Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 282259 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 659 PM EDT Fri Jul 28 2017 .SYNOPSIS... An unseasonably strong low pressure system will organize over Delmarva tonight, and setup anchor off the middle Atlantic coast through Sunday, finally moving out to sea on Monday. Meanwhile, high pressure in the upper Mississippi Valley will settle over the mid Atlantic on Wednesday. A slow moving cold front is expected to traverse our region on Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Low pressure was developing over Virginia this evening. The low is forecast to strengthen as it moves to the Delmarva coast around daybreak. The area of rain showers associated with the system will continue to consolidate this evening across northeastern Maryland, Delaware and southern New Jersey, and it will likely expand to the north. The northern edge of the area of rain showers is anticipated to reach the Poconos and northern New Jersey late tonight. A swath of heavy rain is forecast overnight across northeastern Maryland, Delaware, southeastern Pennsylvania and southern New Jersey. Rainfall totals of 1.5 to 3 inches will be common with locally higher amounts of 4 to 5 inches expected, especially on the upper Delmarva and in southern New Jersey. As a result, the Flash Flood Watch remains in place. We will continue to mention scattered embedded thunderstorms through about midnight. The wind should favor the east and northeast overnight around 5 to 10 MPH. Minimum temperatures are expected to be mostly in the 60s. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Low pressure off the southern NJ coast lifts north and east on Saturday, followed by a secondary low south of the Delmarva. Wrap-around rainfall will retrograde back towards the mainland Saturday morning and into Saturday afternoon, and an additional 1/2 to 3/4" inch of rain possible where the heaviest rain will fall tonight. Gusty winds develop in the afternoon as a tight pressure gradient forms between the departing low and high pressure building in from the north and west, as well as with a 30-40 KT LLJ passing through. Showers will slowly taper off over southern portions of the CWA by late afternoon. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Improving weather expected Sunday with fair weather in the Monday through Tuesday period. With all the recent rainfall, patchy fog is possible each morning Monday into Wednesday. Diurnal showers and thunderstorms are possible on Wednesday, mainly northwest of I-95. With the approach of the next front, showers and thunderstorms are more likely Thursday into Friday. Temperatures will moderate through the week to seasonal levels. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Generally VFR conditions initially, but MVFR CIGs will overspread the terminals this evening as low pressure approaches from the south. Showers will begin to impact mainly southern terminals (KPHL/KILG/KMIV/KACY) this evening with heavy rain. As the low slowly tracks to the north and east tonight, widespread moderate to heavy rain will impact the terminals with IFR, possibly lower conditions. LIFR conditions probable at KILG, KMIV, and KACY late tonight through Saturday morning. Showers gradually taper off Saturday morning, with VFR conditions possible at KRDG by 18Z, but sub-VFR conditions in showers will persist at KMIV/KACY, and possibly KILG/KPHL. Light winds tonight become E-NE, and will increase to 10-15 KT west of I-95, and will be 15-20 KT with 20-30 KT gusts at KACY/KMIV. OUTLOOK... MVFR due to low clouds may linger at ACY and MIV into early Saturday night. Looking ahead, there is a low probability of MVFR in a -SHRA on Wednesday, mainly at ABE and RDG. Otherwise, VFR conditions are expected through Wednesday. Winds Saturday night into Sunday will generally be northeast at 10 to 15 knots with gusts up to 20 knots. Northeast winds are expected to continue on Monday at 5 to 10 knots, then should become variable on Tuesday, 10 knots or less. A southwest is anticipated to become established by Wednesday. && .MARINE... NE winds increase to 10-15 KT this evening, and then become 15-20 KT with 20-30 KT gusts on all waters after midnight tonight. Will hoist a SCA for all waters for the late night hours. During the day Saturday, as low pressure passes to the north and east, a tight pressure gradient develops, and can expect Gales on the ocean waters. Will convert Gale Watch to a Gale Warning through late Saturday night, but not expecting widespread Gales until Saturday afternoon. Gusts on the ocean will range from 35-40 KT. On DE Bay, will carry the SCA through Saturday night as wind gusts will range from 25-30 KT, and not expecting frequent and widespread Gales on the Bay. Seas on the ocean will build to 6-9 feet on Saturday. OUTLOOK... A Small Craft Advisory (SCA) is in effect for all of Delaware Bay through 9Z Sunday. A Gale Warning is in effect for the NJ and DE Atlantic waters through 6Z Sunday, when Northeast wind gusts in excess of 34 knots are likely. Seas in this time frame will also range from 7 to 10 ft on the ocean. Thereafter, frequent northeast wind gusts to 25 knots are expected through Sunday, and residual 5+ foot seas may liner into Sunday Night. Therefore, a SCA will likely be needed for the NJ and DE Atlantic waters through at least Sunday. Looking ahead to Monday through Wednesday, sub-SCA conditions are anticipated. RIP CURRENTS... A moderate risk for the development of dangerous rip currents will continue through this evening with the increasing onshore flow. A high risk for the development of dangerous rip currents is expected on Saturday for the DE and NJ beaches, due to a strong onshore northeast flow and waves in the surf zone up to 7 FT. Looking ahead, a persistent onshore flow and elevated seas offshore may lead to a continued high risk of rip currents into Sunday and at least a moderate risk of rip currents into Monday. && .TIDES/COASTAL FLOODING... A persistent onshore northeast flow will continue through at least Sunday. Meanwhile, astronomical tides are decreasing during this time frame, with the afternoon/evening astronomical high tides being the highest. Tides are currently up to 1 ft above the astronomical MLLW at most of our oceanfront, Delaware Bay, and Delaware River gauges. Based on the latest trends and all available guidance, we do not anticipate minor flooding. The only exception along the oceanfront may be the Saturday night high tide if rainfall is substantial enough to add to the storm tide (astronomical + surge) and on the Delaware Bay and River if the northeast flow/rainfall runoff leads to a greater storm tide for the Saturday night and Sunday evening high tides. While these are low probabilities, they will be watched closely. In terms of high surf and beach erosion potential, seas are expected to build in our coastal waters in the 6-8 FT range per WNA guidance. This is typically underdone with northeast gales, so seas may be 1-2 feet higher. With a northeast flow, >=80 pct of these seas will translate onshore in terms of breakers. So there is the potential for 8 FT breakers, which would warrant a High Surf Advisory. Also, seas have trended down every so slightly since the last forecast package. Therefore, we will hold off on a high surf advisory for Saturday with this forecast package. Nevertheless, at least minor beach erosion is likely. && .CLIMATE... Daily rainfall records for today and Saturday at our climate sites are listed below... 7/28 7/29 ACY 2.05 (2012) 2.21 (1884) PHL 8.02 (2013) 3.53 (1980) ILG 2.34 (1914) 1.85 (1913) ABE 3.00 (1969) 1.64 (1979) TTN 2.35 (2012) 2.84 (1961) GED 2.80 (2016) 1.07 (1969) RDG 3.57 (1969) 2.51 (1961) MPO 2.15 (1969) 4.59 (1969) July total ABE: 8.21" is the #8 wettest July on record. The wettest July on record is 10.42" set in 1969. RDG: 8.02" is the #8 wettest July on record. The wettest July on record is 13.85" set in 2004. July average temps: Projecting, for now, PHL 0.9 above normal, losing 1.3 positive departure from the values through the 25th. Ditto approximately the same loss at our other CLI sites will show MPO a little below normal, TTN and ACY near normal, and all other stations above normal. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch through Saturday afternoon for PAZ070-071- 101-102-104. NJ...Flash Flood Watch through Saturday afternoon for NJZ016>027. DE...Flash Flood Watch through Saturday afternoon for DEZ001>004. MD...Flash Flood Watch through Saturday afternoon for MDZ008-012- 015-019-020. MARINE...Small Craft Advisory from 1 AM to 6 AM EDT Saturday for ANZ450>455. Gale Warning from 6 AM Saturday to 2 AM EDT Sunday for ANZ450>455. Small Craft Advisory from 1 AM Saturday to 2 AM EDT Sunday for ANZ430. Small Craft Advisory from 1 AM Saturday to 6 AM EDT Sunday for ANZ431. && $$ Synopsis...Franck Near Term...Iovino Short Term...MPS Long Term...Franck Aviation...Franck/MPS Marine...Franck/MPS Tides/Coastal Flooding...Staff Climate...Staff

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