Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 300744 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 344 AM EDT Fri Sep 30 2016 .SYNOPSIS... A frontal boundary will remain stationary to our south today through Saturday with high pressure to our north, and an area of low pressure to our west. The high pressure will begin to break down Saturday night into Sunday. The low to our west will then lift through the Great Lakes region and into the northeast over the weekend, before weakening on Monday. This will pull the frontal boundary across our area Sunday. High pressure builds to our north for Tuesday into Thursday with a northeast flow across the area. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Subtle shift in the flow, primarily in the mid level flow will cause the axis of highest precipitable water to shift north through the day today. As such, many models are depicting a lull in precip for the southern half of our region. However, given how poor models have been handling this event so far, this remains a very low confidence forecast. Even with a lull or light precip in Delmarva, flooding issues could continue as many creeks continue to rise due to the precip over the last 36 hours (see hydrology section). As for temperatures, continue to see little swing in diurnal temperatures due to the precip and persistent cloud cover. Expect highs to generally be within 10 degrees of the low temps this morning. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... The mid level flow shifts a bit more southwesterly overnight, this will decrease the moisture advection somewhat. Additionally, the pressure gradient will continue to relax, meaning low level flow will drop off sharply through the overnight hours. With very limited instability, expect all precip overnight to be stratiform and light. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Unsettled weather continues to be forecast for much of the extended period, especially into the weekend. By Saturday, and especially Sunday, the high to our north begins to move eastward, and the low to our west will begin lifting back toward the Great Lakes region. This will eventually pull the frontal boundary to our south across our area on Sunday. There will continue to be a chance of showers Saturday through Sunday as several short wave/vorticity impulses move across the area as the closed low aloft begins to break down and lift to the northeast. On Monday, the mid-level low will be moving across the area, and the surface low to our north will weaken as it moves into New England. As the mid-level low crosses the area, there could be some scattered showers affecting the area Monday into Monday night. For Tuesday into Thursday, high pressure builds to our north and noses its way across our area. With the high to our north, an onshore flow will develop again, which may end up leading to more cloud cover and cooler conditions. The mid-level trough continues to slowly move across the area Tuesday, which could keep a chance of showers across the area. By Wednesday and Thursday, the trough moves eastard, but with the northeasterly flow and continued moisture, there could be some light rain or drizzle across the area. The focus beyond the extended turns to Hurricane Matthew. The current tracks from the long term guidance is for the system to make the turn to the right and away from the coast before reaching our area. We will need to continue monitoring the forecast over the next several days for adjustments to the forecast track. && .AVIATION /07Z FRIDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Ceilings should generally be hovering between 700 and 1500 ft AGL through much of the TAF period. Some guidance shows a several hours lull in precip through the day. If this comes true, some locations may see temporary improvement to VFR ceilings through the day time hours. However, ceilings are expected to lower once again near or after 00Z. Winds will stay northeasterly through the TAF period. Wind speeds should decrease through the day from SW to NE (KACY will likely be the last TAF site to see gusts drop off). OUTLOOK... Saturday-Saturday night...A prolonged period of MVFR or IFR conditions with periods of rain is expected to affect the TAF sites through the period. East to northeast winds are expected to gust 15-20 knots on Saturday. Sunday-Monday...Some improvement, possibly to VFR. Showers remain possible. Monday night-Tuesday...MVFR or IFR conditions likely to return. Showers remain possible again. East to northeast winds are expected to gust 15-20 knots on Tuesday. && .MARINE... A gale warning continues for all the waters. Winds are expected to slowly decrease from south to north through the day today beginning with the Delaware Bay. Once winds drop below gale conditions, a small craft advisory will likely be needed for the rest of today and tonight due to both wind gusts near 25 kt and lingering high seas. OUTLOOK... Saturday...Winds expected to drop below Small Craft Advisory levels, however, seas may remain above advisory levels through the period. Saturday night-Sunday...Winds and seas expected to drop below Small Craft Advisory levels. Sunday night-Monday night...Conditions expected to remain below Small Craft Advisory levels. Tuesday...Small Craft Advisory conditions may return to the waters. RIP CURRENTS... There is a high risk for the formation of dangerous rip currents along the NJ shore and the DE beaches today. Wave heights should slowly diminish through the day. && .HYDROLOGY... Under normal circumstances, the precip amounts that nearly all guidance is depicting for today and tonight would not be enough to cause flooding issues, and given the lack of instability through the day, expect this event to be transitioning to more of a stratiform event. However, with some locations in Sussex County DE now with over 12 inches of rain over the last 36 hours, even light rain amounts could exacerbate ongoing flooding issues especially in central and southern Delaware. Therefore, have kept the flood watch going through 20Z. As the mid level flow shifts more southwesterly through the overnight hours tonight, moisture advection should decrease, and precipitation should continue to decrease. && .TIDES/COASTAL FLOODING... Minor tidal flooding is expected with the morning high tide cycle for all but the tidal Delaware River. Based on tidal departures we saw with the last high tide cycle, water levels this morning should be solidly in the minor category, but fall short of moderate thresholds (this morning`s high tide is the lower of the astronomical tides). As for the high tide cycle this evening, tidal flooding concerns will depend, to a large part on how quickly the winds drop off through the day today. For now, am forecasting that winds will drop off quickly by mid day (except along the far northern shore) which should lessen the threat for this evening`s high tide. This will need to be revisited through the day. && .CLIMATE... Georgetown broke its daily rainfall record with 6.52 inches. Here are today`s rainfall records. Sept 30 ACY 1.76 1964 PHL 2.41 2010 ILG 4.32 2010 TTN 1.50 1924 GED 3.15 1964 This section below will update on Friday. September will be/is a top 10 warmest month through most of our forecast area, for the 3rd consecutive month! Also September will be/is enjoying a second consecutive top 5 warmest month in the period of record for PHL and ABE. We`ve run the actual numbers through the 28th, then added the forecast high/low for 29th and 30th. Philadelphia: Expect a 73.8 degree average or about 5 degrees above the monthly normal of 69.1. This will be a #4 or #5 warmest September on record for Philadelphia. Philadelphia September average temperature rankings 75.4 -1881 74.5 -2015 74.1 -1931 74.1 -1930 73.8 -2005 and 2016 #4 (small chance PHL avg will be 73.7 or #5 ranking) 72.9 -2010 72.9 - 1921 Philly ranked #7 warmest July followed by a warmest ever August in the POR dating back to 1874. Atlantic City: Expect a 71.2 degree monthly average temperature, or 4 degrees above the monthly normal of 67.2. This would equate to an 8th warmest September in the period of record dating back to 1874. Atlantic City recorded a #7 warmest July and then a warmest ever August. 73.3 - 1961 72.8 - 1881 72.3 - 1931 and 1930 71.7 - 1921 71.6 - 2015 71.5 - 1933 71.3 - 2005 71.2 - 2016 #8 71.0 - 2010 70.6 - 2011 and 1906 Allentown: Expect a monthly average of 69.4 degrees, or 5.5 degrees above the monthly normal of 63.9 and a 4th warmest September on record. Allentown ranked 8th warmest July and #2 warmest August in the period of record. 70.8 - 1961 70.3 - 1980 69.7 - 2015 69.4 - 1931 and 2016 (small chance Allentown will rank #5 at 69.3 degrees) 68.7 - 2005 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Flash Flood Watch through this afternoon for PAZ070-071. NJ...High Rip Current Risk through this afternoon for NJZ014- 024>026. Flash Flood Watch through this afternoon for NJZ016>027. Coastal Flood Advisory from 7 AM this morning to noon EDT today for NJZ012>014-020>027. Wind Advisory until 6 AM EDT early this morning for NJZ020- 022>027. Coastal Flood Advisory from 10 AM this morning to 1 PM EDT this afternoon for NJZ016. Wind Advisory until noon EDT today for NJZ013-014. DE...High Rip Current Risk through this afternoon for DEZ004. Flash Flood Watch through this afternoon for DEZ001>004. Coastal Flood Advisory from 7 AM this morning to noon EDT today for DEZ002>004. Wind Advisory until 6 AM EDT early this morning for DEZ003-004. Coastal Flood Advisory from 10 AM this morning to 1 PM EDT this afternoon for DEZ001. MD...Flash Flood Watch through this afternoon for MDZ008-012-015- 019-020. MARINE...Gale Warning until noon EDT today for ANZ452-453. Gale Warning until 2 AM EDT Saturday for ANZ450-451. Gale Warning until 8 AM EDT this morning for ANZ454-455. Gale Warning until 6 AM EDT early this morning for ANZ430-431. && $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson Hydrology...Johnson Tides/Coastal Flooding...Johnson Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.