textproduct: Boston / Norton

WHAT HAS CHANGED

High Wind Warning issued along the coast with a Wind Advisory issued for many locations further inland. Storm Warnings issued for all waters. Coastal Flood Watches for the eastern Massachusetts, Cape and Islands extended through Sunday.

KEY MESSAGES

- Strong/long duration Nor'easter will bring strong to damaging wind gusts, coastal flooding/beach erosion, and periods of heavy rain late Fri through the weekend. Power outages are a concern particularly along the coast with fully leafed trees.

DISCUSSION

KEY MESSAGE 1...Strong/long duration Nor'easter will bring strong to damaging wind gusts, coastal flooding/beach erosion, and periods of heavy rain late Fri through the weekend. Power outages are a concern particularly along the coast with fully leafed trees.

An early season/long duration Nor'easter will bring a variety of impactful weather to southern New England later Fri right through the weekend. While there remains some uncertainty on the exact track and where the worst of the impacts are felt...confidence is relatively high that this will be an impactful storm for our region.

There are several moving parts that our ideal for a strong early season Nor'easter. The high pressure over Quebec and the offshore low pressure system are both indicated to be outside the EPS/GEFS models climatology. This will result in a strong persistent NE gradient of wind beginning Fri and continuing into Sunday. While there remain track differences...the low pressure system initially backs westward to a position somewhere south of Long Island before eventually lifting NE and gradually weakening through early next week. This is the reason that this storm will be of such long duration. The easterly LLJ is also shown to be outside the models climatology. This will not only result in the forcing for bands of rain moving across the region...But several impacts that we will break down below.

1) Strong to Damaging Wind Gusts...

The biggest concern with the strong NE winds are that they will be of both long duration and also coupled with heavy rain/fully leafed trees. This will exacerbate the risk for tree damage and power outages than if this same storm were occurring a few months later. The strongest of the winds will be along the coast...where we expect NE wind gust of 45 to 60 mph. It is also possible a few spots see winds reach 65-70 mph across the Islands...but that will be dependent on the track. Regardless...whether or not places hit specific high wind criteria is less important that the long duration combined with the fully leafed trees. Given that factor...we opted to go with High Wind Warnings along the coast. Further inland...we are expecting NE wind gusts of 30 to 45 mph but a few gusts near 50 mph are possible in heavier bands of rain. Again...given the fully leafed trees combined with long duration of the event opted to issue a Wind Advisory. The wind and tree damage/power outage risk will be the biggest impact for most people.

2) Beach Erosion/Coastal Flooding...

The other big issue with this storm will be the expected beach erosion/coastal flooding issues over multiple high tide cycles. While this will not be a storm under-going rapid bombogenesis...but the persistence of these strong NE winds and high seas offshore are concerning. A storm surge on the order of 1 to 2 feet and perhaps briefly near 2.5 feet are expected late Fri right through the weekend along east face ocean exposed beaches. We extended the Coastal Flood Watch in these locations through Sunday. This along with 15 to 25 foot seas offshore will result in pockets of minor coastal flooding/beach erosion during each high tide cycle late Fri through the weekend and a few pockets of low end moderate coastal flooding are also possible. Astronomical high tides are increasing through the weekend...so even as winds eventually start to slowly diminish these issues will be a concern. Given this event will impact multiple high tide cycles...the water may struggle to drain out after each high tide. Heavy rainfall may also exacerbate these issues a well. Overall...the biggest impact from this system may be in regards to beach erosion given such a long duration event.

While NE winds will result in less coastal flood impacts on the south coast...high seas just offshore and swell may result in some splashover/minor coastal flooding in these locations as well. This is something we will need to watch.

3) Heavy Rain and Timing...

Lastly...periods of heavy rain will be impacting the region at times later Fri into the weekend. This is one area where there remains some significant differences on how quickly the rain shield overspreads the region from southeast to the northwest. The GFS/RGEM are on the faster side with rain ovespreading most of the region later Fri into Fri night. Meanwhile...the ECMWF/NAM struggle to bring steady rain into much of the interior until Sat. We blended the differences for now...but once the rain arrives will basically continue through the weekend and even into Mon. Rainfall totals of 1- 4" are possible with the highest amounts most likely near the coast. We opted not to issue a Flood Watch given some of the model guidance takes the heaviest rain south of our region and given the fact that its over a long duration.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

00z TAF Update...

Through Tonight...High confidence.

VFR, outside of some areas of MVFR cigs over portions of southeast MA, especially towards ACK and the Cape tonight. Cigs there may periodically break to VFR, though the lingering low clouds may stick around through much of tonight. NE winds of 10 to 20 kt with gusts of 20 to 30 kt, strongest towards the southeast New England coast. Gusts near 40 kt for Nantucket.

Friday...High confidence.

VFR most of the day, with MVFR cigs moving in from the southeast, impacting ACK as early as 14z and FMH/HYA by 20z. Lowered cigs come following -RA/RA moving in throughout the day from SE to NW. Strong NE winds, 15-25 kts with gusts 30-45 kts, strongest over southeast MA terminals.

Friday Night...High confidence in trends. Moderate confidence in timing.

MVFR further overspreads the region from SE to NW. Local IFR possible towards the Cape and Islands late. Strong NE winds continue and increase in intensity, generally sustained between 10-20 kt inland and 25-35 kt towards SE MA, Cape Cod, and the Islands. Gusts to 55 kt are possible for this area as well, with gusts to 35-40 kt possible over the interior.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday: Mainly MVFR, with local IFR possible. Strong winds with gusts up to 55 kt. RA.

Saturday Night: MVFR/IFR conditions possible. Strong winds with gusts up to 50 kt. RA.

Sunday: MVFR/IFR conditions possible. Strong winds with gusts up to 45 kt. RA.

Sunday Night: Mainly VFR, with local IFR possible. Windy with gusts up to 35 kt. SHRA, slight chance TSRA.

Monday: Mainly VFR, with local MVFR possible. Windy with local gusts up to 30 kt. SHRA likely, slight chance TSRA.

Monday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA.

Tuesday: Mainly VFR, with local MVFR possible.

MARINE

Forecaster Confidence Levels...

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

Tonight through the Weekend...High confidence.

* Dangerous conditions for Mariners Fri into the weekend with NE wind gusts of 45 to 60 knots and seas offshore of 15-25 feet.

An early season Nor'easter will combined with high pressure over Quebec to result in strong NE wind gusts of 45-60 knots and seas offshore building to between 15 and 25 feet late Fri into the weekend. Storm Warnings have been issued for all waters. This is a dangerous storm for mariners with the worst conditions later Fri into Sun. Mariners should consider returning to port as soon as possible. NE winds will persist Mon too...so although conditions will improve this process will be quite slow.

Outlook /Saturday through Tuesday/...

Saturday: Moderate risk for storm force winds with gusts up to 60 kt. Rough seas up to 25 ft. Rain.

Saturday Night: Low risk for storm force winds with gusts up to 50 kt. Rough seas up to 22 ft. Rain.

Sunday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 14 ft. Rain.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 14 ft. Rain showers likely, slight chance of thunderstorms.

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

Monday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...Wind Advisory from noon Friday to 2 AM EDT Sunday for CTZ002>004. MA...Wind Advisory from noon Friday to 2 AM EDT Sunday for MAZ004- 011-026. Wind Advisory from 8 AM Friday to 2 AM EDT Sunday for MAZ005- 006-012>014-017-018. High Surf Advisory from 5 AM Friday to 8 PM EDT Sunday for MAZ007-015-016-019-022>024. High Wind Warning from 8 AM Friday to 2 AM EDT Sunday for MAZ007-015-016-019>024. Coastal Flood Watch from Friday afternoon through Sunday evening for MAZ007-015-016-019-022>024. RI...Wind Advisory from 8 AM Friday to 2 AM EDT Sunday for RIZ001. High Wind Warning from 8 AM Friday to 2 AM EDT Sunday for RIZ002>008. MARINE...Storm Warning from 2 PM Friday to 8 PM EDT Saturday for ANZ230- 236. Storm Warning from 8 AM Friday to 8 PM EDT Saturday for ANZ231- 254-281. Storm Warning from 2 AM Friday to 8 PM EDT Saturday for ANZ232>235-237-255-256-282-283. Storm Warning from 11 AM Friday to 8 PM EDT Saturday for ANZ250-251-280.