturday Night:

Cold front then rushes offshore during the evening to overnight hours. Strong cold and dry advection will usher in a much cooler airmass to Southern New England, with increased westerly breezes and drier air/lower dewpoints. Quite a change in airmass: our 925 mb temps tumble from around +14-16C Saturday afternoon to around 0C! Strength of the upper level low and cooler air aloft suggests the evening could still be fairly cloudy in western New England.
Lows to fall into the 40s with westerly breezes around 10-15 mph.

LONG TERM /SUNDAY THROUGH FRIDAY/
Long Term

* Cool and blustery conditions on Sunday

* Warming trend Monday through Wednesday

* Closer to normal temps Thursday and Friday with unsettled weather possible Friday

Unfortunately, after a rainy Saturday, the weather on Sunday may be just as unpleasant, with cloudy, cool, and blustery conditions. With the 500mb closed trough and cold pool over the region, cyclonic vorticity and diurnal heating will likely lead to light popcorn showers, especially north of the MA Pike. High temps Sunday wont top 60, staying in the mid to upper 50s. With CAA and a tight pressure gradient, blustery north winds could make it feel like the 40s outside. The CAA and diurnal heating will promote mixing to around 850mb, where winds increase from 30mph to 60mph towards sunset. Not sure if the 60mph winds aloft will arrive in time before the sunsets and the nocturnal inversion sets in, but wind headlines may be needed for late in the day Sunday. Gusts at the surface will likely reach the 35-45mph range, with the NBM showing low to moderate probs for 45-55mph in the high terrain.

Just in time for the beginning of the work week, the nice spring/early summer weather returns with highs warming into the low 70s on Monday and mid to upper 70s on Tuesday and Wednesday. Less windy on Monday as a mid-level ridge axis passes over the region.
Ridge axis moves east of the region Tuesday and Wednesday, allowing winds to turn southwesterly and become gusty again around 20-30mph.
A cold front moves through sometime Wednesday afternoon or evening, but dry air may keep rain or thunderstorms from forming along this front. Temperatures behind the cold front for Thursday and Friday will be more seasonable in the 60s to low 70s. Unsettled weather is possible heading into Friday as guidance hints at another possible shortwave exiting the Great Lakes.

AVIATION /23Z FRIDAY THROUGH WEDNESDAY/
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

00Z TAF Update:

Tonight: Low confidence.

Guidance is not handling current conditions well as low clouds are not materializing even as warm southerly winds blow over the cold ocean waters. Hence confidence in the forecast overnight is low. Guidance has also slowed down the onset for precipitation, now reaching western MA/CT around 9-10z, and eastern MA/RI around 11-12z.

Saturday: Moderate confidence.

Widespread MVFR (with some IFR) in bands of steady moderate rain, which begins to move offshore around 18-20z. By then, clouds scatter to VFR-MVFR (perhaps still some straggling IFR along the south coast). Possible SCT SHRA/TS near/west of ORH after 20z Sat, although development and strength of any TS would depend on how quickly we see any breaks in OVC. If we do see any storms, they would likely be weakening as they move east of ORH. S/SW winds around 10-15 kt with occasional gusts to low 20s-kt range.

Saturday Night: High confidence.

Improvement toward SCT-BKN VFR with cold frontal passage, though some MVFR bases may develop overnight in western airports. Winds become W/WNW around 10-15 kt with gusts 25 kt (up to 30 kt high terrain).

KBOS TAF...High confidence in TAF thru 07z, then moderate to low.

VFR with E/SE winds continuing thru 03z before becoming S around 10 kt. Mainly MVFR bases with 3-6SM RA developing after 10z Sat, possibly IFR at times. RA ends ~18-20z with slow improvement in cigs to borderline VFR levels. Another round of showers and perhaps a rumble or two of thunder is possible late afternoon to early evening

KBDL TAF...High confidence in TAF thru 05z, then moderate to low.

VFR with south winds around 10 kt. MVFR-possible IFR bases with 3-6SM RA developing after 09z, then tapering off around early to mid afternoon. Possible SCT SHRA/TS after 20z depending on how quickly improvement develops from AM rains.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local MVFR possible. Strong winds with gusts up to 40 kt. Slight chance SHRA.

Sunday Night: VFR. Strong winds with gusts up to 40 kt. Slight chance SHRA.

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Slight chance SHRA.

Wednesday: VFR. Breezy.

MARINE
Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Southerly winds will be increasing to around 15-20 kt tonight, with seas building to 2-4 ft. Southerly flow then continues to strengthen into the SCA range for Saturday, with winds 25-30 kt and seas 4-7 ft. Rain and reduced visibilities expected until a sharp frontal passage Saturday evening, bringing a windshift to W/NW around 15-25 kt.

Outlook /Sunday through Wednesday/...

Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of rain showers.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain showers.

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Monday Night: Winds less than 25 kt.

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

Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 AM Saturday to 8 AM EDT Sunday for ANZ231>237-250-254>256.