468 FXUS61 KPHI 110143 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 943 PM EDT Wed Oct 10 2018 .SYNOPSIS... High pressure will remain centered offshore through tonight. A strong cold front will then arrive later Thursday, which will interact with the remnants of Hurricane Michael as it accelerates northeastward and off the Mid-Atlantic coast later Thursday night and Friday morning. High pressure then builds in later Saturday before shifting offshore during Sunday. The next cold front and an associated upper level trough should arrive next Monday followed by the return of high pressure Tuesday. Another frontal system may arrive by next Wednesday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Partly cloudy skies over the forecast area as of mid evening will become increasingly cloudy as we head into the overnight hours. The IR satellite loop shows plenty of moisture at mid to high levels streaming northward from Michael into the mid- Atlantic states. So far the precip remains well to our west, and so following hi- res model guidance, have delayed the increase in hourly PoPs to after midnight. With the increasing cloud cover and light southerly winds, temps overnight should not fall more than a couple of degrees from the current readings. Have kept a mention of patchy fog in the forecast, but again the cloud cover will probably limit fog formation. Previous discussion: Southerly flow behind Bermuda high pressure east of the Carolinas will continue to usher a warm and humid airmass into the region with surface dewpoints slowly rising through the upper 60s and into the low 70s tonight. Hurricane Michael has made landfall over the Florida Panhandle, and will weaken as it tracks to the northeast towards the SC/GA border late tonight. Meanwhile, a cold front over the western Great Lakes will slowly track to the east tonight, and should be through most of the Ohio Valley by daybreak Thursday. For the local area, this means another warm and humid night with overcast skies and fog. Some mid-level shortwave energy will race out ahead of that front, and tapping into tropical moisture associated with Hurricane Michael, will produce showers that will move into western zones after midnight tonight and through daybreak Thursday. With abundant low level moisture in place, as noted by model PWATs well over 2", some of those showers could produce heavy rainfall, as well as a rumble of thunder. A quarter to a third of an inch of rain is possible from around midnight tonight through daybreak, mainly north and west of I-95. Lows tonight will be in the upper 60s to low 70s. Quite reminiscent of the warm and humid August nights of this past summer. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/... Hurricane Michael will weaken by Thursday morning, and continues to track to the north and east, passing over the Carolinas as a Tropical Storm on Thursday, then south of Delmarva and into the western Atlantic ocean waters Thursday night. Michael then moves out to sea on Friday. A cold front moving through the Ohio Valley will be west of the region by Thursday evening. Even though the storm will remain well to the south, frontogenetic banding out ahead of the cold front and on the backside of the departing Tropical Storm Michael will set up somewhere along the I-95 corridor Thursday afternoon and evening. There is some concern as to exactly where it will set up, whether it is along I-95, or 20 miles to the east or west, but there is at least enough confidence to suggest a period of heavy rainfall Thursday afternoon and night along the I-95 corridor, into the Coastal Plain of NJ, as well as Delmarva. A Flash Flood Watch is now in effect for those areas, as a widespread 2-3 inches of rain, with locally higher amounts, Thursday afternoon and Thursday night. Southerly flow continues to usher a tropical airmass into the region with surface dewpoints well into the lower 70s throughout, and PWAts approaching 2.5". Not expecting a severe weather outbreak with the passage of the cold front, but scattered thunderstorms are possible. Showers taper off from west to east Thursday night, and end over southeast NJ and Delmarva by Friday morning. The front works its way east through the region on Friday, and skies clear out fairly rapidly during the day. Winds shift to the northwest in the afternoon, and a tight pressure gradient develops, with winds increasing to 15-20 mph with 20-30 mph gusts. The highest temperatures will occur just after midnight, and will fall throughout the day into the 50s and 60s Friday afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... NW flow persists Friday night between post-tropical Michael over Atlantic Canada and high pressure to the west. It will be a much colder night as a result with lows generally dipping into the 40s with even some upper 30s across the southern Poconos. For Saturday, forecast has become a bit trickier as the models have trended stronger with an upper level trough that will be swinging through during the morning into the early afternoon. Despite the cold advection pattern and limited moisture (both would favor drier conditions) this trough may be able to trigger enough lift for some showers Saturday morning. As a result, our forecast is a little more pessimistic than our model blend guidance in the gridded database. Also, we've increased the cloud cover significantly so expect mainly cloudy skies to start to the day before some late day sun. Temperatures have also trended cooler and expect highs only in the 50s to low 60s for most of the area. In fact the southern Poconos could remain stuck in the 40s. Conditions clear Saturday night as the trough exits and high pressure finally moves in. This will set up good radiational cooling conditions with lows ranging from the 30s in the southern Poconos and NW NJ to the low to mid 40s along the I-95 corridor and points south/east. For Sunday, the high will slide offshore with some increasing clouds through the day ahead of the next system as the pattern will be progressive. At this point though, still think the day should stay dry. Temperatures will remain cool but should be a few degrees warmer than Saturday's highs. Heading into the early to middle part of next week, forecast details become a bit less certain. However in the big picture, the pattern looks to remain fairly progressive with the next cold front along with an associated upper level trough arriving by Monday bringing the chance of showers. Some uncertainty though on how quickly this moves through as a wave could try to develop along the front which could keep conditions unsettled into early Tuesday before the next high pressure system arrives. This high pressure system should give a brief respite by late Tuesday before yet another system could arrive by next Wednesday. Temperatures look to be roughly around seasonal during this time period (Monday - Wednesday). && .AVIATION /02Z THURSDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...Mainly VFR through this evening though there could still be some brief MVFR cigs at KACY. Overnight, expect cigs to lower to MVFR as the next cold frontal system approaches. This should occur from west to east in the 6-9z time frame and there may also be some showers by morning. Winds generally southerly 5-10 knots. Thursday...Widespread rain and showers, heavy at times, with sub VFR conditions. Both cigs/visbys should be at least MVFR most of the day but expect some IFR cigs at times (especially in the morning) and IFR visbys at times (especially in the afternoon) in the heaviest showers. Winds increasing to SW around 10 knots with some gusts of 20-25 knots possible. Thursday night...Sub VFR conditions continue in heavy rain for KMIV/KACY as Michael passes by to the south. The remaining sites should see restrictions improving by the overnight behind the passing cold front. Winds may be quite variable for a time in the evening before becoming N/NW and eventually NW overnight increasing to 10-20 knots with higher gusts. Friday...Conditions become VFR for all sites with the big story being NW winds likely gusting 25-35 knots or even a bit higher through the morning before diminishing in the afternoon. Outlook... Saturday and Sunday...VFR overall. Northwest winds around 10 knots Saturday become light and variable at night, then becoming light southwesterly during Sunday. Monday...Sub VFR possible as the next frontal system arrives bringing the chance of showers. && .MARINE... Winds/seas should remain below advisory criteria tonight, with generally fair weather expected. There may be a few showers on Delaware Bay and the Delaware Atlantic coastal waters, but any of these would be spotty. Winds will generally be southerly or southeasterly 5 to 15 kts, with seas near or below 4 feet. Southerly winds increase late tonight, and then will reach SCA levels by Thursday morning. SCA now in effect for the ocean waters and Lower DE Bay for Friday, as southerly winds will increase to 15-20 kt with 30 kt gusts, and seas building to 3 to 5 feet. VSBYs will be restricted in heavy rain showers and scattered thunderstorms Thursday afternoon through Thursday night. Winds diminish Thursday evening, but ocean seas remain elevated. As a cold front passes through the waters on Friday, winds abruptly shift to the NW, and increase to 20-30 kt with 35-40 kt gusts on all waters. A Gale Watch is now in effect for all waters, mainly for Friday. Outlook... Friday night through Monday...Small Craft Advisory conditions could linger through Friday evening before winds/seas subside below this level by the overnight. The remainder of the weekend through early next week should see conditions below Small Craft Advisory. && .TIDES/COASTAL FLOODING... Two periods, and completely different hazards we are concerned about: First, models are depicting spotty minor tidal flooding with the high tide during the day on Thursday. Water levels have been slow to return to normal levels after our coastal flooding concerns this past weekend, thanks in large part to continued southerly flow. In addition, heavy rain is expected primarily tomorrow afternoon into Friday morning. This could exacerbate any tidal flooding issues. At the present, it looks like the heavy rain will be after the high tide on the oceanfront and lower Delaware Bay, so the threat for widespread tidal flooding in these areas is quite low. On the upper Delaware Bay and the Delaware River, high tide could be coincident with heavy rain. Since the nature of the flood event may be more fresh water than tidal, and in the interest of keeping the messaging simple, we will be highlighting the overall fresh water flooding threat in the HWO and flood watch, but no tidal flood products are anticipated at this time. Secondly, on Friday, expect strong northwesterly winds behind the cold front. This is a classic setup for blowout tides. However, at this time, no guidance is depicting blowout tides (though some does depict the low tide on Friday being below MLLW). We will continue to watch this however, and may have a better idea especially Thursday night when we start to see the base tide anomaly change with the wind shift. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch from Thursday afternoon through late Thursday night for PAZ070-071-101>106. NJ...Flash Flood Watch from Thursday afternoon through late Thursday night for NJZ008>010-012>027. DE...Flash Flood Watch from Thursday afternoon through late Thursday night for DEZ001>004. MD...Flash Flood Watch from Thursday afternoon through late Thursday night for MDZ008-012-015-019-020. MARINE...Gale Watch from Friday morning through Friday afternoon for ANZ430-431-450>453. Small Craft Advisory from 8 AM Thursday to 6 AM EDT Friday for ANZ431-450>453. Gale Watch from late Thursday night through Friday afternoon for ANZ454-455. Small Craft Advisory from 8 AM Thursday to 3 AM EDT Friday for ANZ454-455. Small Craft Advisory from midnight Thursday night to 6 AM EDT Friday for ANZ430. && $$ Synopsis...Fitzsimmons Near Term...AMC/MPS Short Term...MPS Long Term...Fitzsimmons Aviation...Fitzsimmons/MPS Marine...Fitzsimmons/MPS Tides/Coastal Flooding...