Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 170144 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 944 PM EDT Sat Sep 16 2017 .SYNOPSIS... High pressure gradually builds to our north and east into Monday. All interests in coastal areas of New Jersey and Delaware should follow the forecast of Hurricane Jose as it moves northward off the mid-Atlantic coast, probably passing well east of New Jersey Tuesday into Wednesday. High pressure is expected to settle back down into our area late in the week, behind the departing Jose. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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930 pm update: With weak steering flow, a moist/moistening atmosphere, and small-scale lift via sea/bay breezes/interactions, isolated to scattered slow-moving convection ended up being quite impressive late this afternoon and evening. Most places were bone dry, but the few that saw rain instead saw buckets. Philly International Airport recorded over 2.5 inches of rain in an hour this evening, and almost 2 inches of rain fell in Morristown as well. Received a couple of poor-drainage/urban flooding reports, but given the small areal coverage of the intense precipitation, impacts were reasonably subdued, fortunately. Showers are stubborn to dissipate to the west of Philly, and slight chance PoPs continue here for the next couple of hours. Attention then turns to the potential for low clouds/fog later. Most recent guidance is quite aggressive in the approach and/or development of stratus and/or fog after midnight. Latest infrared satellite imagery is showing a westward push (albeit slow) to the deck off the coast. Current grids have all of this in hand, and did not modify the forecast for this update. However, more updates may be needed later this evening as the details regarding stratus/fog development become clearer.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... A similar setup for Sunday as some ridging occurs across the Northeast, although a weakness still exists as a trough aloft remains across our region. Given the lighter flow, stratus and/or fog will dissipate during the morning although this may be slower along the coastal areas (assuming it is in place to start). Once any fog and/or stratus dissipates, we should have a similar day compared to Saturday with cumulus development occurring by late morning. Given the onshore flow, this may leave the coastal locales with more sunshine compared to inland during the afternoon (assuming any stratus/fog dissipates). Once again some showers cannot be ruled mainly in eastern Pennsylvania to northern New Jersey where terrain should assist in some development. We are not expecting much coverage given a lack of overall forcing and flow, and again should be low-topped and therefore left out a thunder mention. We continued with some low mentionable PoPs during the afternoon. High temperatures are mainly a blend of MOS and continuity. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... The main story remains Hurricane Jose and its pass off our coast next week. All of that follows shortly. Temperatures: Calendar day averages this 6 day period should be close to 9 degrees above normal the rest of this week and continue warmer than normal for possibly another week beyond that. The monthly negative departure should be virtually erased by next weekend and at that time monthly averages should be warming above normal. Forecast basis: 50 50 blend 12z/16 GFS/NAM MOS Sunday night-Mon night. Then the 12z/16 MEX MOS guidance was used for Tuesday with TCM wind tool "checked" but not used as an overlay on the sustained wind since TCM34 kt winds were a few NM east of our waters. Thereafter, the 15z D4-8 WPC grids for Wed-Sat. The dailies... Sunday night...nearly calm with any daytime showers probably dying out at sunset. Stratus and fog may become widespread late at night. Monday through Wednesday...Please see the forecast discussion from the National Hurricane Center for the latest details on the forecast track of Hurricane Jose. For our area, we are still looking at a track with the center passing 200-250 miles off shore, though still close enough for impacts to our region. At this point, we are expecting most of the impacts on Tuesday. This portion of the AFD indicates forecast anticipations. We will note where expectations are solidly categorical and where there is greater uncertainty. Sundays AFD`s and products will probably have some hazard issuances but we`re meshing the anticipations of our national centers and the WFO`s in a manner that will have coherent messaging. We should know considerably more at this time tomorrow about impacts from Jose and if they will be significant. Storm track looks pretty well clustered but western fringe of the 34 knot and 50 knot sustained wind envelope will ultimately determine the NJ and DE impacts. Confidences in those winds are expressed through the NHC wind probabilities. What is likely from this system in our waters and adjacent nearby shores. 1) HIGH SURF (10-15 foot seas) and HIGH risk dangerous rip currents...mainly Monday night Tuesday night. Confidence: above average. 2) Tidal flooding. A 1 to 2 foot storm surge at the times of high tides Monday evening through Tuesday evening. Confidence on a 1 foot surge is above average. Confidence on a 2 foot or slightly higher storm surge for Tuesdays Atlantic coast high tide cycles and possible moderate coastal flooding is, below average. So minor coastal flooding likely but anything more than that is below average confidence. Greater uncertainty below.. 3) Tropical sustained 34 knot wind gusts. Possible, mainly in the coastal waters. Confidence as expressed by the NHC 34 knot wind probabilities...is a little less than average. However, it will be close and 34 knot gusts are probable but the somewhat stronger sustained wind of 34 kt is less confidently assessed and stated. Nevertheless we expect a breezy Tuesday and possibly Wednesday over our area with gusts at least 25-30 mph. 4) Heavy Rain: Current track keeps the heavy rain off shore on Tuesday, with our area only seeing the outer rain bands. However, any additional rain at the shore near or shortly before a high tide could exacerbate coastal flooding. Finally, Thursday-Friday-Saturday...Most of the operational models depict a high amplitude ridge beginning to build over the region through this period, but it remains uncertain how quickly this will build. In addition, if it develops far enough north, we could be in a on shore low level flow regime for our area, tempering any warming trend due to the increasing thicknesses. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tough evening for KPHL, with an isolated but intense shower dumping 2.5 inches of rain in an hour. Showers have drifted west and should dissipate by midnight or so. Question then becomes development of sub-VFR CIGs/VSBYs. Latest guidance is strongly suggestive of at least one of the two, and possibly both, occurring. Given locally heavy rain today, lower VSBYs certainly plausible. Low stratus from the ocean is also expected to move in overnight. Expect a lengthy period of IFR conditions between 06Z and 12Z, and possibly occurring somewhat before/after this time range. Slow improvement is expected during the day tomorrow, but confidence in timing is low. Winds should be light/variable tonight with a predominant east direction tomorrow (under 10 kts). Outlook... Sunday night...VFR to start, then IFR stratus-fog should develop late at night in light northeast surface wind...especially e PA and nw NJ. Monday...IFR cond improve as cigs lift to VFR sct-bkn aoa 3500 ft during the afternoon except possibly MVFR cigs during the aftn along the coast. Gusty northeast wind ~ 15 kt. Monday night-Tuesday...Expect conditions to deteriorate to MVFR or lower along the coast with VFR cigs elsewhere. Gusty northeast winds much of the region, with KACY having the highest risk of gusts above 30 KT. Wednesday...Becoming VFR with decreasing north to northwest winds... gusting 15-20 kt. Thursday...VFR. Light north wind.
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&& .MARINE...
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930 PM update: Seas are running around 3-5 feet this evening and are expected to continue rising slowly. Current advisory looks OK. Nearshore fog still expected through the overnight hours. Will be watching closely to determine if any advisory is needed. The winds are expected to be well below Small Craft Advisory criteria through Sunday. However, swells are expected to gradually build through Sunday due to distant Hurricane Jose. This should get seas into the 5-6 foot range through Sunday and therefore the Small Craft Advisory for Hazardous Seas goes into effect early this evening for the ocean zones. Some locally dense fog is possible later tonight and early Sunday morning, mainly nearshore. Outlook... Sunday night...SCA seas for the Atlantic waters. Monday through Wednesday...Tropical storm conditions will be possible Tuesday. However, even Monday, winds may be above SCA criteria (~25 kt) in advance of Hurricane Jose approaching from the south. Although winds will begin to diminish Wednesday, it will take time for seas to subside. A tropical storm or gale related marine hazard may issue sometime tomorrow...all dependent on internal assessment of the wind fields. Rip Currents... High risk of rip currents is expected beginning tomorrow morning and will likely continue through midweek, as long-period swells from Jose reach the area. Rip current statement was issued earlier. Swimming at the beaches is not recommended the next few days.
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&& .TIDES/COASTAL FLOODING... Coastal flooding is possible with the high tide cycles Monday through Tuesday night due to the passage of Hurricane Jose. A prolonged period of east to northeast winds will allow water to pile up along the shores. In addition, there is a new moon on Wednesday, September 20, so astronomical tide levels will be running high. Depending on how close Jose tracks to the coast changes how significant the coastal flooding will be. As of now, minor coastal flooding is likely with the high tide cycles from Monday afternoon through Tuesday night. If Jose tracks closer to the coast, then widespread moderate coastal flooding will become more likely. If the timing of Jose slows down, then high tide cycles on Wednesday may be affected as well. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...High Rip Current Risk from 8 AM EDT Sunday through Sunday evening for NJZ014-024>026. DE...High Rip Current Risk from 8 AM EDT Sunday through Sunday evening for DEZ004. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Monday for ANZ450>455.
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&& $$ Synopsis...Drag Near Term...CMS Short Term...Gorse Long Term...Drag Aviation...CMS/Drag Marine...CMS/Drag Tides/Coastal Flooding...Staff

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