textproduct: Boston / Norton

WHAT HAS CHANGED

Gale Watch has been issued for portions of the southern ocean waters Tuesday afternoon into Thursday.

KEY MESSAGES

- Light rain continues this afternoon into early Monday morning. Breezy, cloudy, and cooler Monday afternoon.

- Dry and cool through mid week. Watching the potential for a coastal low to form mid to late week, bringing chances for strong winds and rainfall heading into the weekend.

DISCUSSION

KEY MESSAGE 1...Light rain continues this afternoon into early Monday morning. Breezy, cloudy, and cooler Monday afternoon.

A raw, cool, and rainy afternoon continues across southern New England, with rain persisting through much of the evening. Rainfall will be predominantly stratiform with generally light to occasionally moderate rainfall rates. A rumble of thunder cannot be ruled out near the south coast, though the risk is quite low. Overall, additional rainfall amounts of 0.25-0.75 inch are expected, with some localized variability. Flooding is not a concern with this event. Rain gradually shifts offshore overnight, coming to an end by or before daybreak Monday. It remains raw and wet overnight, with lows in the upper 40s to lower 50s and a breezy northerly wind.

As for Monday, showers linger just offshore along a frontal boundary while 1030 mb high pressure builds in from the northwest. This results in a tightening pressure gradient and breezy north-northeast winds throughout the day, especially near the coast where gusts top out around 20-25 mph. Clouds hang tough for much of the day, though there may be a few glimmers of sunshine. It will remain cool, with highs ranging through the 60s. Clouds remain Monday night as well, with lows falling into the 40s across much of the region, while the urban centers remain in the lower 50s.

KEY MESSAGE 2...Dry and cool through mid week. Watching the potential for a coastal low to form mid to late week, bringing chances for strong winds and rainfall heading into the weekend.

Ensemble guidance remains in good agreement that an anomolously strong high pressure system will develop over Quebec Tuesday and linger into Wed/Thurs. This system likely keeps temperatures across New England cooler than normal, in the low to mid 60s, with a cooler airmass and several days of prolonged northeasterly flow. Despite the large areal coverage the Canadian high spans, guidance indicates the formation of a weak Tuesday across the Mid-Atlantic region that could push just far enough north into NJ to brush southern New England with spotty showers. Still some uncertainty in how far north that low could move, but general consensus in some low-end PoPs across the southern coast Tuesday... higher chances across southern CT, closer to NYC.

Both deterministic and ensemble guidance continue to indicate potential for a coastal low to form Wednesday into the later half of the week. While there is still a large amount of uncertainty in the forecast this time, the overarching trend has been the low slowly meanders north into the waters south of Nantucket; however, each model has this low taking a slightly different track: the GFS pushing further NE and closer to Nantucket, and the ECMWF further NW and closer to Long Island. Regardless, this system is likely to bring strong winds, rain, and the potential for erosion/coastal flooding.

Highest confidence at this time pertains to winds, especially over the waters. As the low deepens and approaches to the south, the Canadian high over Quebec is also likely to strengthen and expand, leading to a tighter pressure gradient over New England. Given there's still uncertainty in how strong the low and high get as well as the track of the low, there is still some question as to how strong the gradient will get. However, confidence is increasing in the potential for Gale Force winds across the southern waters, and a Gale Watch has been issued for Tuesday evening through at least Thursday morning. The latest ensemble guidance is also showing roughly 50 percent probabilities of Storm Force wind gusts across the ocean waters south of Long Island and Block Island as well as 20 to 30 percent probabilities of Storm Force gusts over Nantucket Sound and Cape Cod Bay as the low deepens Friday into Saturday. Winds over land along the south coast, Cape, and Islands throughout the week are more likely to be a touch slower than the marine winds, but still gusty... more on the order of 25-35 mph.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18Z TAF Update:

Through Tonight...High confidence in trends, moderate confidence in timing and ceilings.

MVFR to IFR with areas of -RA. The threat for LLWS has lessened, though it cannot be ruled out as a weaker low-level jet shifts across southern New England between 18z-06z. Otherwise, winds generally SE to ESE at 5-10 kt. Chances for embedded thunderstorms are very low to near zero. IFR ceilings become more widespread overnight, with localized LIFR possible. Visibilities generally 2- 5SM with -RA continuing overnight. -RA ends from west to east mainly between 06z-12z as winds shift to the N at 8-12 kt.

Monday...High confidence in trends, moderate confidence in timing and ceilings.

IFR/MVFR improving to VFR through the day, though exact timing remains somewhat uncertain. NNE to NE winds increase to 10-20 kt, with gusts up to 25 kt possible across the Cape and Islands, where sustained winds will also be strongest. Winds diminish somewhat heading into Monday night.

Monday Night...Moderate confidence.

VFR, though lower-end VFR ceilings are possible near the southern coast and Islands, potentially impacting terminals such as KACK. NNE winds 8-12 kt, increasing to 10-15 kt across the Cape and Islands.

KBOS Terminal...Moderate confidence in TAF.

Timing of IFR onset remains somewhat uncertain, but is generally expected after 21z. Have hinted at this potential with SCT groups at IFR levels for the time being, at least through 05z. IFR overnight, with ceilings improving between 10z-14z. NNE gusts up to 25 kt possible Monday afternoon.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night: VFR. Windy with gusts up to 30 kt.

Wednesday: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt.

Wednesday Night through Thursday: VFR. Strong winds with local gusts up to 40 kt.

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

Friday: Mainly VFR, with local MVFR possible. Strong winds with areas of gusts up to 45 kt. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Monday Night...High Confidence.

A low pressure system riding along a frontal boundary brings widespread rain to the waters this afternoon and evening. There is a low chance for a few rumbles of thunder, primarily across the southern waters. Rain ends early Monday morning, though a few showers could linger across the southern outer waters as the front sags south. Winds shift from E/SE to N/NE tonight as the front pushes south. Gusts increase with cold air advection Monday morning, which has prompted Small Craft headlines for all southern waters and Cape Cod Bay through Monday afternoon. Seas build to 3-5 ft, with the highest seas across the outer waters. Winds subside Monday evening, albeit briefly, ahead of another period of stronger winds Tuesday, for which a Gale Watch has been issued.

Outlook /Tuesday through Friday/...

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain showers.

Tuesday Night: Strong winds with gusts up to 35 kt. Rough seas up to 12 ft. Slight chance of rain showers.

Wednesday: Strong winds with gusts up to 35 kt. Rough seas up to 15 ft.

Wednesday Night through Thursday: Strong winds with gusts up to 40 kt. Rough seas up to 16 ft. Slight chance of rain showers.

Thursday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 16 ft. Chance of rain showers.

Friday: gale force winds with local gusts up to 45 kt. Rough seas up to 16 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Monday for ANZ231>235-237. Small Craft Advisory from 8 AM Monday to 3 AM EDT Tuesday for ANZ254>256. Gale Watch from Tuesday afternoon through Thursday afternoon for ANZ255-256-282-283.