Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 171628 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1228 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 PM THIS EVENING/...
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The areas of stratus are finally thinning and lifting as heating continues. The visible satellite imagery shows the cloud pattern now becoming more convective looking. The extensive cloud cover though has slowed the temperature increase for much of the area thus far, therefore adjustments were needed. In addition, the high temperatures were lowered a little for much of the area. Not much difference in the synoptic setup compared to yesterday, with a weak trough aloft sitting across the region. While the forcing is weak, local convergence combined with enough instability this afternoon will allow for isolated to perhaps scattered showers once again. These should be primarily inland from the coast, although the start of this is delayed some due to the slow erosion of the stratus. The 12z Sterling, VA raob indicates a strong inversion once again near 700 mb, while the 12z Upton, NY raob has less of an inversion. Some of the high- res guidance hinting at the most shower development near the I-95 corridor, although the main focus may be near remaining differential heating boundaries. Overall, we are anticipating low-topped activity therefore will continue with no thunder mention. Despite this, precipitable water values from the two nearby raobs are 1.2 to 1.4 inches, therefore any slower moving shower that is able to develop will be capable of producing localized heavy rainfall. The hourly temperature, dew point and wind grids were adjusted based on the latest observations, then the LAMP guidance was blended in for a few hours. The cloud cover was adjusted upward for awhile longer given trends.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... The showers that develop during the day are expected to dissipate around or after sunset as daytime heating wanes. Once the sun goes down and the surface temperatures cool, areas of fog and/or stratus should begin to develop and spread across the area from east to west. Overall fog is not expected to be widespread dense, but a some locally patchy dense fog will be possible. && .LONG TERM /MONDAY 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 /18Z 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...MVFR ceilings are expected to improve to VFR ceilings. Isolated to scattered showers are expected later this afternoon, especially inland from the coast. Light and variable winds, favoring a northeast to east direction of 10 knots or less. Tonight...Any showers end early, then areas of stratus and fog are expected to redevelop especially overnight. This will result in areas of IFR or lower conditions. Light and variable winds overall. Monday...MVFR/IFR or lower conditions due to low clouds and fog, then improving to VFR after 14z. Northeast winds 10 knots or less, however increasing to 10-15 knots in the afternoon at KACY. 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 seas are running about a foot lower than forecast, therefore delayed the increase some through the afternoon. Overall, seas on the ocean build to 4-6 feet toward the end of the day then remain tonight. We will continue with the Small Craft Advisory for Hazardous Seas. The conditions will remain below advisory criteria on Delaware Bay. An onshore flow is expected through tonight with winds mainly at and below 15 knots. Outlook... A tropical storm marine hazard may be issued at 5 PM...dependent on internal assessment of the wind fields. Monday through Wednesday...Tropical storm conditions will be possible Tuesday. However, even Monday, northeast wind gusts may increase above 25 KT late in the day and at night in advance of Hurricane Jose approaching from the south. 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... With swells of 12-13 seconds forecast to build to 5-6 feet later today, along with an easterly wind of 5-10 knots, we will continue with a high risk for the development of dangerous rip currents today. 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... 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. && .EQUIPMENT... KSMQ transmission of data continues ots. && .PHI WATCHES/WARNINGS/ADVISORIES...
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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.
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&& $$ Synopsis...Drag Near Term...Gorse Short Term...Robertson Long Term...Drag/Johnson Aviation...Drag/Gorse Marine...Drag/Gorse/Robertson Tides/Coastal Flooding... Equipment...

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