Marine Weather and Tide Forecast for South Portland, ME

KEY MESSAGES
1. Near to slightly below normal temperatures expected for Friday and Saturday with intermittent chances for showers.

2. Seasonable temperatures warm late this weekend into early next week. Rain chances remain concentrated on Sunday and towards the middle of next week.

DISCUSSION
KEY MESSAGE 1 DESCRIPTION...
Dreary conditions continue the rest of today with a cold front lurking just to our west. Ahead of this front, the HRRR is pretty consistent in showing the current batch of rain continuing to advance to the northeast, generally expected to move out of the area by sunset. There may then be period of drizzle, but overnight looks mostly dry with just a few showers possible.
Between now and 00Z/8PM this evening, this activity may result in additional rainfall amounts of 0.25" to 0.50" across western ME with the higher amounts toward the Kennebec Valley and Midcoast. Outside of precipitation, patchy fog is possible, but chances of this should come to an end as the boundary level becomes a bit drier and better mixed later this evening and tonight behind the front. Not sure how mixed we'll end up being, but W-NW winds may get a bit breezy with gusts to around 20-25mph, per RAP and HRRR forecast soundings.

Drier conditions are expected Friday, but a slow-moving 500mb low will still reside north of the Great Lakes and will continue to send waves of energy and broad lift through the area. While the atmosphere is only marginally conducive for a few showers in the afternoon, but there should still be enough moisture and MUCAPE for a diurnal cu field. Highs will be mostly in the upper 50s to lower 60s, which is near to slightly below normal. Northwest winds could be breezy at times with gusts of 20-25 mph, possibly up to 30 mph in the morning. This should be enough to hold off or to delay the seabreeze to bring these warm temperatures to the coast.

Today's 12Z HRRR and 3km NAM are showing an area of showers approaching from the west around sunset and then gradually moving into NH and western ME later in the evening overnight. The latest NBM is starting to latch onto this, and the 20-30% will do for now, but these might have be nudged upward if the trends in the CAMs hold. Currently lows are forecast to be in the 30s, which may result in patchy frost, but more clouds with the showers holding together would keep temperatures a little warmer.

The same upper low will not have moved much from Friday into Saturday, but as waves aloft pass by, shower development looks more favorable as overall moisture and instability looks higher than that of Friday. This should also result in more clouds and hold temps a couple of degrees cooler than Friday. The gradient will also be weaker to allow the seabreeze at the coast.

KEY MESSAGE 2 DESCRIPTION...
Low pressure will be exiting the Carolina coast Saturday night, moving north-northeast offshore. While the current track keeps the center of the low well to the east, its moisture field broadens and will come in proximity to the coast and coastal waters. NBM trend has been to bring measurable precip into the coast and interior Sunday. For lows that are more compact and travel a bit further off the coast, dry air typically funnels in on the western periphery due to NW continental air mass, creating a sharp edge to precipitation. This is still a possibility, but guidance moisture profiles are humid. This encourages leaving showers in the forecast at this time. Did narrow the spread of measurable precip to the coast and portions of the interior.

As a result, Sunday will feature mainly overcast skies with increasing north to northwest winds through the afternoon. High temperatures may be the coolest for the following few days, as highs climb into the mid 50s before pushing into the 60s and even lower 70s early next week.

The second chance for widespread rain comes midweek as low pressure occludes south of Hudson Bay. As the main low lags, cut off from an intensifying lower jet from Texas to the Northeast, triple point low pressure may develop in vicinity of the St Lawrence River and continue NE. This could introduce a brief warm sector to northern New England, but more importantly it signals moisture transport could become more parallel to frontal forcing along the approaching cold front. The slowing front then becomes a focal point for this water vapor transport to fall out as precipitation. Timing and location of of the front varies widely at this time, but would look towards the middle to second half of the week for impacts on the forecast area.

AVIATION /00Z FRIDAY THROUGH TUESDAY/
Through Friday...IFR and lower conditions continue to slowly improve to MVFR across the area. In general I opted for a blend of guidance to balance the faster clearing of the HRRR and the slower clearing of the statistical models. The overall theme will be improvement though, with VFR conditions returning to terminals by morning. I cannot rule out a stray shower overnight, but generally dry conditions expected. Fri afternoon may see winds get briefly gusty, with west northwest surface gusts of 20 to 25 kt possible.

Outlook...

Friday night: MVFR ceilings possible along with a chance of showers.

Saturday: MVFR cigs possible in the morning. A few showers possible during the day along with a seabreeze/wind shift for coastal terminals.

Saturday Night: Clouds thicken and lower with MVFR possible. IFR bases possible near the coast along with some fog. SHRA for coastal terminals, uncertain if these make it towards AUG/CON.

Sunday: MVFR ceilings continue through the morning with SHRA.
Gradual improvement towards VFR SW to NE into the early evening hours.

Sunday Night: Mainly VFR, valley fog possible.

Monday and Tuesday: Some restrictions possible as SHRA again push into the region. These are most likely for terminals in the western half of the forecast area.

MARINE
Through Saturday...SCA conditions continue over the coastal waters through Friday evening, mainly due to seas staying elevated. A cold front crosses the waters this evening and tonight with winds shifting to west to northwest. High pressure becomes centered south of the waters Friday into Saturday with seas subsiding through Saturday.

Winds become northeast Saturday night as low pressure passes just outside the Gulf of Maine through Sunday. Winds and waves will remain below SCA criteria through much of Monday, until low level winds increase from the SW Monday night through Tuesday.
This could bring a period of Gales and increasing wave heights to the waters Tuesday through the middle of next week.

GYX WATCHES/WARNINGS/ADVISORIES
ME...None.
NH...None.
MARINE...Small Craft Advisory until 8 PM EDT Friday for ANZ150-152>154.
Small Craft Advisory until 8 PM EDT this evening for ANZ151.