Narragansett Bay Marine Forecast (2024)

Synopsis
A period of mainly dry weather for southern New England today, before scattered showers and thunderstorms develop late in the day. Another round of showers and thunderstorms is expected Sunday. The stronger storms this weekend will contain torrential downpours and gusty winds. It remains very warm and humid, especially Saturday. Dry for much of Monday, but a cold front will bring scattered showers and thunderstorms during the afternoon. A few stronger storms cannot be ruled out. Cooler after Monday, but the pattern remains active for much of the upcoming week with a frontal boundary stalled nearby or overhead.

Near Term - Until 6pm This Evening
725 AM

Forecast remains on track. No adjustments in the latest update.

415 AM

* Another hot and humid day with heat indices 95-104 * Mainly dry weather, then risk of storms after 4 pm

Weak short wave moving across northern New England early this morning and triggering scattered showers and thunderstorms along the MA/NH border northward. This activity will exit NE into Maine with weak short wave ridging, associated subsidence and some column drying develops in its wake across SNE later this morning and afternoon afternoon. Thus, a period of dry weather today along with morning clouds giving way to sunshine. Still a very warm airmass over the region with temps aloft +23C at 925 mb and +18C at 850 mb. These temps aloft combined with mixing to around 850 mb, supports highs from the upper 80s across the high terrain, to low 90s across most of the region, with low to mid 80s along south coastal beaches of MA and RI. These temps combined with tropical dew pts in the low to mid 70s, will yield dangerous heat indices from 95 to 104 across much of the region, including Boston, New Bedford, Fall River, Providence and Hartford. Thus, heat advisory remains posted. SW winds 10-15 mph, with gusts up to 20 mph over southeast MA will provide some minor relief.

This excessive heat and humidity will yield moderate instability once again, with CAPEs (Convective Available Potential Energy - high values indicate potential for severe weather) 1500-2000 j/kg. However, forcing for ascent does arrive until after 20z across CT into western-central MA. This instability combined with steep low level lapse rates up to 9C/KM, coupled with PWATs (Precipitable Waters) climbing to 2 inches and dew pts in the low to mid 70s, supports a low risk of wet microburst. Nadocast and CSU machine learning probservations indicate greatest risk will be across CT into western-central MA after 20z/4PM. The remainder of the region will remain mainly dry, with convection likely holding off until 00z/8pm and thereafter.

Short Term - 6pm This Evening Through 6pm Sunday

415 AM

* Another round of scattered showers/thunderstorms Sunday, with a few strong to severe storms possible

* Not as hot Sunday, but remaining very humid

Saturday night... Short wave energy continues to advect across the region. This increases deep layer shear up to 30 kt and combined with high dew pts yielding some instability, scattered showers and isolated thunderstorms are expected to traverses the entire region. A few strong storms are possible this evening up to about 03z. Environment favors wet microburst storms. Remaining warm and humid tonight, with lows in the upper 60s to lower 70s, mid 70s for the urban areas of Boston. Given high dew pt airmass continues, patchy fog is possible.

Sunday... Short wave trough moves across the region, yielding deep layer shear up to 30 kts along with moderate instability with CAPEs up to 1500 j/kg. Hence, modest shear and CAPE profiles will support the risk for a few strong to severe storms, with potentially damaging winds. This is supported by CSU machine learning wind probs. Tropical airmass remains in place with PWATs (Precipitable Waters) up to 2 inches and dew pts in the 70s, supporting localized flash flood threat.

Otherwise, very warm and humid conditions continue. Not as hot as previous days, with highs in the low to mid 80s. However, with dew pts in the 70s, it will remain very uncomfortable with heat indices in the low 90s. Southwest winds 10-15 mph with gusts up to 25 mph across Cape Cod and the Islands.

Long Term - Sunday Night Through Friday
415 PM

Highlights

* Dry for much of Monday, but cannot rule out hit or miss showers/storms during the afternoon. A few strong storms are possible. Oppressive heat and humidity.

* Unsettled on Tuesday as a frontal boundary slides in.

* Forecast confidence drops significantly mid to late in the week as the front may still be nearby/overhead. Thus, could still be unsettled and will need to keep an eye on a potential tropical cyclone traveling up the east coast.

Monday... Beginning of a pattern change. Initially will have a shortwave over southern New England late on Sun. The shortwave lifts offshore by by early on Mon. Flow turns more cyclonic and quasi zonal for the rest of Mon. A shortwave digs into southern Quebec by late in the day. High pressure nudges in early on Mon, but a cold front will approach from the NW late in the day.

Could have a few lingering showers/storms before sunrise across portions of the south coast before sunrise. Overall expect dry weather to prevail for much of the day. Though will have increasing chances for showers and thunderstorms during the afternoon and heading into the evening. Will need to keep an eye on this period as there are signals that we could have some strong to perhaps severe thunderstorms. Ahead of the front will have a few hundred to roughly 2000 J/kg of MUCAPE and deep layer shear in the 0-6 km layer increasing to 30-40 kts. The big questions are we are quite removed from the upper forcing (and questions on timing the cold front) and given the S/WSW flow will have some downsloping. This results in slightly drier dewpoints and warmer temperatures. Mid level lapse rates are around 6 degrees Celsius and low level lapse rates are nearly adiabatic. Based on the environment think that a few strong/severe storms cannot be ruled out. This is supported by latest CSU ML guidance, which shows a 15-30 percent probs of strong/damaging winds and low probs (5-15 percent) for severe hail.

Did bump up our temps and lowered our dewpoints due to the downsloping anticipated. Should result in another day of oppressive heat with highs solidly in the 80s with some low 90 degree readings across the Merrimack and CT River Valley. Should see dewpoints in the 60s for most other than the immediate south coast where they are in the lower 70s. The end result are heat indices ranging from 85-95 degrees.

Tuesday... Cyclonic quasi-zonal flow in place through this timeframe. Fast moving shortwave sliding across the Great Lakes region on Tue. Some uncertainty on the exact timing this wave slides into and through our region. The cold front previously mentioned will slowly slide into and perhaps through much of southern New England.

Main change in the latest update was to increase precipitation chances from the default NBM through this timeframe, but especially during the afternoon hours. Should have a southwesterly (15-30 kt) low level jet impinging on the region as the front is sliding in. This will likely bring rain showers for much of southern New England, but the best shot will be along the immediate south coast. The big question will be where the frontal boundary stalls/sets up as at this point we appear to be on the cool side of the front, so there is not much instability to work with. Should have PWATs (Precipitable Waters) of 1.75 to 2+ inches, which is around 1-2 STD above model climo per NAEFS/EPS. Still have decent warm cloud layer depths of 3-4 km, so warm rain processes may be efficient. Think the stalled out front in combination with the moisture and LLJ could result in some training storms, so flooding potentially a risk. This matches up well with WPC latest Day 3/4 ERO.

With the cold front finally through much of southern New England will see a cooler airmass in place. NBM generally looked reasonable so have kept the temps generally in the 70s.

Mid to late in the week... Considerable uncertainty during this timeframe with a front stalled nearby or over us. This may interact with the tropical system lifting from the Southeastern US. There are still significant differences with the exact timing and track of the tropical system, along with little run-to-run consistency. Due to this have stuck with the NBM. Could have a heavy rain risk, especially if front remains overhead and we tap into the tropical moisture. The EPS is showing PWATs (Precipitable Waters) of 1-1.5 STD above model climo whereas the NAEFS is more muted through this period. Something we will need to monitor as we get closer to this timeframe.

Marine
Forecaster Confidence Levels:

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

415 AM

Today through Sunday... Persist SW winds 10-15 kt, with winds increasing up to 20-25 kt Sunday afternoon. This combined with long SW fetch, SCA (Small Craft Advisory) remains posted for building seas and increasing winds tonight and Sunday. Late night/early morning fog expected, but improves by late morning into the afternoon each day. Scattered thunderstorms late Sat, Sat evening, then again Sunday afternoon/early evening.

Outlook /Sunday Night through Wednesday/... Sunday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain showers.
Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.
Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms.

Tuesday Night through Wednesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely, isolated thunderstorms.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...
Heat Advisory until 7pm EDT this evening for CTZ002>004. MA...
Heat Advisory until 7pm EDT this evening for MAZ005>007- 011>021. RI...
Heat Advisory until 7pm EDT this evening for RIZ001>004.

Marine
Small Craft Advisory from 6pm this evening to 8pm EDT Sunday for ANZ254>256.