Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 162021 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 421 PM EDT Sat Sep 16 2017 .SYNOPSIS...
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High pressure gradually builds to our north and east into Monday. All interests in coastal areas of New Jersey and Delaware should follow the forecast of Hurricane Jose as it moves northward off the mid-Atlantic coast, probably passing well east of New Jersey Tuesday into Wednesday. High pressure is expected to settle back down into our area late in the week, behind the departing Jose.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... A weakening trough aloft will continue to be over our area through tonight. There remains a fairly large area of strung out short wave energy associated with it. A mesoscale analysis this afternoon indicates surface-based CAPE ranging from 500-1200 j/kg across the region, with the highest focused across northern New Jersey and portions of eastern Pennsylvania. The flow is on the light side and despite disorganized lift, some showers will continue through late this afternoon. The shower development has been mostly focused to terrain, then the activity is sliding southwestward due to a weak northeasterly flow. This activity is tied to daytime heating, therefore we are expecting them to dissipate very early this evening. As we go through tonight, there are some mixed signals regarding the development of stratus and fog. The setup looks to be conducive for both given the light flow and no real change in the airmass. As the boundary layer cools, saturation is expected for many areas and this would point to fog development assuming no clouds above. There was some stratus along parts of our coast this morning, and this has since dissipated although there is some lurking just south of Long Island this afternoon. Given the light onshore flow, this area of low clouds should advect west and southwest some through the night. Some guidance is not all that robust with this, perhaps due to the weak flow, but shows some fog, while other guidance indicates stratus gets to at least the coastal areas. Since the flow is not all that strong, we favored stratus development for the coastal areas especially. Farther inland however may end up having more fog especially if there are no clouds aloft. Given the mixed signals, we carried a fog mention however did not include dense fog. Low temperatures are mostly a MOS/continuity blend. The hourly temperature, dew point and wind grids were initially adjusted based on the latest observations, then the LAMP and some high-res guidance was blended in through the evening. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... A similar setup for Sunday as some ridging occurs across the Northeast, although a weakness still exists as a trough aloft remains across our region. Given the lighter flow, stratus and/or fog will dissipate during the morning although this may be slower along the coastal areas (assuming it is in place to start). Once any fog and/or stratus dissipates, we should have a similar day compared to Saturday with cumulus development occurring by late morning. Given the onshore flow, this may leave the coastal locales with more sunshine compared to inland during the afternoon (assuming any stratus/fog dissipates). Once again some showers cannot be ruled mainly in eastern Pennsylvania to northern New Jersey where terrain should assist in some development. We are not expecting much coverage given a lack of overall forcing and flow, and again should be low-topped and therefore left out a thunder mention. We continued with some low mentionable PoPs during the afternoon. High temperatures are mainly a blend of MOS and continuity. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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The main story remains Hurricane Jose and its pass off our coast next week. All of that follows shortly. Temperatures: Calendar day averages this 6 day period should be close to 9 degrees above normal the rest of this week and continue warmer than normal for possibly another week beyond that. The monthly negative departure should be virtually erased by next weekend and at that time monthly averages should be warming above normal. Forecast basis: 50 50 blend 12z/16 GFS/NAM MOS Sunday night-Mon night. Then the 12z/16 MEX MOS guidance was used for Tuesday with TCM wind tool "checked" but not used as an overlay on the sustained wind since TCM34 kt winds were a few NM east of our waters. Thereafter, the 15z D4-8 WPC grids for Wed-Sat. The dailies... Sunday night...nearly calm with any daytime showers probably dying out at sunset. Stratus and fog may become widespread late at night. Monday through Wednesday...Please see the forecast discussion from the National Hurricane Center for the latest details on the forecast track of Hurricane Jose. For our area, we are still looking at a track with the center passing 200-250 miles off shore, though still close enough for impacts to our region. At this point, we are expecting most of the impacts on Tuesday. This portion of the AFD indicates forecast anticipations. We will note where expectations are solidly categorical and where there is greater uncertainty. Sundays AFD`s and products will probably have some hazard issuances but we`re meshing the anticipations of our national centers and the WFO`s in a manner that will have coherent messaging. We should know considerably more at this time tomorrow about impacts from Jose and if they will be significant. Storm track looks pretty well clustered but western fringe of the 34 knot and 50 knot sustained wind envelope will ultimately determine the NJ and DE impacts. Confidences in those winds are expressed through the NHC wind probabilities. What is likely from this system in our waters and adjacent nearby shores. 1) HIGH SURF (10-15 foot seas) and HIGH risk dangerous rip currents...mainly Monday night Tuesday night. Confidence: above average. 2) Tidal flooding. A 1 to 2 foot storm surge at the times of high tides Monday evening through Tuesday evening. Confidence on a 1 foot surge is above average. Confidence on a 2 foot or slightly higher storm surge for Tuesdays Atlantic coast high tide cycles and possible moderate coastal flooding is, below average. So minor coastal flooding likely but anything more than that is below average confidence. Greater uncertainty below.. 3) Tropical sustained 34 knot wind gusts. Possible, mainly in the coastal waters. Confidence as expressed by the NHC 34 knot wind probabilities...is a little less than average. However, it will be close and 34 knot gusts are probable but the somewhat stronger sustained wind of 34 kt is less confidently assessed and stated. Nevertheless we expect a breezy Tuesday and possibly Wednesday over our area with gusts at least 25-30 mph. 4) Heavy Rain: Current track keeps the heavy rain off shore on Tuesday, with our area only seeing the outer rain bands. However, any additional rain at the shore near or shortly before a high tide could exacerbate coastal flooding. Finally, Thursday-Friday-Saturday...Most of the operational models depict a high amplitude ridge beginning to build over the region through this period, but it remains uncertain how quickly this will build. In addition, if it develops far enough north, we could be in a on shore low level flow regime for our area, tempering any warming trend due to the increasing thicknesses.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This afternoon...VFR with cloud bases in the 3,500-5,000 feet range. Isolated to scattered showers will be around. Winds light and variable, or locally light from the southeast. Tonight...Any showers end early, then some fog and/or stratus should develop initially in the KACY and KMIV areas. There is less certainty how far inland the stratus gets as it may be more fog. If less stratus develops, then fog may end up becoming more widespread with significant visibility restrictions. Winds light and variable to locally calm. Sunday...Fog and/or stratus dissipates in the morning, then VFR. A few inland afternoon showers cannot be ruled out mainly north and west of KPHL. East to northeast winds less than 10 knots, possibly turning locally southeast in the afternoon. Outlook... Sunday night...VFR to start, then IFR stratus-fog should develop late at night in light northeast surface wind...especially e PA and nw NJ. Monday...IFR cond improve as cigs lift to VFR sct-bkn aoa 3500 ft during the afternoon except possibly MVFR cigs during the aftn along the coast. Gusty northeast wind ~ 15 kt. Monday night-Tuesday...Expect conditions to deteriorate to MVFR or lower along the coast with VFR cigs elsewhere. Gusty northeast winds much of the region, with KACY having the highest risk of gusts above 30 KT. Wednesday...Becoming VFR with decreasing north to northwest winds... gusting 15-20 kt. Thursday...VFR. Light north wind.
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&& .MARINE...
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The winds are expected to be well below Small Craft Advisory criteria through Sunday. However, swells are expected to gradually build through Sunday due to distant Hurricane Jose. This should get seas into the 5-6 foot range through Sunday and therefore the Small Craft Advisory for Hazardous Seas goes into effect early this evening for the ocean zones. Some locally dense fog is possible later tonight and early Sunday morning, mainly nearshore. Outlook... Sunday night...SCA seas for the Atlantic waters. Monday through Wednesday...Tropical storm conditions will be possible Tuesday. However, even Monday, winds may be above SCA criteria (~25 kt) in advance of Hurricane Jose approaching from the south. Although winds will begin to diminish Wednesday, it will take time for seas to subside. A tropical storm or gale related marine hazard may issue sometime tomorrow...all dependent on internal assessment of the wind fields. Rip Currents... Monday-Tuesday...HIGH risk for the formation of dangerous rip currents. Wednesday...Still a residual moderate risk.
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&& .TIDES/COASTAL FLOODING... Coastal flooding is possible with the high tide cycles Monday through Tuesday night due to the passage of Hurricane Jose. A prolonged period of east to northeast winds will allow water to pile up along the shores. In addition, there is a new moon on Wednesday, September 20, so astronomical tide levels will be running high. Depending on how close Jose tracks to the coast changes how significant the coastal flooding will be. As of now, minor coastal flooding is likely with the high tide cycles from Monday afternoon through Tuesday night. If Jose tracks closer to the coast, then widespread moderate coastal flooding will become more likely. If the timing of Jose slows down, then high tide cycles on Wednesday may be affected as well. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Monday for ANZ450>455.
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&& $$ Synopsis...Drag 420 Near Term...Gorse 420 Short Term...Gorse Long Term...Drag Aviation...Drag/Gorse 420 Marine...Drag/Gorse 420 Tides/Coastal Flooding...420

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