Narragansett Bay Marine Forecast (2024)

Synopsis
Mainly dry conditions expected into Thursday with below normal temperatures. The remnants of Debby will begin to approach Southern New England Thursday night into Friday, but make its closest approach to our north and west Friday evening into early Saturday. This will bring showers with pockets of heavy rainfall focused across the interior. That being said...it appears the threat for significant flooding has shifted west of the region. Dry and warm weather should arrive for most locations Saturday afternoon. The first half of next should feature very pleasant and mainly dry weather.

Near Term - Until 6am Thursday Morning
High pressure builds over Maine with surface ridging extending south into SNE will keep dry conditions across SNE tonight. Clouds will decrease this evening as drier air spills south, but may hang on to more clouds near the south coast as higher moisture axis remains along the coast. With any clearing, will have to watch for development of late night patchy radiation fog and stratus as winds will be light to calm. Lows will be mostly in the 50s, except lower 60s Cape/Islands.

Short Term - 6am Thursday Morning Through Thursday Night

Thursday... While surface ridging persists across SNE, column moisture will begin to increase from the south. Some of the global and hi-re guidance is suggesting a few showers may develop during the afternoon. This appears to be in response to a modest instability burst as reflected by increase in KI and lowering of SI values from SW to NE. Best chance of a few showers will be across western MA and northern CT where moisture is greatest, but much of the day will be dry. Otherwise, sunshine to start the day will give way increasing clouds. Highs will be in the 70s.

Thursday night... Backing flow aloft will result in tropical moisture plume ahead of Debby to spread northward into SNE as PWATs (Precipitable Waters) increase to around 2 inches. The increasing moisture combined with marginal elevated instability will lead to scattered showers developing and moving northward across the region. A few embedded t-storms are also possible. However, heavier rainfall will be confined well to the SW where best forcing assocd with remnants of Debby is located. Cloud cover and increasing dewpoints will result in a milder and more humid night with lows in the 60s.

Long Term - Friday Through Wednesday
Key Points... * Showers with heavy rainfall and a low risk for severe weather Fri into early Sat with the focus across interior southern New England

* Threat for Significant Flash Flooding & River Flooding continues to shift west of the region with the latest model guidance

* Dry & Warm weather may return for Sat afternoon

* Pleasant/Mainly dry weather for the first half of next week

Details... Friday into Early Saturday... Confidence continues to increase that the remnants of Debby will track further west and also faster than guidance depicted 36 hours ago. The remnants of Debby will lift rapidly northward across interior PA and NY State Fri/Fri night and then into northern New England/Quebec region Sat morning.

It is quite common for the main threat of significant flooding/heaviest rain to setup west of the track of tropical remnants. Given we are on the east side of the remnants and that it also picks up speed...the threat for Significant River Flooding and Flash Flooding has shifted west of the region. Still expect periods of showers with locally heavy rainfall Fri into early Sat...the focus of the heaviest rain should be Fri night into early Sat when the remnants pass closest to our region. The ECMWF/RGEM are on the heavier side indicating the potential for 2-3 inches of rain across parts of western MA/CT. This appears to be a result of some sort of secondary re- development near the Long Island/southern CT border. Meanwhile...the NAM/GFS (Global Forecast System) does not show this secondary feature as well with rainfall generally under 1-1.5 inches. Regardless...the threat for significant flooding appears to have shifted west of the region. If the higher amounts depicted by the ECMWF/RGEM occur...there might be some minor flooding issues but that appears to be the reasonable worst case scenario at this point.

We should also mention that we can not rule out a low risk of severe weather/brief tornado risk. This would mainly be late Fri into early Sat. Keep in mind this is a low probability as many mesoscale ingredients have to come together for severe weather. That being said...there is at least a low probability including a tornado risk. This is supported by the CSU Machine learning probs with our interior zones most at risk given they will be closest to the passage of the remnants.

Saturday Afternoon... Given the faster movement of Debby/s remnants...Sat afternoon looks to be mainly dry with sunshine emerging on southwest flow. A mild start and 850T near +16C should result in highs well into the 80s.

Sunday through Wednesday... Upper trough sets up across the northeast bringing very pleasant late summer weather to the region. Highs will be well into the 70s to the lower 80s with comfortable humidity levels for August standards. Overnight lows will be very pleasant in the 50s to the lower-middle 60s. Dry weather should dominate...but can not rule out a spot shower or two.

Marine
Forecaster Confidence Levels:

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

Tonight through Thursday night...High Confidence.

Lingering 5+ ft seas over southern waters will subside this evening, otherwise winds and seas will remain below SCA (Small Craft Advisory) thresholds through the period. E-NE winds 10-20 kt through Thu veering to SE Thu night.

Outlook /Friday through Monday/... Friday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.
Friday Night: Strong winds with gusts up to 30 kt. Rough seas up to 11 ft. Rain showers likely, slight chance of thunderstorms.

Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain showers.
Saturday Night: Winds less than 25 kt. Areas of rough seas.
Sunday through Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.

NOAA Boston MA Office: Watches - Warnings - Advisories
CT...None. MA...None. RI...None.

Marine
Small Craft Advisory until 10pm EDT this evening for ANZ254>256.