Penobscot Bay Marine Forecast (2025)

Synopsis
High pressure near the Gulf of Maine will maintain onshore flow and mostly dry conditions through the weekend. A frontal system approaches late Sunday and crosses the area Monday into Tuesday bringing the next chance for widespread rainfall. Meanwhile, Hurricane Ernesto will be tracking north through the western Atlantic and staying well out to sea. Long period swell from Ernesto will start to arrive tonight and peak around Monday bringing high surf and a rip current risk. High pressure then builds in around the middle of next week.

Near Term - Until 6pm This Evening
630 AMOnly minor edits were made to reflect observational trends.

Previously... The persistent upper low in the Canadian Maritimes will lift out into the Atlantic today with a mid level ridge axis sliding across the forecast area. At the surface, an area of high pressure is centered over southern Nova Scotia and will slowly drift east through the day. Moist onshore flow beneath an inversion has led to widespread low clouds and areas of fog to develop early this morning. While deep layer ridging will keep the forecast area mostly dry today, mesoscale models suggest low clouds will be stubborn to scatter out this morning. As low clouds do scatter out late this morning some mid to high level clouds associated with a trough to the west of New England will start to spill into the area. Additionally, there will still be some wildfire smoke aloft over the area, but this smoke will eventually pull east of the area as the upper low moves into the Atlantic. This will lead to some filtered sunshine this afternoon after a mostly cloudy start to the day.

Long period swell from well offshore Hurricane Ernesto will start to enter the Gulf of Maine later today, although the greatest swell will not arrive until late Sunday and Monday. Nevertheless, there will be an increasing rip current risk late today as the swell first approaches the Mid Coast. Highs today will generally be in the mid 70s along the coastal plain. Highs increase farther inland to the upper 70s across the north and low 80s along the CT Valley away from the marine influence.

Short Term - 6pm This Evening Through 6pm Sunday
A trough over the Great Lakes will slowly slide east tonight with high pressure offshore providing moist onshore flow again tonight. This will bring low clouds and potential for fog along the coastal plain with chances for showers increasing west to east towards day break Sunday. Lows tonight will generally be in the upper 50s to low 60s.

The 00Z model suite suggests the trough over the Great Lakes makes little progress eastward Sunday as Ernesto tracks north through the western Atlantic. This will keep the best forcing for ascent to the west of the area and have generally kept slight chance to low chance PoPs (15 to 30 percent) in the forecast. High pressure offshore will maintain onshore flow with highs slightly cooler than today. Long period swell from Ernesto will still be on the increase approaching 5 feet at 15 seconds towards the Mid Coast first then spreading towards southern beaches late Sunday. Have gone with a High Surf Advisory first starting along the Mid Coast to coastal Cumberland County starting early Sunday morning with the High Surf Advisory not going into affect for areas south of Cape Elizabeth until late Sunday. High Surf Advisories will run through Monday as that is when the swell and surf look to peak before subsiding into mid week.

Long Term - Sunday Night Through Friday
500 MB pattern goes from not quite zonal weakly amplified flow, to Omega block by Monday, with trough situated over the CWA (County Warning Area) to becoming less amplified again by the end of the week. So, initially we deal with deepening closed low to our W Sunday into Monday, which will mean the best chance for precip, then the closed low sits over New England through the middle of the week, as it fills, and slowly shift NE by Friday. After the initial round of showers Sunday-Monday, it’ll turn much less humid and cooler through the middle week, with maybe some some isolated afternoon showers as we sit beneath a cold pool(a region of relatively cold air) aloft, then possible a warm trend Friday into next weekend.

Expect showers to become more numerous and frequent Sunday night, especially after midnight. Light ESE flow and increasing Tds, should be favorable for fog in many spots as well. Otherwise, mins should mostly be in the low to mid 60s. By Monday morning, should see widespread showers and perhaps some periods of light rain. TSRA are possible as well, especially away from the coast, and some convection could produce torrential downpours. Given the onshore and rain cant see maxes varying too much across the CWA, but the warm tropical air mass should allow for max temps of 70-75 in most spots. Coolest along the mid coast. The showers and storms continue into Monday evening before, the cold front moves through and winds switch to the W, probably around or after midnight. Mins range from the upper 50s in the mtns to the low 60s in the S.

Tue-Thu will be somewhat similar as the cooler air in the trough moves overhead. There will be the possibility of a few showers Tuesday and Wednesday afternoon given the cooler air aloft and the closed low overhead, and this will lead to partly sunny conditions as well, but the more part it should be dry with highs in the upper 60s to around 70 in the mtns and in the mid to upper 70s in the S. Overnight lows range from the upper 40s to low 50s in the N, to the mid 50s in the S. Still dry and maybe a little warn by Friday.

Marine
Short Term
Long period Swell from Hurricane Ernesto that is forecast to pass well SE of the Gulf of Maine will arrive later today. Building swell will generate seas greater than 5 feet by tonight with a SCA (Small Craft Advisory) likely Sunday into Monday due to seas. Winds will remain steady onshore with gusts generally less than 20 kts.

Long Term
Seas continue to be the main issue into early next week. Seas will peak on Monday in long period swell from Ernesto. Seas away from the coast could push to around 9 ft, while near shore waves could reach to around 6 ft. The seas will begin to slowly subside late Monday night and Tuesday.

NOAA Gray/Portland ME Office - Watches - Warnings - Advisories
ME...High Surf Advisory from 5pm Sunday to 8pm EDT Monday for MEZ023. High Surf Advisory from 2am Sunday to 8pm EDT Monday for MEZ024>028. NH...High Surf Advisory from 5pm Sunday to 8pm EDT Monday for NHZ014.

Marine
Small Craft Advisory from 8pm this evening to 8pm EDT Monday for ANZ150>152. Small Craft Advisory from 2pm Sunday to 8pm EDT Monday for ANZ153-154.