textproduct: Boston / Norton

WHAT HAS CHANGED

A Slight risk (level 2/5) remains this evening for the chance of thunderstorms across western MA, including CT, with damaging winds the primary risk. Otherwise, general trends remain unchanged.

KEY MESSAGES

- Hot and dry conditions linger today.

- Showers and thunderstorms expected tonight, some of which could have severe winds.

- High astronomical tides and up to one-foot of storm surge could cause minor coastal flooding for the evening high tides tonight Monday night.

- Seasonable temperatures and lower humidity return through the first half of the week with a more active pattern returning later in the week.

DISCUSSION

KEY MESSAGE 1... Hot and dry conditions linger today.

Temperatures remain in the low 90s (upper 80s along the southern coast, Cape, and Islands) today as an unseasonably warm airmass remains draped over New England. However, drier conditions will persist with dewpoints down in the mid to upper 50s. High pressure will remain over the region for most of today before the next system approaches later tonight.

KEY MESSAGE 2...Showers and thunderstorms expected tonight, some of which could have severe winds.

A cold front pushing into Southern New England tonight will bring an increase to shower and thunderstorm chances. Storms are expected to move through between 6-11 PM this evening/tonight, and for western MA (into CT), a Slight (level 2/5) risk for severe weather remains in effect, with the latest suite of guidance continuing to indicate the main risk of damaging winds across the eastern slopes of the Berkshires down into Hartford. Some guidance continues to indicate a split, where the most severe storms will push north and south of southern New England, but the latest trends have pushed that split further east, leaving higher confidence in severe storms across the western portion of the region. If this splitting feature occurs, rainfall totals will be limited. This morning's hi-res guidance has trended PWATs near 1.8" further north into northern CT and central MA, with pockets of 2.0"+ PWATs into RI, SE MA, and the Cape and Islands. With this surge of moisture, expecting rainfall totals ranging between 0.25-0.35" generally west of ORH, with localized areas in NW MA seeing neat 0.50". Considering the convective nature of these showers/storms, locally higher rainfall totals are not out of the question. These showers and storms should be clear of the region by ~7 AM Monday morning.

KEY MESSAGE 3...High astronomical tides and up to one-foot of storm surge could cause minor coastal flooding for the evening high tides tonight Monday night.

Astronomical tides will be peaking today into Monday. The evening high tide periods both tonight and Monday night pose the greatest risk as these high tides are the highest. Latest storm surge forecast data from P-ETSS and Stevens Institute indicate about a half to up to one foot of storm surge, peaking with tonight's high tide cycle.

This is a low-ceiling coastal flooding scenario, with splashover or at worst minor coastal flooding in the usual vulnerable shoreline roads (including but not limited to Easy Street in Nantucket and Morrissey Blvd in Boston). Given the influx of visitors to Southern New England who may not be as familiar with coastal flooding, we opted to continue Coastal Flood Statements for much of the southern and eastern coast with a Coastal Flood Advisory remaining in effect for Nantucket through Monday night.

KEY MESSAGE 4...Seasonable temperatures and lower humidity return through the first half of the week with a more active pattern returning later in the week.

A cooler and much drier airmass pushes into Southern New England Monday into Tuesday with latest guidance showing 850 mb temps dropping to near +10C. Highs are likely to drop into the low 80s, with dewpoints plummeting into the mid 40s to mid 50s, bringing about much more comfortable "feels like" temperatures. Temperatures will start to climb again heading into Wednesday, but are still seasonable in the low to mid 80s with still tolerable humidity levels. Long-range guidance continues to disagree regarding precipitation chances Wednesday, with the GFS (and ensembles) bringing precipitation chances back Wednesday during the daytime and the ECMWF (and ensembles) holding off until Thursday.

More active weather looks to develop around Thursday or Thursday night, as a stronger disturbance aloft moves in and sweeps a cold front through Southern New England. This could bring a better shot at showers/storms, although it's still too early for specifics at this time.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Sunday: High confidence.

VFR. SW winds increasing to 10-15 kt, with gusts to 25 kt.

Sunday Night: Moderate confidence.

Areas of MVFR to IFR possible with incoming SHRA and TSRA associated with a passing cold front. Expecting bulk of the showers and storms to pass thorugh 00-06z west of ORH and roughly 07-11z east of ORH. Winds prevailing out of the south from 10-15 kt sustained, shifting NW in the wake of the front. Gusts to 25 kt expected to continue through at least the first half of the nighttime period.

Monday: High confidence.

IFR conditions improve to VFR or high-end MVFR by 15z as the rain moves offshore. Generally NW winds decreasing to near 10 kts thorughout the day.

KBOS Terminal...High confidence in trends. Moderate confidence in timing. Expecting the rain to arrive by at least 07z, but could arrive as early as 05z. Could see some rumbles of thunder, but lower confidence in how far east lightning will travel.

KBDL Terminal...High confidence in trends. Moderate confidence in timing. Rain could arrive as early as 01z, but expecting arrival no later than 03z. Uncertain as to how widespread lightning will become, so included in PROB30.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Slight chance SHRA, slight chance TSRA.

Wednesday Night: VFR. Slight chance SHRA.

Thursday: VFR. Windy with local gusts up to 30 kt. Chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Through Sunday...High confidence.

Seas generally 1-3 ft, except 3-4 ft across the far outer waters through Sunday morning. Winds pick up from the S Sunday, sustained between 10-15 kt with gusts to 20 kt possible.

Sunday Night...High confidence.

Seas increase to 4-5 ft across the outer waters Sunday night into Monday, and winds pick up slightly, sustained between 15-20 kt and gusting to 25 kt. Winds also shift more W heading into Monday morning. Some showers and thunderstorms are a possibility during the overnight period over the waters, and localized gusts over 25 kt cannot be ruled out.

Monday....High confidence.

Seas remain 4-5 ft across the southern waters, but drop to 2-4 ft across the northern waters. Likewise, wind gusts remain around 20 kts across the southern waters and drop to near 10 kts across the northern waters.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt. Seas up to 5 ft.

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

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

Wednesday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

Wednesday Night: Winds less than 25 kt. Slight chance of rain showers, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Coastal Flood Advisory until 2 AM EDT Tuesday for MAZ024. RI...None. MARINE...Small Craft Advisory from noon today to 2 AM EDT Monday for ANZ230-236. Small Craft Advisory from noon today to 8 AM EDT Monday for ANZ231>235-237-250-251-254>256.