National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, ME

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-- Discussion containing changed information from previous version are highlighted. --978FXUS61 KGYX 171030AFDGYXArea Forecast DiscussionNational Weather Service Gray ME630 AM EDT Sat Aug 17 2024.SYNOPSIS...High pressure near the Gulf of Maine will maintainonshore flow and mostly dry conditions through the weekend. Afrontal system approaches late Sunday and crosses the area Mondayinto Tuesday bringing the next chance for widespread rainfall.Meanwhile, Hurricane Ernesto will be tracking north through thewestern Atlantic and staying well out to sea. Long period swell fromErnesto will start to arrive tonight and peak around Mondaybringing high surf and a rip current risk. High pressure thenbuilds in around the middle of next week.&&.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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630 AM Update...Only minor edits were made to reflectobservational trends.Previously...The persistent upper low in the Canadian Maritimes will lift outinto the Atlantic today with a mid level ridge axis sliding acrossthe forecast area. At the surface, an area of high pressure iscentered over southern Nova Scotia and will slowly drift eastthrough the day. Moist onshore flow beneath an inversion has ledto widespread low clouds and areas of fog to develop early thismorning. While deep layer ridging will keep the forecast areamostly dry today, mesoscale models suggest low clouds will bestubborn to scatter out this morning. As low clouds do scatterout late this morning some mid to high level clouds associatedwith a trough to the west of New England will start to spillinto the area. Additionally, there will still be some wildfiresmoke aloft over the area, but this smoke will eventually pulleast of the area as the upper low moves into the Atlantic. Thiswill lead to some filtered sunshine this afternoon after amostly cloudy start to the day.Long period swell from well offshore Hurricane Ernesto will start toenter the Gulf of Maine later today, although the greatest swellwill not arrive until late Sunday and Monday. Nevertheless, therewill be an increasing rip current risk late today as the swell firstapproaches the Mid Coast. Highs today will generally be in the mid70s along the coastal plain. Highs increase farther inland to theupper 70s across the north and low 80s along the CT Valley away fromthe marine influence.
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A trough over the Great Lakes will slowly slide east tonight withhigh pressure offshore providing moist onshore flow again tonight.This will bring low clouds and potential for fog along the coastalplain with chances for showers increasing west to east towards daybreak Sunday. Lows tonight will generally be in the upper 50s to low60s.The 00Z model suite suggests the trough over the Great Lakes makeslittle progress eastward Sunday as Ernesto tracks north through thewestern Atlantic. This will keep the best forcing for ascent to thewest of the area and have generally kept slight chance to low chancePoPs (15 to 30 percent) in the forecast. High pressure offshore willmaintain onshore flow with highs slightly cooler than today. Longperiod swell from Ernesto will still be on the increase approaching5 feet at 15 seconds towards the Mid Coast first then spreading towardssouthern beaches late Sunday. Have gone with a High Surf Advisoryfirst starting along the Mid Coast to coastal Cumberland Countystarting early Sunday morning with the High Surf Advisory not goinginto affect for areas south of Cape Elizabeth until late Sunday.High Surf Advisories will run through Monday as that is whenthe swell and surf look to peak before subsiding into mid week.
-- End Changed Discussion --&&.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 tobecoming less amplified again by the end of the week. So,initially we deal with deepening closed low to our W Sunday intoMonday, which will mean the best chance for precip, then theclosed low sits over New England through the middle of the week,as it fills, and slowly shift NE by Friday. After the initialround of showers Sunday-Monday, itll turn much less humid andcooler through the middle week, with maybe some some isolatedafternoon showers as we sit beneath a cold pool aloft, thenpossible a warm trend Friday into next weekend.Expect showers to become more numerous and frequent Sundaynight, especially after midnight. Light ESE flow and increasingTds, should be favorable for fog in many spots as well.Otherwise, mins should mostly be in the low to mid 60s. ByMonday morning, should see widespread showers and perhaps someperiods of light rain. TSRA are possible as well, especiallyaway from the coast, and some convection could producetorrential downpours. Given the onshore and rain cant see maxesvarying too much across the CWA, but the warm tropical air massshould allow for max temps of 70-75 in most spots. Coolest alongthe mid coast. The showers and storms continue into Mon eveningbefore, the cold front moves through and winds switch to the W,probably around or after midnight. Mins range from the upper50s in the mtns to the low 60s in the S.Tue-Thu will be somewhat similar as the cooler air in the troughmoves overhead. There will be the possibility of a few showersTue and Wed afternoon given the cooler air aloft and the closedlow overhead, and this will lead to partly sunny conditions aswell, but the more part it should be dry with highs in the upper60s to around 70 in the mtns and in the mid to upper 70s in theS. 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 byFriday.&&.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...Short Term...Onshore flow beneath an area of subsidence willcontinue a tricky aviation forecast through this morning as lowcigs and fog periodically impact some TAF sites. On the whole, thecombination of low cigs and fog will continue mostly IFRconditions through this morning with both periods of MVFR andLIFR depending on the behavior of cigs. Cigs look to lift laterthis morning for improving conditions into the afternoon.Onshore flow continues tonight for another round of likelyIFR/LIFR conditions while similar to last night there could besome sites that see periods of MVFR/VFR. Conditions likelyimprove during the day Sunday.Long Term...It looks like all terminals drop to IFR or lower infog and low cigs Sunday night, with only minor improvementduring the day on Monday with showers as well. IFR or lowerexpected Monday night before a return to VFR by midday Tuesday.&&.MARINE...Short Term...Long period Swell from Hurricane Ernesto that isforecast to pass well SE of the Gulf of Maine will arrive latertoday. Building swell will generate seas greater than 5 feet bytonight with a SCA likely Sunday into Monday due to seas. Windswill remain steady onshore with gusts generally less than 20kts.Long Term...Seas continue to be the main issue into early nextweek. Seas will peak on Monday in long period swell fromErnesto. Seas away from the coast could push to around 9 ft,while near shore waves could reach to around 6 ft. The seas willbegin to slowly subside late Monday night and Tuesday.&&.GYX WATCHES/WARNINGS/ADVISORIES...ME...High Surf Advisory from 5 PM Sunday to 8 PM EDT Monday for MEZ023. High Surf Advisory from 2 AM Sunday to 8 PM EDT Monday for MEZ024>028.NH...High Surf Advisory from 5 PM Sunday to 8 PM EDT Monday for NHZ014.MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT Monday for ANZ150>152. Small Craft Advisory from 2 PM Sunday to 8 PM EDT Monday for ANZ153-154.&&$$NEAR TERM...SchroeterSHORT TERM...SchroeterLONG TERM...Cempa