Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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568 FXUS61 KPHI 250054 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 854 PM EDT Sun Sep 24 2017 .SYNOPSIS... High pressure will stay over our region tomorrow, before weakening Tuesday. Hurricane Maria will track northward over the Atlantic waters, approaching the Coastal Carolinas on Wednesday, then curving out to sea on Thursday as a cold front passes through the region. A second cold front may propagate through our region Friday into Saturday before a large area of high pressure builds over the Northeast. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... No big changes expected this evening to the forecast. Main challenge will be hourly temperatures for the next few hours as temperatures will drop sharply in some areas after sunset for a an hour or two, before a slower decline overnight. Otherwise, another nice night is expected with mostly clear skies and light winds. There was a little fog around the rural areas last night and the will probably be more fog in these areas tonight. We will keep the patchy wording in the grids as before. Low temperatures will drop into the low 60s north and mid/upper 60s elsewhere. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... High pressure will remain over the area Monday. It will be a little more humid as the onshore flow will continue. Skies will be mostly sunny during the day. High temperatures will be a little cooler than today, but still above normal for late September. Highs will be in the upper 80s in most areas. Winds will again be light from the E or SE. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
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Hazards: CFW-High risk rip currents, especially since swells will triple by late Tuesday (to around 9 feet), what we saw this afternoon and the period will be similar 13-14 seconds... resulting in an even more dangerous surf zone. CFW-SU.y HIGH SURF Advisory. May need to considered for Tue-Wed. One NWS schematic indicates the energy of a 13 second 10 foot swell can cause breakers to nearly 14 feet. While we probably wont forecast that high... forecasting closer to a 1 for 1 relationship, or in this case a 10 foot swell of 13 second period to equate to about a 10 foot beach breaker. There is little doubt that longer period swells break larger than a swell of similar height but much shorter period (those shorter ones are steeper but with less energy). Tuesday and Wednesday...Surface high is expected to weaken through this time, however not as quickly as shown with previous model runs. Therefore, trimmed back PoPs across eastern PA and NW NJ. However, kept a mention of showers across our Coastal Plains as we may have a few of the very outer rain bands of Maria near the coast. Based on the latest forecast track of Maria, all tropical storm force winds should stay well to the south of our region. Thursday...Models have generally trended faster with the cold front propagating through our region Wednesday night into early Thursday. In addition, there remains good model consensus that Maria will make the sharp ENE turn through this period heading much further out to sea. What that means for our region is that we should have breezy northwesterly winds behind the front. Models have backed off on precipitation chances with and just ahead of the front, so I lowered PoPs slightly, but given the moist marine layer that should be in place thanks to the onshore flow from the two previous days, think that showers are still possible. Friday through Sunday...Cooler air will settle in over the region. Temperatures through this period are likely to be near or slightly below normal (in stark contrast to the beginning of the week). One feature of note is a low digging southeast out of central Canada towards the Mid Atlantic Friday into Saturday. At the surface, this would mean a second cold front could arrive in our region early in the weekend. The previous run of the ECMWF showed a very amplified solution with a mid level closed low almost becoming cutoff over our region through the weekend. The 12Z run is much closer to the GFS solution showing a progressive pattern (albeit still closed low). This will be a major change from the large scale pattern we have now (trough over the western U.S. and ridge over the east), so hesitate to favor one solution over another given the large uncertainty. Thus, through this period, have gone with a blend of models and a slight chance of precip.
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&& .AVIATION /01Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. High pressure across the TAF sites tonight will keep good flying weather through the period. The only exception will be the possibility for some fog overnight mostly at the more rural locations. We have included a period with fog in the terminals except for KPHL and KPNE where chances of fog are lower. Once the fog diminishes Monday, more VFR conditions with mostly clr skies are expected. Winds will be light from the E or SE through Monday. Outlook... Tuesday and Wedensday...mostly VFR conditions expected. There is a chance for showers both days (if any showers move over a TAF site, MVFR or lower conditions are possible). Northeasterly wind up to 10 KT possible. At the coast, including KACY, northeasterly winds of 15 to 20 mph with higher gusts will be possible. 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. && .MARINE...
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While winds will remain light tonight and Monday, seas will increase slowly as the swells associated with the offshore tropical systems continue. Currently seas are around 3 to 4 feet, but should increase through the night to around 5 feet. On Monday, they should increase to 5 to 6 feet. We will continue with the marine flags (Small Craft for Hazardous Seas) as previously lined up. Fair weather tonight and Monday. Outlook... Tuesday and 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... We regret to inform that New Jersey recorded its record 8th rip current related fatality yesterday, and yet another within an hour of low tide. The period of record dates back to 1996. Many rescues today..despite swells only around 3-4 feet but the 13 second period from Maria is causing the formation of dangerous rip currents. They are transitory but powerful channels of seaward moving water, especially noticeable during the lower half of the tide cycle as water trapped behind the bars cuts a narrow channel and rivers swiftly seaward through the surf zone. Since no lifeguards are on duty...a phone call about a distressed swimmer can easily become a recovery. Why risk it? Also...rocks and jetties... no need to get knocked off the jetty by a breaking wave and put would-be rescuers in danger. VERY DANGEROUS SURF CONDITIONS CONTINUE THROUGH MUCH OF THE WEEK and these will worsen considerably by Wednesday. Please do not go swimming in the rough surf and stay off rocks and jetties. No need to put would- be rescuers in danger. Please follow the advice of local officials. If you must go in the surf, please only go in to ankle deep. As for the details each day: Monday...A HIGH risk for dangerous rip currents will continue through Monday. Tuesday and Wednesday...this is likely to be the most dangerous period of the week as we are expecting the highest swells due to Hurricane Maria. The threat for the formation of dangerous rip currents will be HIGH through this period. Thursday...rough surf is likely to continue, thus it is likely that the HIGH threat for the formation of dangerous rip currents will continue. Friday...swells should begin to subside resulting in a decreased risk for rip currents, though it is likely to at least start the day as a moderate risk.
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&& .CLIMATE...
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The following stations equaled their record for this date Allentown-92, Mount Pocono-85, Trenton-92, Wilmington-92. High temperature records for today ACY...92(2010) PHL...95(1970) ILG...92(2010/2017) ABE...92(1970/2017) TTN...92(1970/2017) GED...97(2010) RDG...95(1970) MPO...85(2010/2017) Monday 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) We will evaluate the monthly climate projection by 930PM.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Rip Current Risk through late Monday night for NJZ014- 024>026. DE...High Rip Current Risk through late Monday night for DEZ004. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Tuesday for ANZ450>455. && $$ Synopsis...Johnson Near Term...Robertson/O`Hara Short Term...O`Hara Long Term...Drag/Johnson 853 Aviation...Johnson/Robertson/O`Hara Marine...Drag/Johnson/Robertson/O`Hara Climate...853

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