Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 282151 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 551 PM EDT Wed Sep 28 2016 .SYNOPSIS... An area of low pressure will move across the Ohio Valley and combine with another low across the central and southern Appalachians Thursday into Friday. A cold front will cross the region around Sunday. High pressure is then expected to build to our north into early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... FFA issued where this mornings unexpected heavy rain expanded an area where it will take only 3-4 inches of rain in 6 hours to cause flooding. PWAT up near 2 inches, significant e-se 850 mb inflow and expected tstms was the reasoning for the FFA. Confidence on 6" occurring between 6P today and 6P tomorrow is low but it is possible. otherwise, bands of showers and drizzle tonight, especially late and especially e PA and the Delmarva. nice waa pattern (aloft) tonight. fcst basis: 50 50 blend of the 12z/28 gfs/nam mos guidance. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... showers, drizzle. some of the rain heavy. most of the heavier rain should be Delmarva/se PA. its possible drying from the northeast could invade NNJ and prevent little if any rain in the afternoon. cool. ne wind gust 20-30 mph....possibly gusty 40-45 mph along the immediate coast of NJ and near Lewes DE. fcst basis: a 50 50 blend of the 12z nam/gfs mos guidance. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... Unsettled weather continues for the first portion of the extended fcst, with some improvement by the end. A large area of upr lvl low pres will be located to our s and w at the start of the extendd pd. This low will spin in place then gradually retrograde to the Grtlks and sern Canada by the weekend. At the sfc, an area of low pres will be located over the midwest, with high pres to the ne over New Eng and sern Canada. The sfc features will keep a persistent moist nely flow over the area at the sfc with swly flow aloft. As the sfc low moves by to the nw, one pd of rain is expected and as several other s/wvs rotate thru the upr low several other pds will occur. As is usually the case with upr lows, it will not rain the whole time. It will be cloudy and dreary with pds of rain. The mdls differ on which times will be rainy and where those rainy pds will occur. For example on Friday, the GFS is mainly dry, while the ECMWF is fairly wet and the NAM somewhere in the middle. Have tried to make adjustments to pops where there was a decent signal in the mdls, but these times were limited and overall confidence on which pds will be rainy are low. By Sat and Sun, the upr low moves nwd into the Grtlks area and begins to weaken and fill. Overall precip chcs shud decrease. However, guid today is wetter than it was yda and once again it will depend on individual w/wvs. Sat shud be wetter than Sun with precip chcs decreasing with each passing day. Some guid now even wants to linger precip chcs into Mon until the upr low finally passes to our e and high pres builds in behind it. By Wednesday, all eyes turn to the tropics and any potential impacts from what is now Tropical Storm Matthew later in the week. Please see NHC advisories for updates. && .AVIATION /22Z WEDNESDAY THROUGH MONDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...MVFR cigs probably becoming more widespread. scattered showers briefly limit visibility to 3 to 5 mi. ne wind gust 15-22 kt. Tonight and Thursday...MVFR cigs variable down to IFR conds in areas of showers, drizzle, stratus and fog. Some of the rain may be briefly heavy and there may also be a tstm, (the thunder mainly PHL south) but for now the tstm is not in the TAF. ne-e wind gusty 15-20 kt tonight and 20 to 30 kt Thursday. OUTLOOK... Thu night-Fri...A prolonged period of MVFR or IFR conditions with pds of RA expected to affect the TAF sites through the period. E to Ne winds are expected to gust 20-25 knots for much of the area, especially KMIV and KACY. Moderate confidence. Fri night-Sun...Some improvement, possibly to VFR by Sun. SHRA remain psbl. Moderate confidence. && .MARINE... Gale warning issued with at least two surges of potential 35 kt gusts expected, one early Thursday and the more extensive probably late Thursday afternoon into Thursday night. The Gale supersedes the SCA and we keep the product simple by using the higher priority warning. Seas may build higher than 11 ft at 44091 but this is a forecast start for now. OUTLOOK... Thursday night...Gale warning in effect early, will likely need to be extended. Fri...Gale wind may remain across the northern half of the coastal waters. SCA may be needed elsewhere. Fri night-Sat...Wind expected to drop below SCA, however, seas will likely remain above 5 feet thru the pd. Sat night-Sun...Wind and seas expected to drop below SCA levels and no marine flags anticipated. Rip Currents... There continues a moderate risk for the formation of dangerous rip currents today as per a recheck of the ene sustained wind ~18kt and dominant 4 second short period swell. Thursday: The probability for the formation of dangerous rip currents is at least moderate to perhaps high. && .TIDES/COASTAL FLOODING... A persistent onshore flow is expected for the rest of the week into the weekend. The strongest winds are expected Thursday through Friday. Tides levels are forecast to increase through this period, and we should reach minor coastal flood levels Thursday evening/night high tide cycle for many of the coastal locations. This per ETSS, SIT modeled guidance and local in house program. For Lewes and Reedy point we ran a 1 ft departure this eve, 1.4 tomorrow morning with ene wind gusts around 30 kt and pres at 44009 of 1022MB (a bit high for a coastal flood event where the astro tide is not extreme). The result is marginal exceedance of the threshold for the Thursday evening high tide cycle of roughly .1 to .8 feet. All of this will be reevaluated by the subsequent shifts to determine confidence for a cf advisory issuance. we just are not sure yet what our storm tide will be the next two high tide cycles and we still have opportunity to adjust the max wind gusts at high tide and in the preceding hours. Usually, lower pressure than 1022mb is more favorable for boosting the surge. However, a notable easterly gradient could be enough to force the minor coastal flood event. && .CLIMATE...
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September will be/is a top 10 warmest month through most of our forecast area, for the 3rd consecutive month! Also September will be/is enjoying a second consecutive top 5 warmest month in the period of record for PHL and ABE. We`ve run the actual numbers through the 28th, then added the forecast high/low for 29th and 30th. Philadelphia: Expect a 73.8 degree average or about 5 degrees above the monthly normal of 69.1. This will be a #4 or #5 warmest September on record for Philadelphia. Philadelphia September average temperature rankings 75.4 -1881 74.5 -2015 74.1 -1931 74.1 -1930 73.8 -2005 and 2016 #4 (small chance PHL avg will be 73.7 or #5 ranking) 72.9 -2010 72.9 - 1921 Philly ranked #7 warmest July followed by a warmest ever August in the POR dating back to 1874. Atlantic City: Expect a 71.2 degree monthly average temperature, or 4 degrees above the monthly normal of 67.2. This would equate to an 8th warmest September in the period of record dating back to 1874. Atlantic City recorded a #7 warmest July and then a warmest ever August. 73.3 - 1961 72.8 - 1881 72.3 - 1931 and 1930 71.7 - 1921 71.6 - 2015 71.5 - 1933 71.3 - 2005 71.2 - 2016 #8 71.0 - 2010 70.6 - 2011 and 1906 Allentown: Expect a monthly average of 69.4 degrees, or 5.5 degrees above the monthly normal of 63.9 and a 4th warmest September on record. Allentown ranked 8th warmest July and #2 warmest August in the period of record. 70.8 - 1961 70.3 - 1980 69.7 - 2015 69.4 - 1931 and 2016 (small chance Allentown will rank #5 at 69.3 degrees) 68.7 - 2005 Daily rainfall records for September 29 where there is maybe a small chance of exceeding: PHL 1.87 1963 ILG 1.97 1963 GED 1.35 2015 RDG 3.55 1934
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...High Rip Current Risk through Thursday evening for NJZ014- 024>026. DE...High Rip Current Risk through Thursday evening for DEZ004. MD...Flash Flood Watch through Thursday afternoon for MDZ008-012- 015-019-020. MARINE...Gale Warning from 4 AM Thursday to 2 AM EDT Friday for ANZ430- 431-452>455. Gale Warning from 4 AM Thursday to 6 AM EDT Friday for ANZ450- 451.
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&& $$ Synopsis...Drag/Nierenberg Near Term...Drag Short Term...Drag Long Term...Nierenberg Aviation...Drag/Nierenberg Marine...Drag/Nierenberg Tides/Coastal Flooding... Climate...551P

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