Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 201942 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 342 PM EDT Wed Sep 20 2017 .SYNOPSIS...
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Tropical Storm Jose will be meandering well offshore through this weekend as it gradually weakens. High pressure centered to our north and west will slowly build closer to our area later this week and into the weekend. A weakening Hurricane Maria should parallel the East Coast offshore during early next week, while a cold front approaches from the west during Wednesday.
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&& .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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The center of Tropical Storm Jose was located about 270 miles east of Atlantic City this afternoon. This system is expected to move slowly to the east-northeast tonight. Our region will remain positioned on the western fringe of Jose`s counterclockwise circulation and to the east of a weak surface ridge along the Appalachians. Visible satellite imagery shows enhanced CU on the western fringe of Jose`s cloud shield over southeastern PA, southern NJ and DE. Weak boundary-layer convergence seems to be promoting the CU development, but with a relatively stable airmass (owing to warm mid levels), convective development should be too shallow to support much more than an isolated shower (or more likely just sprinkles) before sunset. Northerly winds 10-15 mph this afternoon will become light after sunset this evening. Boundary-layer decoupling would be favored in the typical sheltered river valleys of northeastern PA and northwestern NJ, where there is a potential for radiational fog, especially toward early morning. Low temperatures will generally be in the 60s area wide.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
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Large-scale pattern for Thursday very similar to today. Tropical Storm Jose is expected to stall several hundred miles off the NJ coast while high pressure ridges southward down Appalachian spine. Northerly winds should be a few mph lower than today while temperatures are expected to trend upward by a degree or two owing to less cloud cover tomorrow. High temperatures in the mid 80s will be around 10 degrees above normal.
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&& .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
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Summary...A warm pattern through this time frame with a cold front not scheduled to arrive until during Wednesday. Tropical Storm Jose meanders well offshore for awhile, then monitoring Hurricane Maria as it should weaken northward as it parallels the East Coast offshore the first half of next week. Synoptic Overview...A strong ridge is forecast to extend from the Lower Mississippi Valley northeastward to the Great Lakes and toward northern New England through Friday, which then shifts eastward some over the weekend. This ridge should gradually weaken over the weekend into next week as a trough aloft shifts from the western states into the Plains and Midwest. The placement of this ridge and another one near Bermuda will result in very weak steering flow, therefore Tropical Storm Jose is forecast to meander around well east of our coast. Meanwhile, a weakness in the aforementioned ridges as well as the placement of Jose will have an affect on where Hurricane Maria goes as it turns northward. We used a blend of model guidance and continuity for Thursday night through Friday night, then used mostly the 12z WPC Guidance. For Thursday night and Friday...An upper-level ridge is forecast to build some more just to our west and north, which results in strung out surface high pressure. This surface high gradually builds south and eastward, however its progress will be slowed due to Tropical Storm Jose meandering offshore. Jose is forecast to be centered well east of our coast, however its circulation will maintain a northerly wind for our area. Jose currently has a large cloud canopy associated with it therefore as it lingers, at least the eastern parts of our area could see more cloudiness (mainly the high level variety). Despite the ridge aloft not all that far to our and west Friday, some western influence of Jose could keep our temperatures a little cooler. Overall though, most places are expected to get into the 80s Friday afternoon. The western extent of Jose`s moisture should continue to remain well east of our area. For Saturday and Sunday...A rather stuck weather pattern is in place with a ridge that slowly builds a bit to the east. Meanwhile, Jose should still be well east of our coast although it should be spinning down. There could be more clouds at times over the weekend especially closer to the coast given the proximity to the western part of Jose`s circulation. Depending on the steering currents, Jose could make a turn more toward our coast late Sunday. It appears though that any showers will continue to remain east of our region, therefore carried a dry forecast through the weekend. For Monday through Wednesday...This time frame could end up being more challenging as we watch two tropical systems. The first is Jose which is forecast to become post tropical as it spins down off the northern Mid Atlantic coast. Some guidance wants to push its remnants into our area Monday, particularly as the system weakens quite a bit vertically allowing the low-level feature to be steered more westward. We are not certain this will happen at this time as our attention also turns southward to Hurricane Maria. For now, included some slight chance PoPs for much of the area Monday into Tuesday. The track of Maria looks to be partially determined by where Jose goes and if it weakens faster and if Jose is able to help produce a weakness in the ridging (one to the north and west and another near Bermuda). While the consensus overall is to keep Maria offshore of the East Coast, especially as we get into Tuesday and Wednesday, influence from an incoming upper-level trough begins to occur. The timing of this trough will also be important. The presence of Hurricane Maria (which should weaken with a northward extent) looks to be a little close for comfort, therefore monitor the forecasts from the National Hurricane Center and our office for the latest. Pending no showers from dwindling Jose early next week, warm weather should prevail. A cold front does not look to approach until later Wednesday which will also potentially help to keep Maria off the coast. We followed WPC closely and did not go even warmer given more uncertainty with the details especially tied to the tropical activity.
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&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR TAF issued at 18Z with one exception: Vsby may briefly drop to MVFR or lower at RDG just before sunrise Thursday with the expectation that patchy radiational fog forms in the typical fog- prone valleys of NE PA. Do not think other TAF sites should see radiational fog with a light breeze for most of the night. Wind direction will vary between N-W and N-NE through the period. Speeds will be in the 5-12 kt range with gusts 15-20 kt this afternoon, becoming 5 kt or less tonight, then 5-10 kt during the day Thursday. Outlook... Thursday night and Friday...VFR. Northerly winds 10 knots or less during the day, then mostly light and variable at night. Saturday through Monday...VFR overall. Winds favoring between northwest to northeast generally 10 knots or less.
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&& .MARINE...
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Small Craft Advisory continues for our coastal Atlantic waters for the remainder of this afternoon, tonight and Thursday. Winds have steadily decreased throughout the day and are generally in the 10-20 kt range late this afternoon. We may eventually be able to transition to a Small Craft Advisory for Hazardous Seas at some point this evening (especially for southern waters) but decided it was better to hold off at this point with isolated gusts near 25 kt (and to avoid over complicating headlines). Seas, which are currently in the 6-8 ft range at our offshore buoys this afternoon, will continue to subside to 4-6 ft tonight into Thursday. Outlook... Thursday night and Friday...Northerly winds should remain below Small Craft Advisory criteria, however seas will remain elevated as Tropical Storm Jose meanders well offshore. Therefore, the Small Craft Advisory has been extended through the day Friday. Saturday through Monday...A continued northerly wind through this time frame, however it is anticipated to be below advisory criteria. Seas may subside some as Jose weakens, however building swells from Hurricane Maria should arrive with time. Rip Currents... Tropical Storm Jose will continue to push long period (9-12 second) E-NE swells toward the shoreline this afternoon through Thursday. Will continue to carry the high risk for dangerous rip currents for the rest of today. The risk should lower to a moderate risk tomorrow with waves in the surf zone several feet lower than today and with light northerly winds. The risk may drop to moderate for Friday with waves subsiding a bit and winds lighter. However, long period swells from Hurricane Maria should arrive this weekend which could raise the risk to high once again.
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&& .TIDES/COASTAL FLOODING...
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Tidal anomalies remain steady between 1.25 and 1.75 ft above astronomical prediction. Additionally, a new moon tonight has resulted in higher astronomical tides. Will keep the Coastal Flood Advisory for coastal NJ and DE (including the oceanfront, back bays and Delaware Bay) for the next high tide cycle tonight. We also added Talbot, Caroline and Kent Counties along the eastern shore of Maryland to the Coastal Flood Advisory for the impending high tide late this afternoon-early evening. There is a potential for additional minor coastal flooding to persist into the high tide cycles on Thursday but confidence in reaching advisory threshold is low at this point. It looks more like spotty minor tidal flooding as the wind field weakens across the area. We do not anticipate any tidal flooding with today or tonight`s high tide along the Delaware River upstream from the Commodore Barry Bridge area or on the upper eastern shore of Chesapeake Bay.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...High Rip Current Risk until 9 PM EDT this evening for NJZ014- 024>026. Coastal Flood Advisory until 1 AM EDT Thursday for NJZ012>014- 020>027. Coastal Flood Advisory until 2 AM EDT Thursday for NJZ016. DE...High Rip Current Risk until 9 PM EDT this evening for DEZ004. Coastal Flood Advisory until 1 AM EDT Thursday for DEZ002>004. Coastal Flood Advisory until 2 AM EDT Thursday for DEZ001. MD...Coastal Flood Advisory until 9 PM EDT this evening for MDZ015- 019-020. MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ450>455.
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&& $$ Synopsis...Gorse Near Term...Klein Short Term...Klein Long Term...Gorse Aviation...Gorse/Klein Marine...Gorse/Klein Tides/Coastal Flooding...Klein

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