Marine Weather Net

Montauk NY to Marthas Vineyard out 20 NM South of Block Island Marine Forecast


15 - 20


10 - 15




5 - 10

The Marine Weather Forecast In Detail:
ANZ256 Forecast Issued: 704 PM EDT Wed Jul 17 2024

Tonight...Sw Winds 15 To 20 Kt, Diminishing To 10 To 15 Kt After Midnight. Gusts Up To 25 Kt. Seas 5 To 7 Ft. Wave Detail: S 6 Ft At 8 Seconds. Isolated Tstms. A Chance Of Showers This Evening, Then Showers Likely After Midnight. Patchy Fog This Evening. Vsby 1 Nm Or Less, Increasing To 1 To 3 Nm After Midnight.
Thu...Sw Winds 10 To 15 Kt. Seas 5 To 7 Ft. Wave Detail: S 6 Ft At 8 Seconds. A Chance Of Showers In The Morning With Vsby 1 To 3 Nm.
Thu Night...W Winds Around 10 Kt, Becoming Nw After Midnight. Seas 4 To 6 Ft. Wave Detail: S 5 Ft At 8 Seconds.
Fri...N Winds 5 To 10 Kt, Becoming W In The Afternoon. Seas 3 To 5 Ft. Wave Detail: S 5 Ft At 8 Seconds.
Fri Night Through Sat Night...Sw Winds 10 To 15 Kt. Seas 2 To 4 Ft. Wave Detail: S 4 Ft At 8 Seconds And Sw 2 Ft At 3 Seconds.
Sun Through Mon Night...S Winds 5 To 10 Kt. Seas 2 To 3 Ft. Wave Detail: Sw 3 Ft At 6 Seconds. Winds And Seas Higher In And Near Tstms. Seas Are Reported As Significant Wave Height, Which Is The Average Of The Highest Third Of The Waves. Individual Wave Heights May Be More Than Twice The Significant Wave Height.
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Area Forecast Discussion
National Weather Service Boston/Norton MA
650pm EDT Wednesday July 17 2024

Scattered showers and thunderstorms will move across the region this evening before weakening. A cold front moves into the region Thursday bringing lower humidity away from the south coast. The front moves offshore Thursday night with high pressure in control Friday through the weekend. This brings seasonable temperatures and comfortable humidity levels.

Near Term - Until 6am Thursday Morning
650 PM

Bowing line segment moving through central MA with damaging wind the main threat. Best low level lapse rates across central and NE MA where highest risk of severe weather will be next 1-2 hours as line moves east into NE MA. Otherwise, expect a weakening trend this evening as boundary layer cools and CIN increases. However, still lots of convection upstream and expect additional scattered showers and isolated t-storms moving into the region overnight.

Previous discussion... * Severe Thunderstorm Watch for CT and interior MA north and west of I-95

Storms are increasing in coverage across eastern NY along a pre- frontal trough, and these storms will move west to east across interior MA and CT through early evening. Low and mid level lapse rates are muted but MLCAPES have increased to 1000 J/kg and further destabilization is likely so expect storms to intensify during the next few hours. Effective shear 35-40 kt which is more than sufficient for storms to organize into line segments and clusters. Damaging wind remains the primary threat, but latest CSU machine learning guidance is indicating there is a low prob for a tornado. Main focus for severe weather will be in the interior north and west of I-95.

Convection should weaken as it approaches RI and SE MA after 00z given more stable marine layer and diminishing instability. After midnight, another weak shortwave is forecast to track south of SNE coast and may result in regeneration of showers and embedded t- storms. Focus for convection overnight into Thu morning will be over the coastal waters but northern extent may reach along the south coast and Cape/Islands where instability lingers through the night. The uncertainty will be how far north showers and t-storms get.

Otherwise, cold front moves into northern and western MA toward daybreak with lows dropping into the 60s here, but lows holding in the low-mid 70s elsewhere with high humidity.

Short Term - 6am Thursday Morning Through Thursday Night
Thursday... A few showers and isolated t-storms may linger into the morning, especially SE MA and Cape/Islands ahead of the cold front where 70+ dewpoints contribute to marginal instability. The cold front is expected to eventually stall near the coastal plain which will keep humid conditions along the south coast, but gradually lowering dewpoints through the 60s and into the upper 50s further in the interior during the afternoon which will be a welcomed airmass change. Clouds will give way to increasing sunshine from NW to SE during the morning and into the afternoon with Cape Cod holding on to clouds the longest. Still can't rule out an isolated shower in the afternoon along the south coast where higher dewpoints pool. It will be warm day but less heat than the last several days. 925 mb temps 20-22C support highs in the mid-upper 80s but with lowering humidity, especially interior.

Thursday night... The cold front will finally move off the coast with light northerly flow bringing 50s dewpoints all the way to the south coast. Mainly clear skies expected with lows dropping into the mid-upper 50s across interior MA with low to mid 60s elsewhere.

Long Term - Friday Through Wednesday

* Dry and quiet weather late this week through the weekend. Near seasonable temperatures and comfortable humidity levels.

* Turning more unsettled early next week with increasing humidity.

Given the convective threat this afternoon and evening have not focused on extended term.

Friday through Sunday
Stuck under somewhat cyclonic flow through this timeframe with a deep trough over Ontario/Quebec and ridging over the Carolinas into the Mid Atlantic. High pressure dominates the weather through this timeframe. There are indications that a weak cold front slides in late on Sat into Sun.

Dry and quiet weather through this period. There are some indications that there could be spotty showers associated with the cold front that slides in late Sat into early Sun. Not enough model consensus to add at this point in time. For now NBM looks quite reasonable. High temps will generally be in the 80s, though there could be some low 90s across the Merrimack and CT Valley this weekend.

Monday through Tuesday... Flow turning more southwesterly during this timeframe in the upper levels with a similar set up. Will have cyclonic flow with trough over Quebec eastward and the ridge over the Carolinas/Mid Atlantic. Hints that could have one or two shortwaves riding the ridge, likely convective in nature, which could bring us more unsettled weather. Frontal boundary will be nearby/overhead.

Unsettled during this timeframe as flow turns more southwesterly, which will bring increasing moisture levels. Confidence quite low at this point given convective details are tricky to time out at this time range. For now the NBM slight chance to chances of precipitation suffice. Did bump up our thunderstorm chances as NBM seemed a bit low. High temps still in the 80s with increasing humidity levels.

Forecaster Confidence Levels:

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

Through Thursday night: High confidence.

Developing low level jet will bring an increase in SW winds over the south coastal waters into this evening with gusts to 25 kt. Winds diminish overnight into Thursday, then SW winds become NW then N Thu night behind the front. Seas will peak up to 7 ft over south coastal waters tonight with 5-6 ft seas lingering through Thu before slowly subsiding Thu night. Areas of fog redeveloping tonight over southern waters improving Thu afternoon. Showers and a few t-storms developing overnight into Thu morning, especially southern waters.

Rip Currents... A rip current statement is in effect into this evening and again Thursday along south coastal beaches due to high risk for rip currents. While winds diminish Thu, leftover 5-6 ft southerly swell will result in dangerous rip currents.

Outlook /Friday through Monday/... Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Friday Night through Monday: Winds less than 25 kt.

NOAA Boston MA Office: Watches - Warnings - Advisories
Heat Advisory until 8pm EDT this evening for CTZ002>004. MA...
Heat Advisory until 8pm EDT this evening for MAZ003>007- 010>021-026. High Risk for Rip Currents until 8pm EDT this evening for MAZ020>024. High Risk for Rip Currents from Thursday morning through Thursday evening for MAZ020-021-023-024. RI...
Heat Advisory until 8pm EDT this evening for RIZ001>007. High Risk for Rip Currents until 8pm EDT this evening for RIZ006>008. High Risk for Rip Currents from Thursday morning through Thursday evening for RIZ006>008.

Small Craft Advisory until 8am EDT Thursday for ANZ232. Small Craft Advisory until 8pm EDT Thursday for ANZ235-237- 254>256.