textproduct: Boston / Norton

WHAT HAS CHANGED

Gale watches have been expanded and upgraded to Gale Warnings. Small craft advisories have also been issued for our northern waters today into Thursday. Confidence in an impactful coastal storm for Friday into the weekend is increasing.

KEY MESSAGES

- Dry, cool, and breezy conditions continue through Thursday.

- Probabilities are increasing for a strong coastal low pressure system to bring impacts to southern New England in the form of rain, rough seas, strong winds, and coastal erosion late week into the weekend.

DISCUSSION

KEY MESSAGE 1...Dry, cool, and breezy conditions continue through Thursday.

Over the next several days southern New England will see a persistence forecast without much change. Basically, cooler than average temperatures under persistent northeast flow will be the story of the week thanks to our placement south of a broad area of high pressure over eastern Canada. As this high pressure continues to sit and even expand, a coastal low pressure system will slowly be meandering up the eastern seaboard. While this will likely bring more direct impacts to the region at the end of the week, we'll begin to feel the impacts of the ever tightening pressure gradient as early as Tuesday. Those breezy northeast winds will be even moreso on Wednesday. While the strongest gusts will be over the waters where Gale Warnings are in effect, locations along the coast and especially the Cape and Islands are increasingly likely to see wind gusts 25 to 35 mph each day through Thursday. This, while high temperatures struggle to get out of the low 60s so together it will feel much cooler than the normal low 70s we'd expect this time of year.

KEY MESSAGE 2...Probabilities are increasing for a strong coastal low pressure system to bring impacts to southern New England in the form of rain, rough seas, strong winds, and coastal erosion late week into the weekend.

Thursday onward is where uncertainty ramps up considerably, owing to the significant spread amongst the guidance as to how this coastal low evolves in its track up the coast. That being said, the last few runs of GFS guidance have trended toward the ECMWF solution showing a retrograding back to the west, meandering with little forward motion through the weekend. Of course, this is only one deterministic run, but it is so far a trend for a few run and GEFS ensemble guidance has also evolved to show a stronger, more western low track with the 00z run. Should this be the solution that pans out, there's a good chance we'll be dealing with storm force wind gusts on the waters and wind advisory conditions at least for coastal locations by Friday. Additionally, the many days of persistent and increasing NE flow will lead to high seas and potential for significant coastal erosion on the east coast, especially given astronomically high tides. It doesn't appear that the low is likely to finally exit east until at least early next week but again, confidence in specifics is low Friday onward.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Today...High confidence.

VFR after any marginal MVFR cigs depart the coastal plain by mid to late morning. NE winds 7-15 knots with gusts along the coastal plain of 20 to 25 knots.

Tonight...High confidence.

Mainly VFR. NE winds of 5 to 15 knots tonight with 20-25 knot gusts at times across the southeast New England coast and 25-30 knots for Nantucket.

Wednesday...High confidence.

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

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR. Windy with gusts up to 35 kt.

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

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

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

Friday Night through Saturday: Mainly VFR, with local MVFR possible. Strong winds with gusts up to 45 kt. SHRA likely.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday Night...High Confidence.

NE winds 15-20 kt with gusts up to 25 kt at times will continue, as strong 1030+ mb high pressure over southeast Ontario moves eastward into Quebec. This northeast fetch will yield rough seas on the ocean waters. Dry weather and good vsby prevail. Potential for gale force gusts appear to hold off until Wed and beyond. Seas 4-7 ft on Tuesday increase to 6-13ft by Wednesday and Wednesday night.

Outlook /Wednesday Night through Saturday/...

Thursday: Moderate risk for gale force winds with areas of gusts up to 45 kt. Rough seas up to 15 ft. Slight chance of rain showers.

Thursday Night: gale force winds with areas of 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 19 ft. Rain showers likely. Local visibility 1 to 3 nm.

Friday Night through Saturday: gale force winds with gusts up to 45 kt. Rough seas up to 20 ft. Rain showers likely, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents through this evening for MAZ007-015-016- 019>024. RI...High Risk for Rip Currents through this evening for RIZ002-004>008. MARINE...Small Craft Advisory until 8 PM EDT Thursday for ANZ230-250- 251. Gale Warning from 8 PM Wednesday to 8 PM EDT Thursday for ANZ231-254. Gale Warning from 5 AM Wednesday to 8 PM EDT Thursday for ANZ232>235-237-281. Small Craft Advisory from 5 AM Wednesday to 8 PM EDT Thursday for ANZ236. Gale Warning from 2 AM Wednesday to 8 PM EDT Thursday for ANZ255-256-282-283.