Marine Weather and Tide Forecast for South Portland, ME

NEAR TERM /UNTIL 6 AM FRIDAY MORNING/
1105 PM Update...There will continue to be chances for showers and occasional thunder across northern zones for the next couple of hours while the threat for severe storms has ended. Repeat rounds of thunderstorms did prompt a Flood Advisory across central Franklin and central Somerset Counties that remains in effect until 1230 AM EDT as showers upstream are tracking towards this area. Have mainly refined PoPs with this update in addition to ending the enhanced wording with thunderstorms.

840 PM...Have canceled the Severe Thunderstorm Watch for much of the area with the exception of northern Counties where current sub-severe storms show some signs of brief intensification. Expect the severe threat to gradually diminish with the loss of heating while repeat rounds of convection across central Somerset County are introducing a flood threat.
Will continue to monitor this area for potential short fused flood products over the next hour.

632 PM Update...Going forecast is largely in good shape with the main focus of this update to refine PoPs and thunderstorm coverage through this evening. A slight capping inversion noted on the 19Z KGYX sounding and the best forcing still back over Upstate NY has helped to keep storms widely scattered across the interior. The best ML CAPE and shear is located along a corridor from the Lakes Region of NH through the western mountains of Maine to the Canadian Border where there are currently three Severe Warnings out. Satellite trends suggest a stable marine layer has pushed into the coast and recent runs of the HRRR suggest chances for storms here and even across southern NH will be very low. No changes to the current Severe Watch as enough instability and shear will remain in place over the next couple of hours that could sustain any additional storms that develop mainly north of the Lakes Region of NH and the foothills of western Maine.

Previously...

Clouds have largely cleared out since this morning (with the exception of the Midcoast), and this has set the stage for sufficient instability this afternoon thanks to the resultant warming and dewpoints in the mid 60s to low 70s across much of the area. Lift is also increasing across the area as a cold front continues to approach from the west, and 30-40 kt of 0-6km shear combined with the unstable conditions has created an environment for some storms to become strong to severe this afternoon and evening. Convection is already starting to develop, and coverage/intensity should steadily increase the rest of this afternoon and evening. The greatest threat is along and to the north and west of the I-95 corridor, and a Severe Thunderstorm Watch has been issued until 11 PM for much of western ME, mainly for damaging winds and large hail in excess of 1" in diameter. There is also a veering wind profile and enough 0-1km SRH to where the could be a brief tornado or two. The risk is lower along the coast where the seabreeze has moved in. Torrential downpours will accompany thunderstorms, and even though storms will be moving quickly, there is a conditional threat of isolated flash flooding if any location receives multiple storms.

Instability may be sufficient enough for the threat of strong to severe storms to last an hour or two beyond sunset, but coverage and intensity will steadily wane after 10 PM with remaining storms expected to become more elevated in nature. Storms should then be mostly done by midnight or so, but some showers stick around through tonight, mostly in the mountains. South of the mountains, expecting a gradual decrease in cloud cover overnight, although cloudier skies may stay put across eastern areas along with some fog. For the rest of the area, can't rule out patchy fog, but I think winds will be up enough to where it shouldn't be too much of an issue. Winds may start becoming breezy toward daybreak across western areas behind the cold front.

SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/
Low pressure will be centered just to the north of the area to start out Friday with the cold front nearing the Midcoast. he front will quickly exit to the east as the low moves across the St. Lawrence Valley, and the increased westerly winds behind the front will clear out any lingering stratus/fog around the Midcoast by mid-morning.

And speaking of winds, that will be the main story for Friday. Model soundings continue to advertise wind gusts of 30 to 40 mph in the morning and afternoon, and the top of the mixed layer supports the potential for some to top out in the 45 to 50 mph range, which could result in damage to tree branches and even power outages. Given the threat of severe weather today, have opted to hold off on any additional headlines, but a Wind Advisory for Friday could be issues as early as later this evening once the threat of severe weather winds down.

Drier air behind the front will keep locations south of the mountains mostly dry, although there will still be enough moisture for partly sunny skies with maybe a few periods of mostly cloudy. In the mountains, more cloud cover is expected with a chance of showers thanks to upslope flow. High will be mostly in the mid 70s to low 80s, except a tad cooler in the mountains.

Winds will ease Friday evening with the loss of mixing and will continue to do so through the overnight hours. The last of the upslope showers should also come to an end in the evening. Lows will be mostly in the 50s with a few low 60s mixed in.

LONG TERM /SATURDAY THROUGH THURSDAY/
1105 PM Update...No significant changes in the latest NBM with strong signal for dangerous levels of heat and humidity Monday into Tuesday. It does look like this will be a short duration heat event with temperatures abating Wednesday into Thursday.


Dangerous Heat Monday Through Tuesday

By Saturday the region will remain under the influence of upper- level NW flow aloft, as ridging begins to take shape to our south.
The lower dewpoints will rebound slightly, but generally allowing for low humidity with temps 75-85 from N to S under ample sunshine.
As the ridge builds to our south Saturday Night, attention will turn to upstream convection that models have shown traversing on the periphery of the ridge into New England by Saturday Night. There is low confidence on the placement of this feature, but have upped pops due to the run to run consistency. The residual cloud cover will linger through at least midday Sunday as a warm-front lifts north.
Humidity values will surge with dewpoints in the upper 60s.

Attention then turns to the much advertised heat dome with 500mb up to 600 dm across the eastern U.S. by Monday through Tuesday.
Temperatures will reach 90 for many areas from the foothills southward, warming another 5 degrees or so further by Tuesday.
Forecast temperatures are at/near record highs for some locations, particularly for Tuesday which looks to be the hottest day of the forecast. The humidity will be elevated as well, leading to heat index values into the mid 90s and towards 100 degrees in a few locations. The heat will linger until a cold front from Canada drifts south. There is low confidence in the timing of this feature, with a few model guidance suggesting heat could linger into Wednesday, at least for S NH. The front will bring some showers and thunderstorms, which is currently forecast for Tuesday night. How far south the boundary sags south will greatly impact how much relief from the heat the region will experience.

AVIATION /03Z FRIDAY THROUGH TUESDAY/
Short Term...Expecting generally VFR outside of showers and storms into early this evening with the exception of low ceilings or even fog in the PWM-AUG-RKD corridor. Showers and storms expected to move into the region around 21Z this afternoon and could provide TEMPO IFR conditions through around 02Z/20 this evening and may also include strong wind gusts and hail. Storms will then mostly end by 03-04Z with lingering showers possible overnight, mostly in the mountains.
A cold front will approach overnight and begin crossing through around daybreak Friday, and until it crosses, it's possible to see more fog or low stratus, again more likely in the PWM-AUG-RKD region.

HIE and possibly LEB will see a chance of showers through at least the first part of Friday and may also hold onto MVFR ceilings. The rest of the terminals are expected to to remain VFR on Friday, but the main story will be the gusty W/WNW winds. It looks like most gusts will fall into the 25 to 35 kt range, but it's possible some could top out 40-45 kt. Winds will then follow a downward trend Friday evening through Friday night while VFR is expected to continue.

Long Term...Mainly VFR Saturday with increasing chances for showers and storms Saturday night into early Sunday with restrictions possible. VFR then expected Monday and Tuesday.

MARINE
Short Term...A cold front approaches continues to approach the waters, and then eventually starts to cross through around daybreak and through Friday morning. Increasing southerly winds will bring SCA conditions starting this evening, and these will continue through Friday behind the cold front as winds turn west to southwesterly.
Winds stay westerly Friday evening/night and will diminish, allow conditions to fall below SCA levels.

Long Term...An extended period of great boating conditions are expected this weekend through early next week with a ridge over the region. Winds will be variable to SE/SW at times between 5-15 kts. Seas will be 1- 3 ft for much of the period.

GYX WATCHES/WARNINGS/ADVISORIES
ME...None.
NH...None.
MARINE...Small Craft Advisory until midnight EDT Friday night for ANZ150.
Small Craft Advisory from 4 AM to 8 PM EDT Friday for ANZ151- 153.
Small Craft Advisory until 8 PM EDT Friday for ANZ152-154.