National Weather Service Boston/Norton MA
300am EDT Sat August 17 2024
Synopsis
Dry weather continues for the region today. A slow-moving front will lead to unsettled weather with showers and isolated thunderstorms Sunday evening through Monday night. A drying trend with seasonable temperatures are expected for the middle of next week. Meanwhile, Hurricane Ernesto will track well southeast of New England, but it will bring rough surf and strong rip currents to south-facing ocean beaches this weekend.
Near Term - Through Today
Widespread stratus trapped beneath a subsidence inversion to start today. Weak onshore flow may provide some brief breaks in this stratus towards the immediate east coast of MA. These lower clouds should dissipate later this morning, only to be replaced with some higher based clouds and smoke aloft. Thus, despite a high pressure moving overhead, expecting more clouds than sunshine today. All things considered, high temperatures should be slightly below normal, especially towards the east coast where light onshore flow will also help to keep temperatures lower.
The prime concern will be the arrival of long-period S to SE swells from distant Hurricane Ernesto. Headline for High Risk for Rip Currents for south-facing beaches along coastal RI, Cape and Islands continues. This is for the entire weekend. We may need to expand that to cover the coast of Cape Ann as well. In addition to the expected stronger rip currents, surf heigheights will be elevated. Those heading to the beaches this weekend need to heed the advice of local lifeguards and beach patrols.
Short Term - Tonight Through 6pm Sunday
Surface high pressure moves farther offshore tonight. A slow- moving front will try to move east, but have its progress delayed by the offshore high pressure. That said some showers may reach the western half of southern New England tonight, but are slightly more likely for Sunday. Could also see some isolated thunderstorms Sunday. Not looking for any significant rainfall however.
Near to slightly below normal temperatures continue.
Long Term - Sunday Night Through Friday
Highlights
* Widespread showers with embedded thunder for most of southern New England on Monday
* A few lingering showers into Tuesday followed by a cold frontal passage that will be followed by a cooler/drier air mass settling over The Northeast
* Dry/seasonable weather Wednesday through Friday with temperatures gradually increasing each day
Monday
An area of low-pressure associated with an upper-level trough at 500 hPa moves across southern New England on Monday. With sufficient moisture in place and PWATs (Precipitable Waters) near 1.5 inches, we're likely to receive widespread rainfall for much of the day Monday. This will be a modest rainfall event with accumulations ranging from 0.25 inches east of I-495 to 1.25 inches across western MA and CT. Latest model guidance suggests modest instability with the GFS (Global Forecast System) forecasting MLCAPE values between 500 and 1000 J/Kg so some embedded thunderstorms will be likely on Monday afternoon as well. Shear is also on the modest side with only 20 to 30 knots in the 0-6 km layer, so the risk for any severe thunderstorm development is low. However, some models are suggesting decent mid-level lapse rates in the 500 to 700 hPa layer near 6 C/km for portions of southern New England, so an isolated strong storm can't be ruled out at this point. CSU machine learning probs give most of the east CONUS including southern New England a 5 to 15 percent chance of severe weather on Monday. Timing of heaviest rainfall remains uncertain, but look for rain to affect the western areas during the first half of Monday followed by the eastern areas Monday afternoon into Monday evening.
Tuesday through Friday
A few showers may linger Monday night into Tuesday morning as a surface cold front associated with the aforementioned area of low- pressure pushes through the region. This will be accompanied by an early fall like air mass that will bring temperatures down to the upper 60s and low 70s on Tuesday. As skies clear Tuesday night into Wednesday, 925 temps near 10C and radiational cooling may allow for surface temps to fall as low as the upper 40s for select locations in interior southern New England.
High pressure begins to build in from the west on Wednesday supporting dry/seasonable conditions across the regions. Temperatures will be on the uptick between Wednesday and Friday with highs in the low 70s on Wednesday increasing to the upper 70s to low 80s by Friday. Overall looks like a quiet stretch of weather between the middle and end of next week.
Marine
Forecaster Confidence Levels:
Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent.
Overall high confidence in the forecast.
Although winds will be 15kt or less this weekend, Small Craft Advisories are in effect for the elevated wave heigheights due to the powerful swells coming in from the SE due to Hurricane Ernesto. The swells will also be of very long period (13 to 16 seconds), so this will also result in strong rip currents and high surf developing along south-facing coast lines. This may also result in rough conditions at the entrances to inlets and harbors.
Outlook /Sunday Night through Wednesday/... Sunday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain showers, isolated thunderstorms.
Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, isolated thunderstorms.
Monday Night through Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms.
Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.
Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...High Risk for Rip Currents from Sunday morning through Sunday evening for MAZ007. High Risk for Rip Currents through Sunday evening for MAZ022>024. RI...High Risk for Rip Currents through Sunday evening for RIZ006>008.
Marine
Small Craft Advisory from 10am this morning to 8pm EDT Sunday for ANZ235-237. Small Craft Advisory from 10am to 8pm EDT Sunday for ANZ250. Small Craft Advisory until 8pm EDT Sunday for ANZ254>256.
