textproduct: Boston / Norton

WHAT HAS CHANGED

A Slight risk (level 2/5) exists for the chance of thunderstorms Sunday night for western MA, including CT. Damaging winds are the primary risk. Otherwise, general trends remain unchanged.

KEY MESSAGES

- Dry with above normal temperatures continuing through the day Sunday.

- Showers and thunderstorms expected Sunday night.

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

- Seasonable temperatures and lower humidity returns through the first half of next week before a return to a more active pattern late-week.

DISCUSSION

KEY MESSAGE 1...Dry with above normal temperatures continuing through the day Sunday.

An unseasonably warm airmass remains overhead for southern New England for the rest of today into tomorrow, supporting above-normal temperatures with highs in the upper 80s and low 90s. Lows tonight will fall into the upper 50s/low 60s for most, with the coastal areas only falling to the upper 60s. However, drier conditions will persist with dewpoints down in the mid to upper 50s, so it will continue feeling not as uncomfortable as previous days. High pressure will remain affixed over the region for much of Sunday before the next system approaches in the evening hours.

KEY MESSAGE 2...Showers and thunderstorms expected Sunday night.

A cold front associated with an approaching shortwave disturbance will push through southern New England Sunday night will aid in increasing chances for showers and thunderstorms. Storms are expected to move through between 6-11 PM Sunday evening/night, and for western MA (into CT), a Slight (level 2/5) risk for severe weather has been raised. Latest guidance has more of an indication for an elevated convection setup towards the eastern slopes of the Berkshires down into Hartford, with the main risk being damaging winds. In terms of rainfall totals, there is still some uncertainty regarding where the heaviest rainfall will occur. Based on the latest guidance, there may be a "split" of higher totals that move just to the north and south of southern New England, but this could change depending on the development of a mesolow that could shift offshore heading into Monday morning. This would considerably limit rainfall amounts over southern New England. Currently, the region could expect totals ranging between 0.25-0.35" of rain and that low feature would be tracking more just off the coast of Maine. PWAT values are mainly forecast around 1.5" with pockets of 2.00"+ creeping north into RI, SE MA, and the Cape and Islands. Ensembles and deterministic members have continued trending this core of the moisture plume further north into these areas. 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, Sunday night and Monday night.

Astronomical tides will be building to their highest level for this month this weekend into Monday. The evening high tide periods both tonight, Sunday night 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 Sunday/Sunday night.

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). However given that there are more visitors to Southern New England who may not be as familiar with coastal flooding, we opted to issue Coastal Flood Statements for much of the southern and eastern coast with a Coastal Flood Advisory for Nantucket. These start tonight and run through Monday night.

KEY MESSAGE 4...Seasonable temperatures and lower humidity returns through the first half of next week before a return to a more active pattern late-week.

Cooler temperatures and lower dewpoints move into southern New england at the beginning of the work week.

Latest guidance shows 850 temps dropping below +10C most areas Monday and Tuesday. Dewpoints start to once again increase Wednesday, and global ensembles disagree about precipitation chances Wednesday with the GFS ensembles bringing precipitation chances back Wednesday during the daytime with the EC ENS holding off until Wednesday night if at all. Temperatures will start to climb again heading into Wednesday, but are still seasonable in the low to mid 80s with still tolerable humidity levels.

Unsettled weather continues Thursday into Friday as a stronger stronger disturbance aloft triggers more widespread shower/storm activity throughout southern New England. Specifics about timing and amounts still to be worked out, but 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 timeframe. Early indications showing a trend toward dryer weather to start next weekend.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

06z 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 storms to pass thorugh 00-06z west of ORH and roughly 06-10z 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.

Wednesday Night: Mainly VFR, with local MVFR possible. 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.

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

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.