textproduct: Boston / Norton

WHAT HAS CHANGED

Storm Watches have been put up over the waters for Friday and Saturday.

KEY MESSAGES

- Dry, cool, and breezy weather continues through Thursday.

- A strong coastal low pressure system will bring impacts to southern New England in the form of rain, rough seas, strong winds, and coastal flooding/erosion Friday into the weekend. Exact timing and magnitude of the winds and rain remain unknown.

DISCUSSION

KEY MESSAGE 1...Dry, cool, and breezy weather continues through Thursday.

More of the same over the next 48 hours as a sprawling high pressure continues to sit over eastern Canada maintaining cooler than average northeast flow over southern New England. High temperatures each day at expected to remain in the low 60s (east coast, closer to the onshore wind) to upper 60s (CT Valley). Normal highs for late September are 5-10 degrees warmer. As the pressure gradient tightens ahead of the approaching storms we'll continue to see those winds ramping up, gusting 25 to 35 mph both Wednesday and Thursday.

KEY MESSAGE 2...A strong coastal low pressure system will bring impacts to southern New England in the form of rain, rough seas, strong winds, and coastal flooding/erosion Friday into the weekend. Exact timing and magnitude of the winds and rain remain unknown.

Models continue to be consistent in indicating potential for a strong low pressure system to make its way up the eastern seaboard and eventually into the Northeast by Friday. Once here, detached from strong steering flow, the low becomes entrenched overhead, even retrograding back to the west for a time. This spells a prolonged period of wet and windy weather Friday through Sunday, though exact placement and magnitude of impacts remains uncertain. The latest ensemble probabilities continue to indicate the greatest rainfall potential (2+") over eastern MA and RI. The strongest winds will be over the waters where Storm Watches have been hoisted starting on Friday. On land the strongest winds will be along the coast and in the higher elevations. Wind headlines will likely be needed as ensemble guidance indicates >50% chance of gusts over 40 mph, even a 20-30% chance of gusts nearing 60 mph over Cape Cod and the islands. Specific impacts will come into focus as we learn the eventual track of the low. Timing of this early season nor'easter while trees still have all of their leaves will lead to a greater concern for wind damage to trees than if this were to happen late in the fall season.

Minor coastal flooding and significant coastal erosion is also a concern as we experience a prolonged period of gusty NE winds, combined with high astronomical tides. The greatest risk will be for eastern facing beaches, as early as the Friday afternoon's high tide for Nantucket, and as early as the Friday night high tide in Boston Harbor. Many locations will see several tide cycles of minor flooding well into the weekend. The low center lingers, weakening, Sunday before finally exiting east around Monday.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12Z update...

No significant changes from the previous update.

Today and Tonight...High confidence.

VFR. NE winds of 10 to 20 kt with gusts of 20 to 30 kt, strongest towards the southeast New England coast. Gusts near 35 kt for Nantucket.

Thursday...High confidence.

VFR, outside of MVFR cigs over ACK and some of the outer Cape. NE winds of 10 to 20 kt with gusts of 20 to 30 kt, strongest towards the southeast New England coast. Gusts near 35 kt for Nantucket.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

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

Friday: VFR. Strong winds with gusts up to 45 kt. Chance SHRA.

Friday Night: VFR. Strong winds with gusts up to 40 kt. Chance SHRA.

Saturday: VFR. Strong winds with gusts up to 40 kt. Chance SHRA, slight chance TSRA.

Saturday Night: Mainly VFR, with local MVFR possible. Strong winds with local gusts up to 40 kt. Chance SHRA, slight chance TSRA.

Sunday: Mainly VFR, with areas MVFR possible. Windy with gusts up to 35 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 Thursday...High Confidence.

NE winds 20-30 kt with gusts up to 35 kt at times Wednesday and Thursday as strong 1030+ mb high pressure over southeast Ontario moves eastward into Quebec. This northeast fetch will yield rough seas on the ocean waters, 6-12 ft. Dry weather and good visibility prevail.

Outlook /Thursday Night through Sunday/...

Thursday Night: Moderate risk for gale force winds with local gusts up to 45 kt. Rough seas up to 17 ft. Chance of rain showers.

Friday: gale force winds with gusts up to 45 kt. Rough seas up to 20 ft. Chance of rain showers.

Friday Night: gale force winds with gusts up to 45 kt. Rough seas up to 22 ft. Chance of rain showers, slight chance of thunderstorms.

Saturday: gale force winds with gusts up to 45 kt. Rough seas up to 21 ft. Rain showers likely, chance of thunderstorms.

Saturday Night: Strong winds with local gusts up to 45 kt. Rough seas up to 19 ft. Rain showers likely, slight chance of thunderstorms.

Sunday: Strong winds with gusts up to 35 kt. Rough seas up to 16 ft. Rain showers likely, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ230-236. Gale Warning from 8 AM Friday to 8 PM EDT Saturday for ANZ230- 236. Small Craft Advisory until 8 PM EDT this evening for ANZ231- 254. Gale Warning from 8 PM this evening to 8 AM EDT Friday for ANZ231-254. Storm Watch from Friday morning through Saturday evening for ANZ231-254-281. Gale Warning until 2 AM EDT Friday for ANZ232>235-237-255-256- 282-283. Storm Watch from late Thursday night through Saturday evening for ANZ232>235-237-255-256-282-283. Small Craft Advisory until 2 AM EDT Friday for ANZ250-251-280. Gale Warning from 2 AM to 11 AM EDT Friday for ANZ250-251-280. Storm Watch from Friday morning through Saturday evening for ANZ250-251-280. Gale Warning until 8 AM EDT Friday for ANZ281.