Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 171856 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 256 PM EDT Sun Sep 17 2017 .SYNOPSIS... High pressure from New England to the Maritimes dominates our weather into Monday. All interests in coastal areas of New Jersey and Delaware should continue 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 weakening remains of Jose. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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A very similar pattern through tonight as a weakness aloft remains across the region with an area of strung out short wave energy. This combined with not much in the way of mixing has led to the slower erosion of the earlier low clouds. These have since morphed into more of a convective looking cloud pattern now, with even a few showers popping up. The shower development should be most focused on differential heating boundaries of earlier along with terrain influences and local areas of low-level convergence. Given the slower erosion of the lower clouds, instability has been slower to increase and therefore the shower coverage may end up being even less than what was observed yesterday. The precipitable water values are still above an inch, therefore any stronger and slow moving shower will be capable of producing localized heavy rain. Once any showers dissipate early this evening, we then turn to the development of stratus and fog once again. We are favoring more stratus instead of widespread fog overnight especially from about the I-95 corridor on eastward. This is due to the onshore flow continuing along with plenty of lower clouds offshore this afternoon. As the boundary layer cools through the evening, the low clouds should expand/redevelop westward. Going with the idea of more stratus, did not hit the fog real hard at this point however did continue to include at least patchy fog across the region overnight. The NAM and even some of the high-res guidance hinting at some possible showers or drizzle toward daybreak across portions of the coastal plain. This may be associated with an initial narrow area of convergence well ahead of Hurricane Jose. We therefore included some slight chance PoPs for now as coverage is less certain. Low temperatures are a blend of mostly MOS and continuity, and the hourly temperature grids are a blend of MOS and some high-res guidance. The grids for the rest of this afternoon are being adjusted based on observations and radar/satellite trends.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
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As we start the day Monday, ongoing stratus and some fog is expected to improve through the day. This may take the entire morning and even into the early afternoon for most places (especially the stratus), however we do think there should be some improvement for a time. As we look to the synoptic scale, some resemblance of the weak trough aloft remains on Monday. All the focus turns to Hurricane Jose moving northward as it parallels the East Coast. The tropical system is not anticipated to really have an influence on our weather during the day Monday, although some increase in the northeasterly wind is expected in the afternoon mainly closer to the coast. There may still be a zone of weak convergence within some instability to pop a few showers once again Monday afternoon. This looks to be near and north/west of the I-95 corridor especially with any ongoing morning showers pivoting to the west. We therefore continued with some slight chance PoPs with the idea of isolated showers. As the onshore flow starts to increase especially later in the day, temperatures should be a bit cooler. The high temperatures will also be dependent on how quickly the stratus breaks. High temperatures are mainly a MOS/continuity blend.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... What is stated here in the long term sections that follow is preliminary. As has been the case the last several days, the focus in the long term is on Hurricane Jose and the size of its 34 knot sustained wind field, as the center of Hurricane Jose probably passes 200 to 250 miles east of NJ later Tuesday or early Wednesday. Please see the forecast discussion from the National Hurricane Center for the latest details on the forecast. Note that with the 11 am advisory the probabilities for sustained 34 knot (tropical) winds has increased considerably. Those probabilities will be incorporated into the forecast wording at the 1230 PM issuance. 1. High Surf resulting in beach erosion and a high risk of rip currents: Though guidance has been running a foot or two on the high side since late yesterday, we expect reality to catch up to the guidance, though possibly not until late Monday. Highest wave heights will probably occur Tuesday...of at least 10 feet, possibly 16 feet in the Atlantic coastal waters. We have high confidence of at least 10 feet. 2. Tidal flooding: We have very high confidence that tidal coastal flooding will occur, though there is still some uncertainty with the severity of the coastal flooding. See the coastal flooding section below for more details. 3. Tropical Storm force winds (sustained of 34 KT or higher): Recent guidance trends suggest the potential continues for a period of sustained 34 kt winds along the immediate coasts Tuesday and Tuesday night but no TSa at this time for the land. There is a better chance for sustained 34 knot winds on portions of our Atlantic Coastal waters and a tropical storm watch may be issued for the marine zones late this afternoon, pending receipt of and in-house WFO-NHC collaborating multiple model guidance. For now...gusts 30-40 MPH in parts of NJ and DE are possible Tuesday, stronger gusts of 40 kt possible on the Atlantic waters but still plenty...of uncertainty. 4. Heavy Rain: Current track keeps the heavy rain just off shore on Tuesday, but WPC does have us with a marginal 2-5% chance of excessive rain from Ocean and Monmouth counties northeastward. Any excessive rain at the shore near or shortly before a high tide could exacerbate coastal flooding, especially Tuesday evening north of Atlantic City. Post Jose--- Thursday through Saturday...A high amplitude ridge should begin to build over our region. The pressure pattern may not allow a quick demise and departure of Jose so that a northeast gradient of moist marine air may tend to linger. This would temper the potential of the warming trend due to the building high to our north and some marine influence. As far as the week as a whole goes for temperatures: Daily calendar day averages for the week should average close to 10 degrees above normal...possibly only 7 degrees above normal next weekend. Still there is no end in sight for the persistent late summer warmth with above normal temps expected to continue through week two (the end of September). && .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This afternoon...Lingering MVFR ceilings improve to VFR. Mainly isolated shower coverage inland from the coast. Winds favoring a northeast to east direction of 10 knots or less. Tonight...Any showers end early, then areas of stratus and fog redevelop overnight resulting in IFR conditions. The arrival time of the MVFR to especially IFR conditions is of lower confidence. Light and variable winds overall. Monday...IFR conditions due to low clouds and/or fog, then improving to MVFR/VFR after 15z. Northeast winds increasing to around 10 knots with the highest mainly at KACY in the afternoon. Outlook... Monday night...Widespread MVFR cigs likely. northeast wind, increasingly gusty PHL to ACY, MIV and ILG during the night...near 20 kt late. A good chance of showers developing vcnty KACY. Tuesday...VFR conditions are expected to develop at KRDG and KABE. For the Delaware Valley TAF sites (KPHL, KILG, KPNE, and KTTN) and coastal sites (KMIV and KACY) MVFR ceilings are likely....possibly lower with showers likely vcnty KACY. Northeasterly winds 10 to 20 KT with gusts to possibly past 30 KT except gusts only 20-25 kt vcnty KABE/KRDG. Wednesday...Becoming VFR with decreasing northwest winds...gusting 15 to 20 KT. Thursday...Mostly VFR conditions are expected. Light winds shifting from northerly to northeasterly.
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&& .MARINE...
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The swell energy from Hurricane Jose will continue to arrive through Monday. The winds are on the lighter side, however it will increase during the day Monday from a northeasterly direction. It is possible that wind gusts near 25 knots across the southern ocean zones toward later Monday afternoon. Therefore, not planning to extend the Small Craft Advisory for Hazardous Seas especially given the eventual approach of offshore Hurricane Jose. The seas/swells have been slower to build across our waters, therefore slowed this down a bit more through tonight as we await the increase in winds. The conditions will remain below advisory criteria on Delaware Bay. Outlook... A tropical storm marine hazard may be issued at 5 PM...dependent on internal assessment of the wind fields. Monday night through Wednesday...Tropical storm conditions will be possible Tuesday. Although winds will begin to diminish Wednesday, it will take time for seas to subside. Wednesday night and Thursday...once seas subside below 5 ft Wednesday night, winds and seas should stay below SCA criteria for the remainder of the period. Rip Currents... Swells of 4-5 feet (11-14 second period) combined with an onshore wind is resulting in dangerous rip currents. Therefore, we continue the high risk through tonight. As the swell energy builds on Monday and the winds gradually increase from south to north, the rip current risk is expected to remain at high. The high risk will continue through mid week. Despite comfortable water temps in the lower to mid 70s swimming at the beaches is not recommended the next few days due to rough and gradual increasing and dangerous surf. ANKLE DEEP only. Please follow the advice of local officials.
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&& .TIDES/COASTAL FLOODING...
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Widespread minor to possibly moderate tidal inundation coastal flooding is expected with the Atlantic coast high tide cycles Monday evening through Tuesday night due to the passage of Hurricane Jose. Whether it is moderate is debatable but we have several model guidances suggesting 2 to possibly 3 consecutive high tide cycles of moderate coastal flooding are possible. The high tide cycle of greatest concern at this point is the Tuesday evening high tide, especially Sandy Hook to Cape May. We may be issuing a coastal flood watch of some sort at 5 PM. So we dont know for sure if we see areas of moderate coastal flooding but the potential for exceeding the moderate threshold exists. A prolonged period of east to northeast winds will force water to build along the shores. In addition, there is a new moon on Wednesday, September 20th, so astronomical tide levels will be running high. Positive departures along the Atlantic coast compared to the astronomical prediction yesterday (24 hours ago) were about .4 feet higher, today the departure has increased slightly to about .6 FT. All of this with very little easterly inflow and relatively high surface pressure.
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&& .EQUIPMENT... KSMQ transmission of data continues ots. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...High Rip Current Risk until 11 PM EDT this evening for NJZ014- 024>026. DE...High Rip Current Risk until 11 PM EDT this evening for DEZ004. MD...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EDT Monday for ANZ450>455. && $$ Synopsis...Drag Near Term...Gorse Short Term...Gorse Long Term...Drag/Johnson Aviation...Drag/Gorse Marine...Drag/Gorse Tides/Coastal Flooding... Equipment...

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