Area Forecast Discussion
Issued by NWS Upton, NY

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571 FXUS61 KOKX 211012 AFDOKX Area Forecast Discussion National Weather Service New York NY 512 AM EST Sat Jan 21 2017 .SYNOPSIS...
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Weak high pressure departs later today. Deepening low pressure approaches from the southwest Sunday and will reach the southern Mid Atlantic region by Monday morning, while high pressure builds southeast into the Canadian Maritimes. The low will intensify into a significant coastal storm as it moves up the coast toward the area Monday through Tuesday. High pressure builds for Wednesday as the coastal low departs towards New England. A cold front slowly approaches the area from the west, moving through late Thursday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Upper ridge builds, with subsidence noted behind weak shortwave energy that produced light rain earlier. Plenty of low level moisture trapped underneath inversion through the day today. Weak sun may not be enough to scour out any of these low level clouds. Some breaks in the clouds are possible, but generally expect a mostly cloudy day today. As such, any clouds and patchy fog early could give way to some sunshine, but generally expect the clouds to predominate. Temperatures will greatly depend on amount of sunshine that is realized. Expect high`s in the 50s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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Through this time frame, ridge axis moves east, as upstream energy traverses across the mid west and approaches the area Sunday. Warm air advection commences tonight, with a warm frontal boundary, extending eastward from mid west low, remaining to the south of the area through this timeframe. As the strengthening trough approaches, the low deepens as it tracks across the Appalachians. With a strong high building toward the Canadian Maritimes, a tightening pressure gradient is noted by late Sunday. Plenty of low level moisture remains in place with light flow tonight. Low clouds and patchy fog are anticipated tonight. Rain chances increase from the south Sunday as warm front draws near. Lows tonight range from the 30s well inland to the mid 40s in and around NYC. On Sunday, temperatures rise into the 50s, although increasing easterly flow prevents much more of a rise as the day progresses.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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Significant coastal storm likely Sunday Night into Tuesday with potential high wind...heavy rain...and coastal impacts. Have issued a High Wind Watch for Long Island, coastal CT, New York City, and some adjacent parts of urban northeast New Jersey from late Sunday night into much of Monday night. The watch covers the time frame when wind gusts in those areas will likely exceed 40 mph, with the highest winds capable of meeting high wind criteria occurring mainly from late morning into the evening. Siding with slower/stronger 00Z NAM/03Z SREF as the precursor synoptic pattern is somewhat blocky, the storm very well could slow down as it closes off and becomes negatively tilted aloft. Think sustained east winds in the warning area will reach 30-40 mph with gusts 60-65 mph, with the strongest winds across Long Island and parts of NYC closest to the ocean. Farther north/west, wind gusts will likely approach or exceed wind advisory criteria, reaching 40-50 mph, with the highest speeds closer to the coast and in the higher elevations. ECMWF ensemble wind probabilities continue to support this general idea as well, with 80-90% probability of 50+ kt wind gusts over the ocean waters, and 50% probability just inland. Slow moving coastal storm passes just south by Tuesday per model consensus, with a 1 to 3 inch rainfall likely. The heaviest rain occurs Monday as trough becomes negatively tilted, and abundant moisture gets pulled northward ahead of the slowing system. Plenty of Atlantic moisture advects northward ahead of this low, with the warmer air riding over the cooler air entrenched over the northeast. Diabatical cooling is expected, but perhaps not enough for much wintry weather across the interior. Gradually improving conditions occur later Tue into Tue Night as the upper low pivots northeast and low pressure tracks up the New England coast.
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&& .AVIATION /10Z SATURDAY THROUGH WEDNESDAY/... Weak high pressure returns today. MVFR conditions prevail early this morning, with IFR conditions locally observed. Localized LIFR is possible early. Winds remain light mainly out of the south or southwest. These winds remain southwest to west, under 10 kts during the daytime. Due to the latest forecast guidance showing more of an inversion profile in the low levels have decided to go MVFR with at least broken cloud coverage for most of the day. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 .OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY... .Late tonight...MVFR conditions will give way to IFR, with possible LIFR conditions. Possible fog for some locations. .Sunday-Sunday Night...MVFR or lower in light rain, then moderate rain at night. NE winds G20-30KT by late day, and G30-40KT later at night. LLWS possible late Sunday night. .Monday-Monday Night...IFR conditions with LLWS. Moderate to heavy rain is expected at all terminals, except perhaps KSWF where some snow may mix with the rain, but guidance is trending warmer now. ENE winds 25-30KT with G40-45KT. .Tuesday-Tuesday night...Rain tapering off by the afternoon and with improving ceilings into the evening. NW winds G25-35KT, highest in the morning. .Wednesday...VFR. && .MARINE...
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Quiet through Sunday afternoon, then winds should quickly ramp up to SCA Sunday evening and to gale force later Sunday night. Storm Watch remains in effect for late Sunday night into Monday night. Easterly wind gusts 50-60 kt expected mainly daytime Mon into Mon evening on the ocean, and beginning a little bit later Mon morning on the remaining waters. Strongest winds will be on the ocean, and even higher gusts 65-70 kt are not out of the question per 00Z NAM, which predicts 950-975 mb winds that strong and either a well-mixed or moist absolutely unstable layer (MAUL) to enable these winds to reach the surface. If forecast trends continue to increase a hurricane force wind watch might be needed for a portion of the ocean waters. Max seas could peak at 20-22 ft on the ocean, 9-12 ft from Orient Point east, and 8-9 ft on central Long Island Sound, per combo of WaveWatch/NWPS guidance and wind/wave climatology.
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&& .HYDROLOGY...
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Likelihood of 1 to 3 inches, with locally higher amounts possible with a coastal storm Sun night into Monday...with heaviest rainfall Mon aft/eve. If high end rainfall amounts are realized...this will bring a threat for moderate urban flooding and minor small stream flooding in NE NJ/Lower Hud Valley. This would be exacerbated by coincidence of high tide with the heavy rain Mon eve. Rises on larger rivers would be likely...but at this point the potential for minor flooding appears slight.
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&& .TIDES/COASTAL FLOODING... A strong coastal storm will likely cause 3 successive high tide cycles of minor coastal flooding Sunday Night into Monday Night...with potential for locally moderate coastal flooding with the Monday evening high tide. This moderate threat could linger into the early Tue morning high tide cycle. An ensemble of guidances is showing potential for surge building to 3 1/2 to 4 1/2 ft by Monday evening. The highest threat for coastal impacts will be for flood prone locales along the south shore bays of Li/NYC...eastern bays of LI...lower NY/NJ harbor including tidally affected rivers...and western Li Sound. The other concern will be for widespread dune erosion and localized washovers at Atlantic ocean beaches from long period easterly swells of 15-20+ ft Mon into Tue. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...High Wind Watch from late Sunday night through late Monday night for CTZ009>012. NY...High Wind Watch from late Sunday night through late Monday night for NYZ071>075-078>081-176>179. NJ...High Wind Watch from late Sunday night through late Monday night for NJZ006-106-108. MARINE...Storm Watch from late Sunday night through late Monday night for ANZ330-335-338-340-345-350-353-355.
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&& $$ SYNOPSIS...Goodman/PW NEAR TERM...Goodman/PW SHORT TERM...Goodman/PW LONG TERM...Goodman/PW AVIATION...PW MARINE...Goodman HYDROLOGY...Goodman/PW TIDES/COASTAL FLOODING...

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