Marine Weather and Tide Forecast for East Sandwich, MA

NEAR TERM /UNTIL 6 PM THIS EVENING/

Key Points

* Heavy rain with localized flash flooding possible this morning into the early afternoon

* Isolated strong to severe thunderstorms possible across western MA and CT late this afternoon

A 500mb shortwave and surface low-pressure system will cross the region this morning. With strong lift from 850mb frontogenesis and PWATS approaching 2 inches, there will likely be very heavy rain this morning with localized flash flooding where stronger convection can develop. Opted to issue a flood watch this morning as HRRR 6hr PMM shows swaths of 2-4inches possible this morning across much of Eastern MA, CT, and much of RI. HRRR also shows moderate probs 30- 40% to exceed 10 year ARIs and low probs (5-10%) to exceed 100 year ARIs. Rain begins to taper off in the west to east today, lasting into the early evening hours across the Cape and Islands. If enough clearing can occur in western MA and CT, there could be some isolated strong to severe thunderstorms as roughly 500-100 J/kg of Cape builds. The best shear remains east of the instability axis, likely leading to pulse thunderstorms with the main threat being gusty winds. High temperatures stay in the 70s today with dewpoints around 70F as well.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/

Key Points

* Mainly dry with warm and humid conditions

* Low chance for a isolated strong to severe thunderstorm across western MA and CT

The low-pressure system moves offshore with rising heights and drier air aloft moving in for Friday. Unfortunately, the drier air aloft is unlikely to bring relief to the 70-degree dewpoints on Friday.
High temperatures warm in the 80s with heat indices approaching 90F.
Skies start mostly cloudy Friday, but clouds begin to scatter out in the afternoon, which could allow for a couple of isolated thunderstorms to form if it can overcome the subsidence aloft.
Again, the environment supports the possibility for pulse severe thunderstorms with instability nearing 1000 J/kg, but with less than 30 knots of shear.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/
Key Messages:

* Trending drier through the weekend * Summertime heat and humidity return early next week, with highs in the upper 80s to low 90s possible Monday through Wednesday * Daily chances for isolated, non-severe showers and thunderstorms

Saturday and Sunday

After a wet and unsettled week, we’ll begin transitioning to drier weather this weekend as an area of high pressure settles over the coastal waters to our east. This will support east/southeast flow through Sunday, resulting in relatively cooler temperatures (upper 70s to low 80s) east of I-495 along with sunny and dry conditions.

Across the interior, temperatures will be near normal, with daily highs in the mid to upper 80s. Elevated dewpoints in the upper 60s to low 70s will support diurnal instability west of I-495, leading to a slight chance of a pop-up afternoon shower or thunderstorm across the interior this weekend.

At this time, there are no signals indicating a risk for severe thunderstorms, as weak wind fields should suppress the wind shear needed to support deep moist convection. Any storms that do develop should collapse relatively quickly. Minimal, if any, thunderstorm activity is expected across eastern areas, as onshore flow/marine air should help stabilize the atmosphere.

Monday through Wednesday

Prevailing southwest flow returns on Monday, which will support rising temperatures across southern New England. Highs will reach the mid to upper 80s on Monday. A few scattered thunderstorms may also develop across the interior, as a pulse of shortwave energy could move through the Northeast Monday afternoon.

There is still no strong signal for the presence of deep-layer wind shear needed to support severe weather, but some uncertainty remains this far out.

By Tuesday, ensemble guidance suggests increasing heat, with a 40 to 50% chance of high temperatures exceeding 90 degrees across southern New England on both Tuesday and Wednesday. While there is no clear signal for widespread precipitation during the middle of next week, the typical slight chance for a diurnal thunderstorm remains possible.

Stay tuned for further details.

AVIATION /08Z THURSDAY THROUGH MONDAY/
Forecaster Confidence Levels...

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

06Z TAF Update...

Tonight...Moderate to high confidence.

IFR/LIFR for much of the region, with low end MVFR/IFR in the CT river valley. Showers and thunderstorms have already begun to move into western MA. These cells will be capable of producing very heavy rain with near zero visibility. Heaviest rain should end across western terminals around sunrise, while arriving in eastern terminals between 09-11z.

Thursday...Moderate confidence.

IFR/LIFR with moderate to heavy rain with some embedded thunder continuing across eastern terminals through 12-15z, 15-18z for the Cape and Islands. Lingering light rain likely continues past 18z in the east, meanwhile, western terminals could see isolated thunderstorms in the late afternoon, closer to 20-23z.
Unlikely cloud cover clears enough across eastern terminals for afternoon thunderstorms.

Thursday Night...

IFR/LIFR ceilings return with light/variable easterly. Some showers/storms possible along the south coast.

KBOS Terminal...High Confidence

Ceilings coming down to LIFR with onshore flow. Moderate to heavy rain with embedded thunder possible this morning through about 16z, then lighter rain and IFR CIGS for the remainder of the day. LIFR possible again tonight with onshore flow

KBDL Terminal... High Confidence

MVFR/IFR this morning with moderate to heavy showers and thunderstorms through about sunrise, then lingering light showers though the rest of the morning. Isolated thunderstorms possible this afternoon, mainly after 20-21z.

Outlook /Friday Night through Monday/...

Friday Night: VFR.

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

Saturday Night through Sunday: VFR.

Sunday Night: Mainly VFR, with local IFR possible. Slight chance SHRA.

Monday: Mainly VFR, with local MVFR possible. Chance SHRA, chance TSRA.

MARINE
Forecaster Confidence Levels...

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

Thursday to Thursday Night: Moderate confidence.

Strong thunderstorms crossing the waters this morning. Gusts of 40-50 knots possible with heavy rain and near zero visibility.
Rain continues for much of the day, tapering off this evening.
Low clouds and fog continue through tonight.

Winds 10-15 kts out of the SSE on the southern waters and out of the E to NE on the eastern waters. Winds closer to the shores along the south coast may be more NE. Seas 2-4 ft.

Outlook /Friday Night through Monday/...

Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES
CT...None.
MA...None.
RI...None.
MARINE...None.