textproduct: Boston / Norton

WHAT HAS CHANGED

Updated aviation section for 12Z TAFs.

KEY MESSAGES

- Pleasant weather for the Labor Day Holiday with low humidity and mild temperatures. The dry and pleasant conditions continue through Wednesday.

- Unsettled weather returns mid to late week but the threat for flooding and severe weather appear low at this time.

DISCUSSION

KEY MESSAGE 1...Pleasant weather for the Labor Day Holiday with low humidity and mild temperatures. Dangerous rip currents continue at east-facing beaches through most of the day. The dry and pleasant conditions continue through Wednesday.

4am Update: Went ahead and issued a Rip Current Statement for east-facing beaches as well as the islands. Numerous off and near-shore buoys are still reporting elevated wave periods of 8-10 seconds, which is favorable for the formation of rip currents and locally hazardous swimming conditions.

A tranquil Labor Day Holiday is on tap as high pressure builds over the Northeast. Aloft, these changes are driven by a broad 500 mb ridge sprawling from the mid south into the Northeast. Looking at a cool start to the morning after tonight's radiational cooling. The vast majority of locations will wake up to lows this morning in the lower to mid 50s with isolated 40s in favored valley locations. After a cool start, there's a lot to look forward to with regards to today's sensible weather. Temperature-wise it's a seasonably mild day with highs warming into the mid and upper 70s. To further solidify today as a peak weather day humidity levels will certainly be fall-like with dew points in the 40s and low 50s. Only caveat will be a somewhat gusty NW wind. A modest low-level jet of 25-30kts combined with a well-mixed boundary layer will yield gusts up to 20 mph. On Tuesday, the deeper mid-level trough continues to shift further eastward as a mid-level ridge continues to build in from the west. 925mb temperatures warm to +17-18C yielding high temperatures in the upper 70s with locations potentially hitting the 80 degree mark in the valleys. High pressure in place will support mainly dry conditions.

KEY MESSAGE 2...Unsettled weather returns mid to late week but the threat for flooding and severe weather appear low at this time.

By Wednesday, the mid-level ridge begins to break down and the pattern becomes more more zonal by Thursday. Guidance continues to show a series of shortwaves and low pressure systems passing N of the region with their associated frontal boundaries bringing chances for precipitation during the second half of the week. Any boundaries that pass through the region will be accompanied by a plume of above normal moisture, rising to 160-190% of normal by early Thursday yielding PWATS of 1.5" approaching 2.0". The positioning of an upper jet should supply ascent for periods of showers. There is spread across guidance in the finer details of the timing of the waves which will influence timing of the showers. A shortwave pushes through sometime Wednesday evening/night triggering the first round of showers which should taper off through the morning Thursday (at latest). The next wave moves through late Thursday/Thursday Night bringing another round of showers. With the timing of the waves still variable across guidance this leaves some uncertainty in thunderstorm/downpour potential. There will be plenty of moisture to support downpours; however, the timing of the wave would need be early enough to tap into the marginal instability build through the day for convection. For now, we are not seeing a strong signal for severe or flash flooding, more likely periods of showers with light accumulations outside of any isolated storms/downpours. An 850mb 35- 45kt LLJ shifts across southern New England into Thursday. There does raise a flag for potentially gustier winds; however, this will come down to how well we can mix down from 850mb or even 925mb. If things align, ensembles show potential for gusts in the 20-35 mph range on Thursday across the land and coastal waters. Still plenty of details to work out in the pattern before we come into better agreement about the gusts, but something to watch for now.

Temperatures Wednesday/Thursday lean near to slightly above normal with temperatures in the mid to upper 70s. A cold front pushes through early Friday bringing a cooler airmass this will support highs in the upper 60s low 70s.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Today and Tonight...High confidence.

VFR. NW winds increase to around 12 kt this morning with the chances for gusts up to 20 kt after 15z for most. Winds diminish this evening between 22-00z and become more WNW overnight.

Tuesday...High confidence.

VFR. NW winds around 5-10 kt. Chance for localized seabreezes towards the late afternoon hours around 20-21z. Will continue to monitor.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR.

Wednesday: VFR. Breezy.

Wednesday Night: VFR. Windy with local gusts up to 30 kt. Chance SHRA.

Thursday: VFR. Windy with areas of gusts up to 30 kt. Chance SHRA, slight chance TSRA.

Thursday Night: Mainly VFR, with local IFR possible. Breezy. Slight chance SHRA.

Friday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday: High confidence.

Generally light northerly winds this morning pick back up again today to around 15-20 kt, then subside overnight. Seas will continue to decrease to 3 ft or less through the day today. Lighter W winds Tuesday decrease to 10-15 kt with similar wave heights of 2-3 feet.

Outlook /Tuesday Night through Friday/...

Tuesday Night through Wednesday: Winds less than 25 kt.

Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of rain showers.

Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Slight chance of rain showers.

Thursday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents through this evening for MAZ007-014-015- 019-022>024. RI...None. MARINE...None.