Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 251701 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 101 PM EDT Mon Sep 25 2017 .SYNOPSIS... High pressure over the Northeast will weaken a bit and lift to the north and east tonight through Tuesday. Meanwhile, Hurricane Maria will track to the north and will approach the eastern Carolinas on Wednesday before a cold front curves it out to sea on Thursday. Another cold front moves through the region on Friday. Surface high pressure and an upper trough digs into the East Coast for next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A rather quiet day in progress with mostly sunny skies and very warm temperatures. Readings have risen into the low/mid 80s in most areas. Highs should top out 4-6 degrees higher in most areas. These values are within a few degrees of daily records. Low clouds are reaching the ern NJ coast attm, but dissolving as they arrive over the warm land. Towards sunset, these clouds will tend to resume the NW motion.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Forecast becomes a little more interesting tonight, as onshore flow to the north of Maria begins to have more of an influence on sensible weather across the region. The 00Z RGEM is bringing in light showers to the far southern CWA late tonight (mostly offshore, but possibly into southern DE). The 00Z NAM Nest is at least suggestive of this (though far less aggressive), and there is marginal support from the latest WRF-ARW and WRF-NMM simulations. Some drizzle or light showers may occur as this deck moves inland, especially near the coast. Have kept mention of PoPs to account for this possibility, though any precipitation amounts should be quite light. Notably, forecast soundings do not moisten the atmosphere above an inversion around 975-950 mb quickly, and such a profile strongly favors drizzle versus showers. More likely is the increase in low stratus and potentially fog from east to west through the area tonight. Not completely sold on the fog potential -- model forecast soundings show an elevated inversion, which is strongly suggestive of stratus versus fog. However, the presence of a fog deck offshore now certainly suggests its possibility, so may need to include mention of this in the grids in subsequent updates. Meanwhile, farther west, skies should remain clear for longer, and this should promote the development of fog as winds relax and temperatures plummet to surface dew points. Have more widespread mention of fog in the grids tonight to the west of the Delaware River (mainly in more rural/valley locations), though kept coverage as patchy given antecedent dry conditions and the general overforecasting of fog the past few nights. Low temps are generally a blend of MAV/MET, with some incorporation of hi-res guidance to accommodate for the expected increased cloud cover overnight. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Impacts from Hurricane Maria of high surf, beach erosion, and a high risk for rip currents are likely for the DE and NJ coasts for most of the mid-week period. Tropical Storm force winds, however, should stay south and east of the area. High pressure weakens a bit and lifts to the north and east on Tuesday. Hurricane Maria tracks to the north and approaches the Carolina coast Tuesday through Wednesday. Outer bands of precip will lift to the north and may move into southern and eastern portions of the forecast area, but the high looks to be strong enough to keep most of the outer bands at bay. Will go ahead and lower PoPs a bit from previous forecast, and will carry slight chance/low chance PoPs for Tuesday through Wednesday. Northeast winds during this time will range from 5-10 MPH inland and 10-20 MPH along the coasts. This brings a cooler airmass to the region. Highs will range from the upper 70s to low 80s along the coast to the low to mid 80s most areas inland. On the western side of the Fall Line, highs may even get into the mid and upper 80s. A cold front passes through the region Wednesday night through Thursday. Mid-level shortwaves will pass well to the north, so without much upper level support, not expecting much in the way of showers. Will cap PoPs at slight chance inland to low chance along the coasts, mainly due to the onshore influence. This cold front will help curve Maria out to sea. It also ushers a much cooler airmass into the region, as highs drop by almost 10 degrees on Thursday. Highs range from the mid 70s to around 80, with cooler temps up in the Poconos. A secondary cold front will pass through the region Friday, and this ushers a much cooler airmass into the region with below normal temperatures for the weekend. Surface high pressure builds into the Eastern U.S., but this will also be accompanied with an upper trough for the weekend. This trough may result in some isolated showers, but the surface high should keep conditions dry for the most part. Highs should be in the 60s to around 70. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Another nearly cloud-free day is on tap with light northeast or east winds. A stratus deck may move from east to west slowly over eastern portions of the area tonight, affecting primarily KACY and KMIV, with MVFR/IFR conditions possible by or shortly after midnight with potential to reach the urban corridor near daybreak Tuesday. Meanwhile, fog should redevelop west of the urban corridor, especially after midnight, with coverage more widespread and VSBYs potentially reduced more frequently to MVFR/IFR categories. Outlook... Tuesday and Wedensday...Mostly VFR conditions expected. Scattered showers are possible, mainly at KACY. These showers may result in MVFR conditions if they pass over a terminal. NE winds 5-10 KT during this time, except 15-20 KT with gusts to 25 KT along the coast, including KACY. Wednesday night and Thursday...A cold front will bring a shift to northwesterly winds and a slight chance for showers. Otherwise, mostly VFR conditions are expected. Friday...Mostly VFR conditions expected.
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&& .MARINE...
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A fog bank is lurking offshore as of late this morning, though models have been too fast in moving this bank westward. Nevertheless, expect a slow westward trend today and tonight (though this should be tempered during the late morning and afternoon hours). Tonight, low stratus should encompass the marine waters, and there may be some fog as well with the accompanying visibility restrictions. Seas have been overforecast by 1-2 feet from model guidance, and this is expected to continue today. Thus, small craft advisory conditions have been slow to materialize so far on the Atlantic waters. Nevertheless, the trend in seas will be upward, with long- period (11-15 seconds) 3-6 ft southeasterly swells emanating from Hurricane Maria making for gradually rougher marine conditions. Small craft advisory for hazardous seas continues for the northern/central New Jersey waters but has been changed to a small craft advisory (from effects for both winds and seas) for the southern NJ and DE coastal waters (as winds will increase on Tuesday in advance of Maria; see the Outlook section below). Outlook... Tuesday and Tuesday night...SCA conditions for both winds and seas expected on DE and southern NJ ocean waters. Otherwise, SCA for Haz Seas for northern NJ ocean waters. Seas building to 9-11 feet. NE winds gusting to 25-30 KT over DE and southern NJ ocean waters. Wednesday...An SCA will likely be needed for the entire period on the ocean waters as elevated seas due to swells associated Hurricane Maria will be observed through this time. Seas will gradually build to 8-11 feet by Wednesday. Gusts above 25 KT will be possible especially on the Delaware Coastal waters Wednesday. Elevated waves will be possible at the mouth of the Delaware Bay. Otherwise, winds and waves should stay below SCA criteria on the Bay. Thursday and Thursday night...A cold front will bring a shift to northwesterly winds and gusts above 25 KT likely for part of the period on the Atlantic Coastal waters. In addition, seas will likely still be elevated due to swells from Maria. Friday...Winds and seas will be diminishing through the day, though it is uncertain how quickly they will diminish. Rip Currents... The rip current risk remains high as long-period southeasterly swells continue to build thanks to Hurricane Maria. Conditions should only deteriorate today, with swells expected to build slowly through the day. Given the observed rip currents this weekend along much of the NJ/DE surf zone, swimming is not recommended, especially in the absence of lifeguards/beach patrols. Dangerous surf conditions will continue for much of the new week. A HIGH risk for the development of dangerous rip currents is expected from Tuesday through at least Thursday. High surf conditions and beach erosion likely to develop Tuesday and Wednesday.
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&& .CLIMATE... High temperature records for today: ACY...91(1970) PHL...92(1970) ILG...93(1970) ABE...92(1970) TTN...92(1970) GED...92(2010 and 1970) RDG...92(1970) MPO...85(1970) && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Rip Current Risk through late tonight for NJZ014-024>026. DE...High Rip Current Risk through late tonight for DEZ004. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ452>455. Small Craft Advisory for hazardous seas until 6 AM EDT Wednesday for ANZ450-451. && $$ Synopsis...MPS Near Term...PO Short Term...CMS Long Term...MPS Aviation...CMS/MPS/PO Marine...CMS/MPS Climate...

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