Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 302235 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 635 PM EDT TUE AUG 30 2016 .SYNOPSIS...
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High pressure will move offshore tonight, then a cold front moves through our area Wednesday night. High pressure will build southeast into the Great Lakes and New England. Tropical depression nine, currently in the Gulf, is expected to move northeast tracking offshore over the holiday weekend with high pressure anchored to our north through early next week.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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The locally heavy showers that developed in southeastern New Jersey and southern Delaware have dissipated. As a result, a dry night is expected as weak high pressure retreats offshore. Radar imagery shows a well defined sea breeze nearly along the Delaware River as of 22z, with likely some enhancement from the earlier showers. This feature is expected to dissipate as it moves more inland. The daytime heating induced cumulus continues to thin and these will dissipate through early this evening. Some high clouds will stream across parts of the region at times well ahead of an upper-level trough in the Midwest and upper Great Lakes. The low-level moisture will increase some with a light onshore flow, and surface dew points will therefore creep up during the overnight hours. As we start this evening, there is quite the dew point gradient centered near the Delaware Valley. It is much drier along and to the north and west of this area, with dew points around 70 south and east. This increase in low-level moisture in combination particularly where rain occurred earlier can result in patchy fog overnight. The hourly temperature and dew point grids were adjusted based on the latest obs, then the LAMP/LAV guidance was blended in. This included showing warmer temperatures to start this evening across much of the area.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
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High pressure over northern New England continues to push offshore on Wednesday. Meanwhile, weak low pressure tracking across Canada will drag a cold front through the Ohio Valley and towards northern NJ in the afternoon. H5 trough with several embedded shortwaves will follow thereafter, approaching mainly the Poconos into northern NJ late in the day. For most of the day, the energy and support for showers and thunderstorms will occur north and west of our area, so slowed down the POP increase and carried slight chance to low chance across the northwestern zones toward late afternoon. In addition, Tropical Depression 8, currently just south of Cape hatteras, may strengthen to a Tropical Storm, but is forecasted to pass well to the southeast of the Delmarva before tracking into the western Atlantic waters. Highs on Wednesday will once again be 5-7 degrees above normal, with highs in PHL possibly touching 90 once again.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Wednesday night and Thursday: A cold front will approach the region from the northwest. Ahead of this front moisture will be advected into the region. Modeling may be to quick with the moisture advection, especially given the recent dry pattern. However, enough moisture and lift looks present along this front for the formation of a band of showers and a couple of thunderstorms to move from northwest to southeast across the region. A few heavy downpours would be possibile (PW ahead of front 1.5-1.75 inches). Strong to severe thunderstorms are not anticipated given both the GFS and ECMWF are only advertising a few hundred J/KG of CAPE ahead of this front along with a overnight event. Showers and isolated thunderstorms should end across the southern portions of the region during the day Thursday. QPF of a quarter to half inch seems reasonable as well, with the SREF, WPC and the WRF NMM/ARW models used for the QPF forecast. High temperatures Thursday will likely end up a few degrees below MOS guidance given the cloudcover with highs around 80 in most places. Thursday night through Tuesday: High pressure will build eastward into New England and remain in place or slowly shift east through early next week. Temperatures look to be several degrees cooler through the weekend, with a warming trend early next week. If it were just this high pressure system as a potential influence on our weather, sunny skies with a dry holiday weekend will occur. However, TD 9 is a potential factor as well. The GFS, GEFS, UKMET and Canadian models all have this feature slowly tracking up the coast, stalling it to our south or even turning back to the northwest. This would increase cloudcover, winds and the prospects for rain as you get closer to the coast. The ECMWF up till the 30/12 run has been fairly consistent with having TD 9 get carried out to sea with the trough which brings a cold front through on Thursday. Overall, a lot of uncertainty is present around the weekend time period. Given the building ridge this weekend the potential is present for this system to get trapped somewhere close to our region. However, will not commit fully to the new trend yet given it is only set of model runs. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR overall. MVFR ceiling at ACY is expected to dissipate through early this evening. Some local MVFR/IFR visibilities possible toward morning due to fog. Winds becoming mostly light and variable. Wednesday...Any local fog dissipates by 12z, otherwise VFR. South or southwest winds increase to 5-10 knots. A cold front will approach later in the day. It appears that much of the showers/thunderstorms remain to our north and west, however some may approach ABE and RDG after 21z. OUTLOOK... Wednesday night and Thursday: Mainly VFR, with some MVFR restrictions possibile in any heavier showers or isolated thunderstorms. Southwest winds around 10 knots shifting to northwest, higher gusts Thursday afternoon. Thursday night through Friday night: VFR. Northerly winds around 10 knots. Saturday and Sunday: Considerable uncertainty in this period of the forecast due to currently TD 9. If TD 9 stays offshore (currently most likely) VFR throughout with winds generally under 15 knots. Lower ceilings and higher winds if we see impacts from TD 9, KACY and KMIV have highest chances currently.
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&& .MARINE...
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Wave heights came close to 5 feet with long period swells, but going into tonight, wave heights will begin to subside, and will expect 3 to 4 ft seas through Wednesday. Cold front slowly approaches the waters late Wednesday. Water temps are generally in the 70s, which is above normal. OUTLOOK... Thursday through Sunday: Seas gradually building heading into the weekend. Seas of a couple of feet and northerly winds at or under 15 knots through Friday. Considerable uncertainty with how high the seas get in relation to the track of TD9 for the weekend. Seas right now look to be at or above SCA criteria from Friday night from Sunday. Northeasterly SCA gusts are possibile in this timeframe as well. RIP CURRENTS... The 3 to 4 foot long period swells and an onshore flow continues, therefore the rip current risk remains at moderate. For Wednesday: Wave heights may slowly decrease during the day, but with 12-13 second period swells, will continue with the moderate risk of dangerous rip currents. A Beach Hazards Statement remains in effect through Wednesday that continues to highlight this hazard. Thursday: Rip current risk probably eases back to low. Friday-Monday: Rip current risk increases with cool boundary layer wind transfer as high pressure develops to our north, with an ensembled fairly extensive broad easterly fetch developing south of New England. Likely to be moderate or higher depending on the track of TD9. In terms of safety, follow the advice of local lifeguards who will be observing the waves and swimmers. There may be some beach closures, all dependent on the reality that develops. This is not a time to swim on your own without lifeguard presence. Additionally, waders are cautioned not to turn their backs to the waves when coming out of the water. Wave knock down can result in upper torso injury (dislocations/spinal cord injuries).
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&& .TIDES/COASTAL FLOODING...
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Some minor tidal flooding is possibile late this week and the weekend with the high tide cycles. However, this is highly dependent on the track of TD 9. A track closer to the coast would increase the threat.
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&& .CLIMATE... This section is up to date through 3 AM Today-Tuesday August 30. A top 4 warmest August appears assured most of our forecast area with record monthly warmth likely at PHL. A top 3 warmest June-July-August for Philadelphia, Allentown and possibly Atlantic City. Philadelphia will establish its warmest August on record (dating back to 1874). More than 4 degrees above normal. This Philadelphia August ranking includes our forecast temps (SFT specific values) through the 31st. The 30 year normal is 76.6 Records date back to 1874. 1. ~81.0 2016 2. 79.9 1980 3. 79.8 2001 and 1995 Regarding whether August can tie its record of 17 90F days. Its possible. Today is the critical day for extending the heat wave. The record of 17 was set in 1995. The mean for the month is only 5. Tomorrow reaching 90 at PHl looks to be relatively easy. Allentown will rank #2 warmest August. Records date back to 1922. Normal is 71.7 and we are projecting a positive departure of around 5 degrees. 1. 78.2 1980 2. ~76.6 2016 3. 76.0 1937 Atlantic City records date back to 1874. The August monthly normal is 74.4 and we`re projecting a positive departure of nearly 4 degrees. As it stands, Atlantic City will rank #1 warmest August with very little chance of slipping to #2. The forecast and climate for Atlantic City has greater variability than Allentown and Philadelphia due to proximity to water on sea breeze days and notable radiational cooling on some nights. 1. 78.2 2016 2. 77.9 2005 3. 77.1 2009 Seasonal: This summer 2016 for Philadelphia will probably be the 2nd warmest June-July-August (JJA) in the period of record dating back to 1874. 1. 79.6 2010 2. 78.8 2016 3. 78.6 1995 4. 78.3 1994 Allentown seasonal avg is projecting 75.0 or a ranking of around #2 in the por. 1 75.3 1949 2 75.0 2016 3 74.6 2005 and 1980 Atlantic City seasonal average is projecting 75.8...4th warmest in the por. 1. 77.5 2010 2. 77.0 2011 3. 75.9 2005 4. 75.8 2016 5. 75.5 2008 90 degree days through the 29th. season mean Aug Aug Aug Season mean rer rer ABE 33 17 12 4 16-1980 41-1966 ACY 28 10 11 3 11-2010 46-2010 PHL 39 21 15 5 17-1995 55-2010 ILG 33 20 14 5 23-1895 59-1895 Rainfall: Some uncertainty exists regarding additional rainfall in August, so this part of the climate is stated with caution. Presuming no further measurable rain this month of August...the current ACY value of 1.10 would rank the 6th driest August on record, after a 6th wettest July. For Philadelphia, the June-August seasonal total of 7.45 inches is so far, the 12th driest summer...again this presumes no further measurable rain in August. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...Beach Hazards Statement through Wednesday evening for NJZ014- 024>026. DE...Beach Hazards Statement through Wednesday evening for DEZ004. MD...None. MARINE...None. && $$ Synopsis...Gaines Near Term...Gorse Short Term...Gorse/MPS Long Term...Gaines Aviation...Gaines/Gorse Marine...Gaines/Gorse/MPS Tides/Coastal Flooding... Climate...

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