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Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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563 FXUS61 KGYX 202312 AFDGYX Area Forecast Discussion National Weather Service Gray ME 712 PM EDT Fri Sep 20 2024 .SYNOPSIS... Low pressure south of Cape Cod meanders through tomorrow before slowly drifting southward by early next week. The low continues to bring cooler conditions, a few showers, and impacts along the coastline. High pressure builds in across New England by late this weekend and early next week, bringing seasonable temperatures and dry conditions. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 710 PM Update... Went ahead and allowed the high surf advisory to expire on time as the sun sets across the region. Radar imagery continues to show mainly weak returns across the Gulf of Maine and approaching the coastline with a few reports of sprinkles thus far. Fine tuned PoPs through the overnight hours based on latest radar trends and hi-res guidance, which keeps the majority of mentionable PoPs along the immediate coast. Otherwise, just made some minor adjustments to temperatures, dew points, and winds. Previously... A large band of precipitation over the Gulf of Maine will continue to attempt to retrograde westward as the moisture interacts with dry air over land. This attempt at the pivoting of precipitation remains in association with a nearly stationary surface low southeast of Cape Cod along with an upper level low stacked over the system. Most available guidance keeps much of the region dry, but also brings some measurable rainfall to the southwest coast of Maine and the Seacoast of New Hampshire. The latest Namnest solution brings over a quarter inch of precipitation to this region showing somewhat of a Norlun looking inverted trough overnight. Will monitor the development of this boundary this evening, however, considering how dry it has been and dry level in place across the interior, this precipitation may be overforecast and in more agreement with other model solutions which keep limited precipitation over the region. Along portions of the southwest coast of Maine and the Seacoast of New Hampshire, dangerous surf will continue with rip currents. Elsewhere, mainly dry conditions can be expected outside an isolated shower. Patchy drizzle can be expected over southeast New Hampshire and southern Maine with patchy fog as well once again tonight. Temperatures will be slightly cooler tonight, mainly in the upper 40s and 50s. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Any precipitation will be limited to far southern areas once again on Saturday. Low pressure will remain southeast of Nantucket before beginning its exit out to sea Saturday night. Drier air will then enter all areas at that time setting the stage with a sunny end to the weekend for all areas. Highest temperatures will be over northern areas on Saturday where the most sunshine will occur, mainly in the 60s. A backdoor high pressure system will enter the region from the Canadian Maritimes Saturday night. This will allow for temperatures to be a little cooler, mainly in the 40s to lower 50s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Overview: Uncertain weather pattern evolving in the extended after the breakdown of a block. After upper low lifts out of the Gulf of ME...the blocky nature of the pattern will remain. Guidance attempts to set up another rex block but the location remains low confidence. Impacts: Pretty wide range of potential impacts...from continued dry weather and increasing fire weather risk...to a more changeable pattern with rain chances. Forecast Details: The higher confidence portion of the forecast this weekend will feature at least brief ridging as upper low departs the local waters and drifts east. Northeast flow should keep temps on the near normal side versus the mild weather of late. We will also have to keep an eye on lingering moisture and potential fog/stratus near the coast before westerly winds can sweep it away. Beyond Mon a trof will approach from the west and that is where forecasts diverge. Some guidance favors the base of the trof cutting off and pinwheeling around for several days. Other guidance favors a more progressive trof. Some of this may be tied to potential tropical cyclone development in the Gulf of Mexico later in the period...and ridge building ahead of it. Examining clusters in DESI...guidance is roughly split 50/50 between the two ideas...though the location of the cutoff will determine local sensible weather. As a result I will not stray too far from the multi-model consensus blend. In general temps will gradually moderate thru the week. Rain shower chances will develop by midweek and may linger into the weekend. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/... Short Term...HIE and LEB may see nighttime valley fog again tonight. A few showers are possible along the coast and southern New Hampshire through at least tomorrow morning, and then ceilings gradually improve to VFR by late in the day Saturday into Saturday night. Long Term...Generally VFR conditions expected to start the period...though there is a low probability of some IFR or lower conditions near the coast in marine fog/stratus. Local MVFR or lower conditions possibly develop by midweek in SHRA as a trof approaches from the west. Valley fog would be most likely Sun night/Mon morning as surface ridge noses into the region from the northeast. && .MARINE... Short Term...SCA conditions continue over the outer waters through tomorrow night as a gale center lingers south of Cape Cod. A few gale force gusts can be expected near IOSN3. The system gradually begins to drift southward by late Saturday, but seas remain elevated even as winds begin to gradually decrease. Long Term...Behind the departing low pressure northeast winds may gust near 25 kt outside of the bays on Sun. That will support continued wave heights above 5 ft. Those will gradually diminish thru the week...but may remain at or above 5 ft thru at least Thu. && .TIDES/COASTAL FLOODING... We are at the peak of our astronomical tide cycle through the weekend with the highest tides occuring during the afternoon hours. Meanwhile, a gale center will remain south of Cape Cod over the next few days. This will lead to multiple cycles of minor coastal flooding due to storm surge values around a foot, mainly from Portland and points south. Beach surveys and Emergency Managers continue to indicate compromised dune systems along the coastline from our storms this past winter. Therefore, building nearshore waves may lead to splash-over as well. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Coastal Flood Advisory from 1 AM to 4 AM EDT Saturday for MEZ023-024. High Surf Advisory from 8 AM to 7 PM EDT Saturday for MEZ023- 024. NH...Coastal Flood Advisory from 1 AM to 4 AM EDT Saturday for NHZ014. High Surf Advisory from 8 AM to 7 PM EDT Saturday for NHZ014. MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ150>154. && $$ NEAR TERM...Tubbs SHORT TERM...Cannon LONG TERM...Legro