textproduct: Boston / Norton

WHAT HAS CHANGED

Canceled the Heat Advisory for much of MA, leaving it in effect for northern CT, SE MA, and RI.

KEY MESSAGES

- Hazy, hot and humid Wednesday.

- Strong thunderstorms possible late tonight into Wednesday.

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

- Seasonable temperatures with less humidity for the second half of the week, though unsettled conditions with chances for showers and thunderstorms remain possible into this weekend.

DISCUSSION

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

Tweaked the Heat Advisory headlines today due to a layer of smoke aloft. This has been fairly opaque today, resulting in lower temperatures this afternoon. Even more smoke is projected for tomorrow, lowering confidence in reaching the Heat Advisory threshold for most of MA. That said, most people will still consider conditions to be at least warm and humid. Further adjustments may be needed with later forecasts.

KEY MESSAGE 2...Strong thunderstorms possible late tonight into Wednesday.

Strong convection over southeast Canada and northern New England may dive south into our region late tonight into Wednesday. Widely different answers in location and timing amongst the convection-allowing models. Most keep showers and thunderstorms out of southern New England. However, still thinking elevated CAPE values of 1,000-1,500 J/kg are possible late tonight into Wednesday. While this is likely not enough to result in severe weather, cannot completely dismiss the idea of a few thunderstorms, especially across northern MA.

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

SW breezes expected today and again on Wednesday will build wave heights 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.

For that reason we've hoisted a Rip Current Statement through early evening Wednesday 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...Seasonable temperatures with less humidity for the second half of the week, though unsettled conditions with chances for showers and thunderstorms remain possible into this weekend.

The upper level ridge that has been dominating the pattern for much of this week will start to slide more SE of the region for the second half of the week as an upper level trough with broad cyclonic flow to our north takes hold. A cold front passes through the region late Wednesday into early Thursday morning, which will help usher in more seasonable temperatures for the back half of the week. 925 mb temperatures fall to generally around 18-20C, which will be more supportive of high temperatures in the 80s. Thursday may be slightly warmer compared to later days due to breezy westerly winds and resultant downsloping, but drier air overall and lower temperatures aloft (as mentioned above) may only push highs into the low 90s. After that, expect 80s to persist into the start of next week.

Latest guidance is hinting at the possibility for a ripple in the NW flow aloft later in the week that could lead to more unsettled conditions. Guidance is also indicating a shift to more southerly flow for the weekend and a surge in PWAT values as a result. A surface low approaches from the west Saturday and with more of a NE track as currently indicated, its fronts would likely drag through the region and increase the risk for showers and thunderstorms through the weekend. Exact timing is still quite uncertain this far out, but ensembles and deterministic guidance suites remain favorable for a wetter end to the week, both on Saturday and Sunday.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

Tonight...High confidence.

VFR. Gusty SW winds may continue in some areas through tonight, namely BOS, HYA, and ACK. Elsewhere, winds are already starting to drop off a bit and will continue to do so heading into the overnight period. Areas of LLWS remain a possibility through the early nighttime hours tonight for terminals on the Cape and Islands due to a LLJ moving overhead of these terminals.

Wednesday...Moderate confidence.

Mainly VFR conditions throughout, however some visibility restrictions may be possible across western MA & CT due to increasing near surface smoke from Canadian wildfires. Additionally, tomorrow morning/afternoon some isol-sct showers may be possible for northern terminals, however no mention of VCSH/VCTS have been included at this time given the uncertainty in timing and coverage. A low probability for showers or storms returns in the afternoon as well, but confidence is once again too low regarding timing, location, and coverage for any that develop. Winds will become more W/NW around 10z, becoming gusty 20-25kt once again shortly after that.

Wednesday Night...High confidence.

VFR. Relatively light W to NW winds, going calm for some.

KBOS Terminal...Moderate Confidence. Minor visibility restrictions are possible on Wednesday due to concentrations of surface smoke from Canadian wildfires. Visibilities may drop to around 5-6SM.

KBDL Terminal...Moderate confidence. MVFR visibility restrictions are possible on Wednesday due to surface smoke from Canadian wildfires.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: VFR. Breezy.

Friday: VFR.

Friday Night: VFR. Slight chance SHRA.

Saturday: VFR. Breezy. Chance SHRA, chance TSRA.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy. SHRA likely, chance TSRA.

Sunday: VFR. Breezy. 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 Wednesday Night: 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 morning, with lesser risk for thunderstorms on the southern waters Wed aftn/night.

Outlook /Thursday through Sunday/...

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.

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

Saturday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers likely, chance of thunderstorms.

Sunday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Heat Advisory until 8 PM EDT Wednesday for CTZ002>004. MA...Heat Advisory until 8 PM EDT Wednesday for MAZ017>021. Air Quality Alert until 11 PM EDT this evening for MAZ017>024. High Risk for Rip Currents through Wednesday evening for MAZ020>024. RI...Heat Advisory until 8 PM EDT Wednesday for RIZ001>007. Air Quality Alert until 11 PM EDT this evening for RIZ001>008. High Risk for Rip Currents through Wednesday evening for RIZ006>008. MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ230- 231-236-250-251. Small Craft Advisory until 8 PM EDT Wednesday for ANZ232>235- 237-254>256.