Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 160744 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 344 AM EDT Sat Sep 16 2017 .SYNOPSIS...
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Weak high pressure will build over our region through the weekend. Hurricane Jose is forecast to move northward off the mid-Atlantic coast through mid week, passing near our region Tuesday into Wednesday. High pressure is expected to once again build over our region late in the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Areas of fog have developed across portions of the area. The most widespread and thickest is across portions of southern New Jersey, as well as portions of central/southern Delaware and portions of eastern Maryland. Some of this fog will be locally dense at times. Elsewhere, patchy fog could also develop through sunrise, especially river valleys and rural spots. This fog will all dissipate quickly after sunrise. Once the fog burns off, we expect cloud cover to increase through the morning and especially into the afternoon as moisture pools at the top of the mixing layer. Our area will remain under the influence of a weak trough/low aloft and its associated vorticity, as well as a rather diffuse surface trough. These features will help lead to some enhanced lift across the area today, which in turn could help create some scattered showers, especially across eastern Pennsylvania and northern New Jersey. There is some weak instability across the area, so an isolated thunderstorm may be possible.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
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The showers that develop during the day are expected to dissipate around or after sunset as daytime instability wanes. Once the sun goes down and the surface temperatures cool, areas of fog and/or stratus should begin to develop across the area. How thick the fog becomes is still uncertain at this time, but areas that receive rainfall today have the greatest threat for the fog to develop.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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The main story remains Hurricane Jose and its pass off our coast next week. First on Sunday, we could once again see some isolated to scattered shower coverage in the afternoon under a weak mid and upper level low. Temperatures should be similar to what we have seen the last several days with highs ranging from the lower 70s to lower 80s. 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 several miles off shore, though still close enough for impacts to our region. At this point, we are expecting most of the impacts on Tuesday, though it should be noted there are still large timing differences between the models. As for the impacts for our region: Wind: With the latest track, it appears unlikely, though not impossible, that our land areas will see winds of tropical storm force. That being said, Tuesday into Wednesday will be quite breezy at the shore. Coastal Flooding: Please see the section below on the potential for coastal flooding Monday into Tuesday night. 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. Rip currents: Please see the discussion under the marine section for details on the rip current risk. Thursday and Friday...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 /07Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Areas of fog have developed across southern New Jersey, as well as portions of central/southern Delaware and portions of eastern Maryland. Locally dense fog has developed in these areas, and ACY and MIV are experiencing VLIFR conditions. Elsewhere, patchy fog is expected to develop through sunrise, but likely will not be as dense and range from IFR to MVFR. The fog is expected to dissipate around or shortly after sunrise. Cloud cover is expected to increase through the morning and and into the afternoon. Bases are forecast to be around 3,500-4,500 feet today, but could reach as low as 2,500-3,000 for a period at ABE and RDG. There is a chance of scattered showers to develop this afternoon, before dissipating by this evening, so a PROB30 was included for the shower potential. There is an even smaller chance of thunderstorms, but these were not included in the TAFS. Once any showers dissipate, the next concern for tonight becomes the potential for fog/stratus to develop overnight. How thick the fog becomes is still uncertain at this time, but areas that receive rainfall today have the greatest threat for the fog to develop. Outlook... Sunday...Once the fog dissipates, should have VFR conditions through the day. Another round of fog with visibilities of MVFR or lower is possible Sunday night, but details are uncertain at this time. Monday-Tuesday...Expect conditions to deteriorate to MVFR or lower across most of the region especially Monday night into Tuesday as Jose passes near our coast. KABE and KRDG may stay VFR for much of the period as they may be west of the main rain shield. Breezy easterly winds are possible for much of the region, with KACY having the highest risk of gusts above 30 KT. Wednesday...Becoming VFR with decreasing northwest winds.
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&& .MARINE...
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Seas are forecast to be 3-4 feet on the waters today, so sub Small Craft Advisory conditions are expected during the daytime. However, seas are expected to build to 5-6 feet by this evening and remain through the overnight hours. Winds are expected to remain 5-10 knots through today and tonight. We will need to keep an eye on the fog that has developed from northern Long Island, NY northward through New England to see if it starts to spread down into our area. Outlook... Sunday...SCA conditions are expected primarily for seas above 5 feet and primarily for the coastal waters and lower Delaware Bay. Monday through Wednesday...Tropical storm conditions will be possible Tuesday. However, even by Monday morning, winds will be above SCA criteria in advance of Hurricane Jose approaching from the south. Although winds will begin to diminish Wednesday, it will take time for seas to subside. Rip Currents... With a 3-4 swells of 12-13 seconds forecast for today, along with a developing easterly wind of 5-10 knots, we expect a moderate risk for the development of dangerous rip currents. A moderate or even high risk is expected to continue through at least mid week as we continue to see the swells from Hurricane Jose reach our shores.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas from 6 PM this evening to 6 PM EDT Sunday for ANZ450>455.
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&& $$ Synopsis...Johnson Near Term...Robertson Short Term...Robertson Long Term...Johnson Aviation...Johnson/Robertson Marine...Johnson/Robertson Tides/Coastal Flooding...

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