Penobscot Bay Marine Forecast
|Rest Of Tonight...S Winds 5 To 10 Kt, Becoming E Late. Seas Around 2 Ft. A Chance Of Showers Late This Evening, Then Showers. Patchy Fog. Vsby Variable To Less Than One Quarter Nm.|
|Thu...E Winds 5 To 15 Kt, Becoming Se 10 To 15 Kt In The Afternoon. Seas 2 To 3 Ft. Patchy Fog In The Morning. Showers. Vsby Variable To Less Than One Quarter Nm.|
|Thu Night...S Winds 10 To 15 Kt, Diminishing To 5 To 10 Kt After Midnight. Seas 2 To 4 Ft. Showers Likely, Mainly In The Evening With Vsby 1 To 3 Nm.|
|Fri...Sw Winds 5 To 10 Kt. Seas 2 To 4 Ft. A Chance Of Showers In The Morning.|
|Fri Night...Sw Winds 5 To 10 Kt. Seas 2 To 4 Ft. Patchy Fog After Midnight. Vsby Variable To Less Than One Quarter Nm After Midnight.|
|Sat...Sw Winds 5 To 10 Kt. Seas 2 To 3 Ft.|
|Sat Night...Sw Winds 5 To 10 Kt. Seas 2 To 3 Ft.|
|Sun...Sw Winds Around 5 Kt. Seas Around 2 Ft. A Chance Of Showers.|
|Sun Night...Se Winds Around 5 Kt, Becoming E After Midnight. Seas 1 To 2 Ft. A Chance Of Showers.|
|Mon...E Winds Around 5 Kt, Becoming S In The Afternoon. Seas 1 To 2 Ft.|
|Mon Night...S Winds Around 5 Kt. Seas Around 2 Ft.|
| Area Forecast Discussion|
National Weather Service Gray ME
949pm EDT Wednesday August 4 2021
Low pressure will track through southern New England later tonight, before passing through the Gulf of Maine Thursday morning possibly bringing some heavy rain to the coast. An upper level trough will bring more clouds to the region Friday, with high pressure building in at the surface through Saturday. Scattered showers and thunderstorms are possible Saturday night into Sunday as a frontal boundary crosses the region. Ridging will continue to build early to mid next week, with a warmer pattern becoming more established.
Near Term - Until 6am Thursday Morning
945pm Radar and ASOS reports indicate that some light rain shower activity has now reached portions of southern NH but the main precipitation shield is still off to the east over the waters. The latest few runs of the HRRR (High-Resolution Rapid Refresh) have trended downward in total Quantitative Precipitation Forecast as a result of keeping the steadiest and heaviest rainfall both to our south and east with little to no measurable rain reaching ME until around 09Z. As a result, Probability of Precipitation and Quantitative Precipitation Forecast were adjusted to account for these trends in both radar imagery and model guidance. Other than some minor tweaks to temperatures, dew points, and sky cover the rest of the forecast remains on track.
Previously... 530 PM...Some adjustments, mainly to timing of arrival of rain, more chance probability of precipitation later this evening in SE NH and coastal, and pushing the heavy potential until after midnight, and more likely, the heaviest will be around and after daybreak. Also adjusted temps a bit, although overall mins a re close to previous forecast, but most of the cooling happens this evening, especially in the S, with temps closer to holding steady later tonight. The HRRR (High-Resolution Rapid Refresh) continue to focus the heaviest along or just inland of coastal front, which would keep the heaviest of rain in SE NH and the ME coastal plain.
Previously...Satellite imagery this afternoon continued to show plumes of moisture developing off the Mid Atlantic coastline with convection firing along and ahead of a surface area of low pressure which was gradually forming just off the coastline. Radar imagery depicts rainfall off the New England coast, similar to most operational and mesoscale models near term forecasts.
Most operational and ensemble model solutions continue to have a significant model to model and run to run discontinuity. This is particularly true with the timing and evolution in the precipitation forecast. There has been an eastward shift in the high precipitation and Probability of Precipitation forecasts for tonight, with a couple mesoscale models bucking the trend and keeping heavy rainfall totals along the coast. This disparity remains relatively significant. Out of all the model solutions however, the Euro ensemble mean perhaps would lead to the most consistent forecast.
In any case, the forecast remains highly uncertain as any waiver in the track of the surface low and high PWAT (Precipitable Water) axis could shift the focus for heavy rainfall back to the coast and some inland areas. This system appears to be similar to the August 13, 2013 event, however this event is displaced further to the east.
After coordination with adjacent offices, will hold off on Flash Flood Watches for now as confidence is not sufficiently high to warrant these headlines. However, short term trends will need to be closely monitored during the overnight hours. Precipitation should advance north during the late evening hours.
Patchy fog is possible during the overnight hours as easterly winds begin to bring enhanced moisture off the Gulf of Maine. The cloud cover will make for relatively uniform temperatures from north to south with mid to upper 50s for overnight lows in most areas.
Short Term - 6am Thursday Morning Through Thursday Night
12Z models and ensemble solutions suggest a second period of shower activity on Thursday with showers continuing during the morning hours as the upper level low and jet streak crosses the region. Locally heavy rainfall may continue along and near the coastline with the highest totals potentially in the Midcoast region of Maine.
Surface dew points will continue to rise across the region as tropical air will remain nearby over the Gulf of Maine. The clouds and shower activity will limit daytime highs to the lower 70s in most areas.
The chance for showers will continue to diminish Thursday night as the upper level trough pushes east. Nighttime lows will drop into the mid 50s to lower 60s.
Long Term - Friday Through Wednesday
General pattern in the extended will consist of a sprawling Bermuda High along the Eastern Seaboard through Saturday night before a progressive polar jet becomes reestablished bringing mid-level shortwaves between periods of ridging next week. Overall pattern will support above average temperatures and near normal precipitation with rain chances on Sunday and Tuesday night.
All rain ends by daybreak on Friday with zonal flow aloft and ridging at the surface as the Bermuda high becomes dominate along the eastern seaboard. SW return flow will become established with a hot and humid airmass in place as dewpoints surge into the upper 60s with heat index values reaching the mid to upper 80s. Still muggy on Saturday and mostly dry on the coastal plain with chance for afternoon showers and thunderstorms across the interior mountains. Weak surface cold front pushes through on Saturday night into Sunday morning along with a 500mb shortwave trough. This will bring in a slightly cooler airmass, but by no means a big cool down. Shower activity will be more widespread across interior areas. Warm and humid airmass returns for the beginning of next week with the potential for instability showers/thunderstorms. No significant widespread events on the horizon at this time.
Easterly winds will pick up tonight into Thursday with a few gusts to 20 kt, just below Small Craft Advisory criteria. Winds will switch to the north Thursday night. Seas will gradually be on the increase with a few waves near 5 feet along the outer waters Thursday night.
High pressure is expected over the coastal waters through this period with predominate flow out of the southwest. Seas and winds will stay below SCA (Small Craft Advisory) conditions but gusts up to 20kts could be possible this weekend. Pattern will also support the chance for fog and low visibilities at times.
Much uncertainty continues from model to model and run to run in terms of the Quantitative Precipitation Forecast in the short term portion of the forecast. There is a consensus that the highest rainfall totals will fall along the coast where an inch or two of rain may fall in about a 12 hour period which remains above flash flood guidance values. These amounts will likely need to be adjusted and modified however as radar and satellite signatures are identified during the overnight hours. Therefore, conditions will still need to be monitored for the possibility of a Flash Flood Watch.
NOAA Gray/Portland ME Office - Watches - Warnings - Advisories
ME...None. NH...None. MARINE...None.