Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 050438 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1238 AM EDT Wed Aug 5 2020 .SYNOPSIS... Showers and thunderstorms associated with TS Isaias will become more numerous through this evening, especially across NH. Winds will pick up later this afternoon as well then the brunt of the storm with locally heavy rainfall should hit this evening into the pre- dawn hours Wednesday. The storm exits to the north early Wednesday with temperatures settling near normal and lower humidity levels for Thursday and Friday. Temperatures and humidity will begin to creep up over the weekend, but it will remain mainly sunny and fair. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1230am Update...Just a quick AFD-only update here to note that we have cancelled all of the inland TS warnings and also the flash flood watch. TS warnings remain up along the coast at least until the next NHC advisory update. Update...Made a fairly comprehensive update in preparation for the 03z NHC update for Isaias. Biggest changes were to speed up timing of both PoP and winds thru the forecast area as the storm accelerates. Winds are consistently gusting between 30 and 40 knots and should generally remain there for the next hour or two. Winds are steadily decreasing to our SW...and that will be the trend locally as well. The majority of the heavy rain has also moved out of the forecast area...and so I will be evaluating taking the flash flood watch down with the next advisory package as well. Slow but steady improvement is on the way. Previous discussion...At 19z a 994 millibar tropical low was vicinity of the Tri-State Region...with three hour pressure falls on the order of 10 millibars across that area. Latest surface analysis remains in good agreement with current track forecast as the center of Isaias races northward into the Hudson Valley. Shear continues to increase across our area as we are in the favored quadrant for strong convection along with isolated tornadoes. Expect scattered low-topped rotating storms through early evening with brief spinups and damaging surface winds gusts with the stronger cells. Per latest HREF, a band of convection entering southern New England on NWS Doppler Radar mosaic will pivot northward across the area this evening, accompanied by strong wind gusts and brief heavy rain. Accompanying this band will be a plume of precipitable water approaching two inches. Strong upslope flow into our favored higher terrain could result in some localized flooding as this band crosses the higher terrain. Convection will quickly end from south to north overnight as the decaying tropical system accelerates into southeast Canada. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Behind this system...we could see a stray shower across northern areas Wednesday as a weak cold front crosses the area. Otherwise a partly to mostly sunny day with highs mainly in the 80s. Behind the cold front...mainly clear and less humid with some patchy valley fog possible. Lows will range from the mid 50s to lower 60s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... A quiet stretch of weather awaits the long range forecast period for the end of this work week into the start of the next. By Thursday morning, an upper level trough will be exiting east across the Canadian Maritimes...in its wake a mid-level thermal trough crosses into New England with h850 temps dipping a little below normal, to about 8-10C. A little low level moisture in westerly flow will lead to some clouds over the mountains but other than that weather will be fair with comfortably afternoon highs in the 70s to low-80s and dew points in the 50s. Broad surface high pressure builds into New England by Friday which ought to keep showers along a weak boundary south of the forecast area, although there will be an uptick in humidity over the southern part of the forecast area. An upper level shortwave approaches the coast late Friday which produces some cyclogenesis along the aforementioned boundary over the waters; while widespread rain isn`t expected it could fling enough moisture back into New England to produce widely scattered mountain rain showers during the afternoon as the trough axis aloft crosses. A ridge of high pressure crosses Sunday into Monday with more dry weather; meanwhile a southwest wind sets up over the eastern CONUS, trending temperatures up through the weekend and into the middle of next week. High temperatures are expected to warm well into the 80s and into the low-90s over the interior by Monday. A series of weak shortwaves bring PoPs back at least over the mountains during the first half of the coming wAVIATION... MARINE... HYDROLOGY... TIDES/COASTAL FLOODING...eek. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Short Term /through Wednesday Night/...TS Isaias will bring widespread MVFR/IFR conditions and gusty winds this evening, with conditions improving from south to north Wednesday morning to widespread VFR along with decreasing winds. Valley fog possible Thu AM vcnty of KHIE/KLEB. Long Term...VFR prevails through the end of the work week and weekend with high pressure over the area. Low clouds and fog may impact valley and coastal sites Friday and Saturday mornings... and possibly at HIE/LEB Sunday morning. && .MARINE... Short Term /Through Wednesday Night/...Strong south to southeast winds expected with the passage of TS Isaias tonight along with building seas. Winds will diminish overnight but seas above 5 ft are likely to linger for Wednesday. Long Term...A quiet period of weather is expected for the end of this week and into the next as weak high pressure settles over the region and gradually sAVIATION... MARINE... HYDROLOGY... TIDES/COASTAL FLOODING...lides east into the Atlantic. Seas start to build ahead of an approaching trough by the beginning to middle of the next work week. && .HYDROLOGY... Showers and thunderstorms associated with TS Isaias could produce torrential downpours this evening. Western areas can expect the highest rainfall totals, especially across the higher terrain in the mountains where southeasterly upsloping will occur. One to two inches with as much as three inches of rain is possible across the favored upslope terrain. Elsewhere...generally less than an inch is likely. Heavy rain could lead to localized flash flooding. && .TIDES/COASTAL FLOODING... A modestly high astronomical tide will occur shortly after midnight tonight. 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 tonight. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Tropical Storm Warning for MEZ023>028. Coastal Flood Advisory until 2 AM EDT early this morning for MEZ023>028. NH...Tropical Storm Warning for NHZ014. Coastal Flood Advisory until 2 AM EDT early this morning for NHZ014. MARINE...Tropical Storm Warning for ANZ150>154. && $$ NEAR TERM...Watson SHORT TERM...Cannon/Schwibs LONG TERM...Casey

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