Penobscot Bay Marine Forecast
|Tonight...W Winds 5 To 10 Kt. Seas 2 To 3 Ft.|
|Tue...S Winds Around 5 Kt. Seas 1 Foot Or Less. A Chance Of Showers Late.|
|Tue Night...Tropical Storm Conditions Possible. Se Winds 5 To 10 Kt With Gusts Up To 20 Kt, Becoming S 25 To 30 Kt With Gusts Up To 40 Kt After Midnight. Seas Around 4 Ft, Building To 6 Ft After Midnight. Showers Likely With A Chance Of Tstms In The Evening, Then Showers Likely After Midnight With Vsby 1 To 3 Nm.|
|Wed...S Winds 15 To 20 Kt, Becoming Sw 10 To 15 Kt In The Afternoon. Seas 3 To 4 Ft. A Chance Of Showers In The Morning. Vsby 1 To 3 Nm Until Late Afternoon.|
|Wed Night...W Winds 5 To 10 Kt. Gusts Up To 20 Kt In The Evening. Seas Around 3 Ft.|
|Thu...W Winds 5 To 10 Kt. Seas Around 2 Ft In The Morning, Then 1 Foot Or Less.|
|Thu Night...W Winds 5 To 10 Kt. Seas 1 Foot Or Less.|
|Fri...W Winds Around 5 Kt, Becoming Sw In The Afternoon. Seas 1 Foot Or Less.|
|Fri Night...W Winds Around 5 Kt. Seas 1 Foot Or Less.|
|Sat...Sw Winds 5 To 10 Kt. Seas 1 Foot Or Less. Winds And Seas Higher In And Near Tstms.|
Area Forecast Discussion|
National Weather Service Gray ME
308pm EDT Monday August 3 2020
By later tonight will start to see some showers associated with Isaias moving into the region, which will become more numerous during the day on Tuesday. The brunt of the storm should hit Tuesday night with strong winds and locally heavy rainfall. The storm exits to the north early Wednesday, with more normal to warm temperatures and lower humidity for the end of the week.
Near Term - Through Tonight
Moisture will begin to spread north tonight ahead of tropical cyclone Isaias into western New Hampshire as a deep southerly flow develops over the region. Lows will remain in the mid to upper 60s over southern areas as this moisture advances into the region at all levels.
Short Term - Tuesday Through Tuesday Night
Showers become more numerous during the day Tuesday as winds increase from the south. Precipitable water levels will become very high once again. This deep moisture advecting poleward will allow for heavy showers. Destabilization of the atmosphere will allow for a few thunderstorms as well.
As Isaias continues to track north, plenty of shear will be present. An isolated thunderstorm or two may lead to the possibility of a tornado Tuesday night as the system tracks into and through our area. In general, 12Z model guidance suggests the timing of this system will be faster than previous runs with most of the rainfall exiting into Canada by Wednesday morning. Slight westward adjustments continue for the track.
Gusty south to southeasterly winds will continue with the passage of the cyclone as it moves up the Connecticut River Valley Tuesday night. Strongest gusts will be over the south facing higher terrain and the shoreline.
Long Term - Wednesday Through Monday
First things first... Wednesday sees the expedited departure of Tropical Storm Isaias, or its remnants. By then, the system will be undergoing or will have undergone extratropical transition as a northern stream trough over the Great Lakes swings an axis across the northeast Wednesday with a drying, westerly breeze in its wake. Latest model guidance suggests the shield of stratiform rainfall associated with the system is more or less out of our forecast area and into northern Maine by 12Z/8AM Wednesday; there remains some uncertainty in the forward speed and general timing of the tropical system with significant acceleration expected as it travels up the coast, but latest model guidance is converging on the system center lofting into the lower St Lawrence Valley by 12Z. Some wrap around moisture may generate a few rain showers over the mountains during the day Wednesday before drying entirely by that night. Some of those showers may track into the lower elevations, but would be minor and there isn't confidence to include in the forecast for now. Temperatures will warm into the 70s and 80s as skies clear out with a west to southwest breeze at about 10 kts (after gustier winds from the stratiform shield exit to the north).
Beyond Wednesday, the long range forecast looks fairly quiet. High pressure builds at the surface over the northeast CONUS with persistent SW flow aloft as a trough hangs back over the Great Lakes region and ridging holds over the Atlantic. Thursday will be quite nice with highs in the 70s to mid-80s and lowered dew points in the 50s under mostly sunny skies. After that, a warm trend carries into the start of next week with steadily increasing dew points. Highs will once again approach 90 over interior/southern locations by the start of next week. A few shortwaves cross to the north this weekend into next week with afternoon showers over the mountains possible.
Strong south to southeasterly winds expected with the passage of Isaias Tuesday night. A tropical storm watch remains in effect. Seas will be building to around or just over 10 feet by the time of high tide Tuesday night.
Long Term...The remnants of Isaias will be lofting north into the St Lawrence Wednesday and well away from the Gulf of Maine, allowing seas to gradually subside. Seas will linger around 5 ft over the outer waters, especially toward the Maine MidCoast, into Wednesday evening before high pressure builds into the region. Quiet over the waters for the end of the week and weekend.
Showers and thunderstorms could produce torrential downpours Tuesday ahead of Isaias, but heaviest rainfall is likely late tuesday and Tuesday night. Western areas can expect the highest rainfall totals, especially across the higher terrain in the mountains where southeasterly upsloping may occur. Two to four inches of rain can be expected throughout the region with potentially locally higher amounts in the higher terrain. Flash flooding and river flooding will also be possible with this system, hence a flash flood watch has been issued.
Tides / Coastal Flooding
A modestly high astronomical tide will occur shortly after midnight Tuesday night. As the remains of Isaias pass by to our west, a strong south to southeasterly flow may coincide with this tide depending on the exact timing with the system. Building seas and gusty onshore winds may allow for about a foot or so of storm surge (current model runs appear to have a low bias). This may lead to localized splash-over across the region Tuesday night. Timing of the system will critical.
NOAA Gray/Portland ME Office - Watches - Warnings - Advisories
ME...Tropical Storm Watch for MEZ007>009-012>014-018>028-033. Flash Flood Watch from Tuesday afternoon through late Tuesday night for MEZ007>009-012-013. NH...Tropical Storm Watch for NHZ001>015. Flash Flood Watch from Tuesday afternoon through late Tuesday night for NHZ001>009-011-015. MARINE...Tropical Storm Watch for ANZ150>154.