Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 241429 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1029 AM EDT Sun Sep 24 2017 .SYNOPSIS... High pressure entrenched over the Northeast gradually builds to the north and east through the middle of the week. Meanwhile, Hurricane Maria will track to the north over the western Atlantic waters and will approach the Carolina coast on Wednesday. A cold front moves across the East Coast on Thursday and curves Maria out to sea. High pressure returns for the end of the week, and then low pressure may impact the region late in the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A couple minor adjustments to hourly temperatures and dew points were made at mid-morning. Previous ideas for the near term describe it well and are included below. Strong midlevel ridging will continue to move slowly eastward into the Northeast today. Result will be very warm temperatures in an environment of strong subsidence and clear skies. With abundant diabatic heating from insolation, today`s maximum temps should be a couple degrees warmer than those seen yesterday. Guidance was too cool yesterday, by several degrees in some locations. Given a similar environment today, was on the high side of guidance (and in some cases, exceeded all guidance) for temperatures this afternoon. There may be a few limiting factors for temperatures getting too far out of hand (i.e., well above guidance). The first is that winds will be a little weaker today, so boundary-layer mixing will be somewhat more limited. As such, surface dew points may not mix out to the degree observed yesterday, and this may temper near-surface heating to some degree. Additionally, the component of the wind should be more easterly today, which may temper warming via advection from a cooler source of air and will reduce the effects of downsloping. These factors were enough for me not to go well above guidance, but the current forecast may be too conservative should these factors prove to be overestimated. As far as records are concerned, think most of them are safe, especially Philly`s and Georgetown`s. Wilmington`s 92 and Mount Pocono`s 85 are at least plausible, but the current forecast is a couple degrees shy in both locations. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... Main forecast concern overnight is fog formation. Dew points will continue to creep upward, and with clear skies and calm winds thanks to ridging parked near or over the area, temperatures will likely decrease sharply after dark. Latest guidance is more aggressive with fog formation overnight (both in terms of areal coverage and persistence) compared to the past couple of nights. Included mention of patchy fog in the grids for most locations outside of the urban corridor. Used a blend of MAV/MET/ECMWF guidance for lows tonight. Forecast temps are expected to be in the low 60s in the southern Poconos to near 70 in the urban corridor. For hourly temperatures, incorporated 2-meter temperatures from a blend of higher-resolution guidance, given the rather poor performance of statistical guidance the past couple of evenings as temperatures begin their nocturnal decline. && .LONG TERM /MONDAY THROUGH SATURDAY/... Surface high pressure over the area on Monday weakens and lifts to the north and east on Tuesday. Temperatures remain well above normal with highs ranging from the low 80s along the coasts and in the Poconos to the mid and upper 80s for most of NJ, SE PA, and the Delmarva, and around 90 for the I-95 corridor. By Tuesday, winds take on more of a NE flow and winds increase to 10-15 MPH. This ushers a cooler airmass into the region, and highs will be about 10 degrees cooler than Monday. With onshore flow and some weak mid- level shortwave energy passing through the region, there may be some showers, possibly a thunderstorm, Tuesday afternoon and evening. Meanwhile, Hurricane Maria continues to track northward and approaches the Carolina coast on Wednesday. High pressure should be strong enough to keep Maria suppressed to the south, and then a cold front passing through the East Coast should take Maria out to sea on Thursday. Some outer rain bands associated with Maria may lift into the region during this time, but there is a better chance for showers and possible thunderstorms with approach and passage of the cold front. Tropical Storm force winds also should stay south and east of the region. Tide levels are running low since we are in between tide cycles, so the chances for minor coastal flooding are low at this time as well. Autumnal weather builds into the region to close out the week. Highs will be in the low 70s Friday, and then into the upper 60s to around 70 over the weekend. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR through tonight. Light/variable winds will become northeasterly around or below 10 kts during the day, veering to more southeasterly during the afternoon, especially near and east of the urban corridor. Winds should become light/variable again tonight. Few or no clouds are expected today. Some patchy fog may occur early this morning and again tonight, with chances tonight a little higher than the previous couple. A fog bank may also approach the New Jersey coast late tonight. However, no sub-VFR fog is mentioned in the TAFs at this point, as uncertainty in coverage/persistence is too high for inclusion. Outlook... Monday...VFR conditions are expected. Tuesday and Wedensday...Mostly VFR conditions expected, but there is a chance for showers and possibly a thunderstorm both days. Showers could produce brief MVFR or lower conditions. NE winds 10-15 KT, higher at KACY and possibly KMIV. Thursday...A cold front will bring a shift to northerly winds and a slight chance for showers. Otherwise, mostly VFR conditions are expected. && .MARINE... Small Craft Advisory for hazardous seas will remain in effect for the southern NJ and DE coastal waters, and has been reissued for the northern/central NJ coastal waters beginning at 4 pm this afternoon. Seas are generally around or just below 5 feet currently, but are expected to build slowly through the day. There will be a bit of a lag off the coast of northern/central NJ, but all Atlantic coastal waters should have seas greater than 5 feet by the evening hours. Winds will remain well below advisory criteria through the period. Long-period easterly to southeasterly swells will continue today, and there may be considerable chop from the combined swells of what remains of Jose and Hurricane Maria. One concern tonight is the potential for a fog bank to move westward into the coastal waters of the Atlantic. A rather large fog bank has persisted overnight well offshore, but has moved into far eastern Long Island and the adjacent waters. Latest guidance suggests this will advance farther west tonight, and given that surface flow will have a more easterly component today/tonight, this seems reasonable. Included mention of areas of fog tonight, mainly for locations away from the immediate coast. Confidence is not particularly high, but this may promote fairly widespread visibility restrictions should this threat materialize. Outlook... Monday through Wednesday...A prolonged SCA will likely be needed due to increasing seas due to swells associated with Hurricane Maria. Seas will gradually build to 8-12 feet by Wednesday. Gusts of 25-30 KT are possible, especially on the Delaware Coastal waters, Tuesday and 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...A cold front will bring a shift to northwesterly winds and gusts above 25 KT likely on the Atlantic Coastal waters. In addition, seas will likely still be elevated due to swells from Maria. Rip Currents... Today...Observations indicate longer-period swells are occurring on the coastal waters, with 8-10 second northeast swells from Jose being overcome by 12-16 second southeast swells from Maria. Wave heights will increase (albeit slowly) today and tonight. With yesterday`s observations suggesting rip currents were prevalent, today`s conditions are not expected to be any better and will likely get worse by late afternoon into the evening. As such, the risk of rip currents has been upgraded to high for today. Dangerous surf due to swells emanating from Hurricane Maria will likely result in a high risk for the development of dangerous and life threatening rip currents from Monday through at least Thursday. && .CLIMATE... Here are the records highs for today and Monday. Today ACY...92(2010) PHL...95(1970) ILG...92(2010) ABE...92(1970) TTN...92(1970) GED...97(2010) RDG...95(1970) MPO...85(2010) 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) && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Rip Current Risk through this evening for NJZ014-024>026. DE...High Rip Current Risk through this evening for DEZ004. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT Monday for ANZ452>455. Small Craft Advisory for hazardous seas from 4 PM this afternoon to 6 PM EDT Monday for ANZ450-451. && $$ Synopsis...MPS Near Term...CMS/PO Short Term...CMS Long Term...MPS Aviation...CMS/MPS Marine...CMS/MPS Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.