textproduct: Boston / Norton

WHAT HAS CHANGED

Added western Hampden County to the Heat Advisory, and issued rip current statements for south-facing beaches today through Wednesday with potential for dangerous rip currents and surf.

KEY MESSAGES

- Hazy, hot and humid today and Wednesday.

- Strong thunderstorms possible early overnight tonight and/or into Wednesday.

- Dangerous rip currents and surf expected on south-facing beaches today and Wednesday.

- More seasonable temperatures and less humid late week into the weekend, but still unsettled with chances for showers and thunderstorms, with the best chance this weekend.

DISCUSSION

KEY MESSAGE 1...Hazy, hot and humid today and Wednesday.

Main story today through Wednesday is the hot temperatures with some humidity with it, associated with a plume of 850 mb temperatures in the low 20s C range which begin to advect in today from the west- northwest. Heat Advisories remain in effect, as temperatures project to reach into the mid to upper 90s away from the Cape and the Islands today and end up slightly cooler on Wednesday. Certainly want to limit exposure outdoors today and Wednesday if possible; but this spell of heat should be a little different compared to the early-July oppressive heat and humidity we had. For one, both days feature pretty strong southwesterly breezes with peak gusts in the 25-30 mph range, and upwards of 35 mph towards the Cape and Islands which tend to blow pretty strongly on SW winds. Second, the southwest downsloped winds and some mixing should allow for dewpoints to stay in the mid to upper 60s: humid, but not the air- you-can-wear type oppressive humidity. Not sure it's fair to call it a dry heat, but compared to the early-July stretch, it could be construed that way. Thirdly, at least for today, the 00z HRRR-Smoke guidance progs a pretty sizable concentration of vertically- integrated smoke across a large part of the Northeast early this afternoon advecting in from the fires burning in northern MN and portions of central Canada. This smoke layer looks constrained to being aloft so no risk for health problems from it, but its possible that it could temper full sun to an extent with a hazier look to the sky if it's as concentrated as progged to be. For Wednesday, one of the bigger flies in the ointment at least for the northern portion of the Advisory is the timing of a cool front. Latest guidance shows this front now nearing the MA border by the pre-dawn hrs, then moving southward through the morning hrs to the MA Pike and to the southern coast later in the day. Could make the Advisory a bit borderline if we do get an early-day passage, as dewpoints tumble behind its passage. Heat indices today in the mid 90s to low 100s today, but could be closer to the low 90s north and mid/upper 90s south of the Pike Wednesday.

KEY MESSAGE 2...Strong thunderstorms possible early overnight tonight and/or into Wednesday.

This is the more uncertain element of the forecast the next couple days. Still looks as though northern New England has the greatest risk for severe weather today into part of tonight, with as much as a Enhanced (Level 3 of 5) risk for severe weather in northern ME, NH and VT. In Southern New England, we look capped to convection today and into part of tonight per bufkit sounding profiles, but there remains a large amount of instability above that capping inversion, in some solutions upwards of 2500-3000 J/kg of CAPE using an average parcel in the lowest 100 mb of atmosphere. Some of the high-res guidance is beginning to come around to the idea of showing convective development trailing back westward along a cold front with a weakening capping inversion into central VT/NH as soon as early overnight; but the timing and coverage of this activity still is pretty scattershot across the high-res suite. This could ultimately end up being a nowcast situation, but given this trend I couldn't really justify NBM's nil PoPs. Opted for up to 30% PoP along the MA/NH/VT border between 4-7 AM Wed, then slowly sagging southward through the day. If any storms develop, they would likely become strong to potentially severe quickly given the degree of instability aloft and pretty strong NW mid-level winds, with frequent lightning, hail and strong straight line winds all possible, potentially early in the day as well. Low confidence but potentially higher impact if storms can materialize.

KEY MESSAGE 3...Dangerous rip currents and surf expected on south- facing beaches today and Wednesday.

SW breezes expected today and again on Wednesday will end up building wave heights later today into tonight to around 5-8 ft on the outer waters, then start to lower into the 4-6 ft range for Wednesday but becoming longer in period. This poses a risk for dangerous rip currents and higher surf, and though it's often bullish in its output, it is supported by NWPS high probabilities for rip currents. Given the hot temperatures expected today and again on Wednesday, we should see an anticipated increase in people venturing to the beaches. For that reason we've hoisted a rip current statement for today and ran it through Wednesday early evening for the southern coastline, with those areas with south/southwest facing exposures most at-risk. There should be fewer numbers of people at beaches at night but since the waves look to be higher tonight, opted to not get cute with the timing. the Wave periods are on the shorter side today which could reduce wave energy to an extent, as it's often the longer period waves which cause the biggest risk for rip currents. Swim near vicinity of lifeguards and stay off jetties.

KEY MESSAGE 4...More seasonable temperatures and less humid late week into the weekend, but still unsettled with chances for showers and thunderstorms, with the best chance this weekend.

Upper low to our northeast drives a fast, but broadly cyclonic flow aloft into Southern New England most of this period. After the cool front moves southward into early Thursday morning, seasonable temperatures in the low to mid 80s return with less humidity. We'll have to watch for any ripple in the NW flow aloft thru late this week, which could trigger showers/storms, but too uncertain at this time. Ensembles continue to offer a wetter weather pattern evolving this weekend which offers the next best chance for needed rainfall.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Through 12z Tuesday: High confidence.

VFR. SW winds around 8-14 kt, strongest eastern/southeast MA.

Today: High confidence.

VFR. Hazy skies are possible due to high-altitude smoke lofted in from fires in central Canada, and messaged as BKN200 decks in TAFs. SW winds increase to around 12-16 kt with gusts 25-30 kt.

Tonight and Wednesday: Moderate confidence.

Mainly VFR outside of possible TSRA. Timing and coverage of storms is uncertain, but could develop in northern MA as soon as 07z Wed or further into Wed as cold front sags southward. Any storm could become strong if they do develop. SW winds continue tonight around 8-14 kt, but low-level shear is likely where gusts subside given 40-45 kt SW low level jet. Winds then shift to NW around 10 kt upon frontal passage, best estimate 13-21z from north to south.

KBOS Terminal...High confidence in TAF. VFR. Gusty SW winds to 30 kt today. Possible hazy skies this afternoon from smoke lofted aloft from Canadian wildfires.

KBDL Terminal...High confidence in TAF. VFR. Gusty SW winds to 25 kt today. Possible hazy skies this afternoon from smoke lofted aloft from Canadian wildfires.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: VFR.

Thursday through Thursday Night: VFR. Breezy.

Friday through Friday Night: VFR.

Saturday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday: High confidence.

SCAs take effect today and were extended into Wednesday. SW winds increase today to around 25-30 kt, with low prob of gusts to gale force near the Cape and Islands today into tonight, with seas building to 6-8 ft offshore by tonight. Seas then slowly ease into Wednesday but should still be in the SCA range for Wednesday. Potential for thunderstorms on the northern waters as soon as overnight tonight into early Wed AM, with lesser risk for thunderstorms on the southern waters Wed aftn/night.

Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

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

Saturday: Winds less than 25 kt. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Heat Advisory from 11 AM this morning to 8 PM EDT Wednesday for CTZ002>004. MA...Heat Advisory from 11 AM this morning to 8 PM EDT Wednesday for MAZ003>007-010>021-026. Heat Advisory from 11 AM this morning to 8 PM EDT this evening for MAZ009. Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for MAZ017>024. High Risk for Rip Currents from 10 AM EDT this morning through Wednesday evening for MAZ020>024. RI...Heat Advisory from 11 AM this morning to 8 PM EDT Wednesday for RIZ001>007. Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for RIZ001>008. High Risk for Rip Currents from 10 AM EDT this morning through Wednesday evening for RIZ006>008. MARINE...Small Craft Advisory from 4 PM this afternoon to 11 PM EDT this evening for ANZ230-231-250-251. Small Craft Advisory from noon today to 8 PM EDT Wednesday for ANZ232>235-237-254>256. Small Craft Advisory from noon today to 11 PM EDT this evening for ANZ236.