Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 150841 AFDOKX Area Forecast Discussion National Weather Service New York NY 441 AM EDT Tue Aug 15 2017 .SYNOPSIS...
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A warm front south Long Island will slowly move northward today, while a weak cold front approaches from the northwest. This weak front will move across tonight, followed by high pressure building from the northwest on Wednesday. The high will move offshore Wednesday night and Thursday, followed by a warm front moving north Thursday night into Friday. A slow moving cold front will approach from the west and pass through on Saturday. High pressure will build Saturday night into the beginning of next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Showers moving across in association with right entrance region of an upper jet streak will slide across early, mostly before 12Z. Then there should be a lull before additional showers in association with a second upper jet streak pass across late this morning and this afternoon, impacting mainly NYC metro and Long Island per latest RAP/HRRR, with scattered activity inland to the north/west. Fcst soundings do show marginal elevated instability, so mentioned isolated thunder. Some showers approaching NYC and the south shore of Long Island could be locally moderate to heavy, but do not expect these to be widespread. The most wiodespread heavy rain, associated with an offshore warm front/tropical predecessor setup to the north of Hurricane Gert, should remain well south of Long Island and NYC. High temps should be in the upper 70s and lower 80s per guidance blend. A high rip current risk continues today for the Suffolk County ocean beaches. A moderate risk elsewhere to start should also become high this afternoon as long period swells from Hurricane Gert begin to arrive.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
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A weak frontal boundary approaching from the NW should move across late, with onshore flow turning SW this evening and then NW after midnight. Any remaining showers, mostly across Long Island/SE CT and also well inland, should end this evening, with dry conditions overnight and low temps in the 60s to lower 70s. As high pressure builds in on Wed, a drying downslope flow and mixing to 800-850 mb in the afternoon should lead to one of the warmer days so far this month, with highs in the upper 80s/lower 90s, at least a couple of degrees above the warmer of the GFS/NAM MOS guidance numbers. The deep mixing should also allow dewpoints to mix out to the upper 50s and lower 60s in most places by afternoon, keeping heat index values close to ambient temps. A high surf advisory may eventually be needed for the ocean beaches for Wednesday as the highest long period swells from Gert approach 7-8 ft.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Long period south to southeast swells will likely be ongoing Wednesday night, and possibly into Thursday, as Gert tracks well east of the forecast waters. See the official NHC forecast for the track of Gert. The persistent longwave trough across eastern Canada will be exiting Wednesday night as the northern stream flow becomes more progressive with a series of shortwaves to affect the area Thursday into Saturday. A rather flat ridge will be left in the wake of the departing trough Thursday with surface high pressure over the area Wednesday night moving offshore Thursday. A return flow sets up ahead of the next system deepening across the upper midwest. There remains some uncertainty with the timing of the shortwaves moving across the northeast Thursday night into Saturday night. A warm frontal boundary approaches from the southwest Thursday night into Friday. With the associated low remaining well to the west, leaned toward a frontal passage during Friday. The area then becomes warm sectored and instability will be increasing, especially inland, away from a marine influence. With the series of shortwaves moving through the upper flow the surface low is slow to track east and northeast with the associated cold front also slow to move through. Timing at this time will be sometime Saturday. A little stronger ridge builds for Sunday into Monday as surface high pressure remains over the northeast.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/... A series of weak waves of low pressure will track east along a warm front south of the region overnight through Tuesday. Mostly VFR for the early morning hours, but MVFR cigs could potentially prevail or at least be temporary before approx 10z with -shra expected through this time. Another period of potential MVFR cigs returns late morning with the potential for it to be tempo or prevailing into the evening hours. More showers will be possible during this time as well. Overall confidence of flight category forecast is only moderate at best. Winds should remain under 10 kt all day. .OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY... .Tuesday night...MVFR or lower conds possible in stratus/fog, particularly away from the city terminals. .Wednesday and Wednesday night...VFR. .Thursday...MVFR conds possible from NYC metro west, with chance of showers. .Thursday night through Saturday...MVFR or lower flight cat possible, with chance of showers and tstms. Best chance for tstms in the afternoon. && .MARINE...
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Have issued SCA for hazardous seas for the ocean waters for tonight through Wed as long period swells from Hurricane Gert arrive and push seas to 5-7 ft. Conditions at the ocean inlets may become rough this afternoon as the first sets of these long period swells arrive. Ongoing swell from hurricane Gert will maintain SCA level ocean seas through Wednesday night. See the official NHC forecast for the track of Gert. A slow moving frontal system will be moving through the waters late Thursday into the weekend. Conditions are expected to remain below small craft levels into the weekend.
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&& .HYDROLOGY...
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Some areas across NYC metro and nearby NE NJ have already seen just over 1/4 inch from rainfall overnight. Another 1/10 to 1/4 inch is likely for NYC and Long Island today, also some interior spots mainly across SW CT. Isolated higher amounts of 1/2 to 1 inch (with similar hourly rainfall rates) may be possible close to the south shore of NYC/Long Island late this morning into this afternoon. Attm think the bulk of these heavier amts will remain just south, but this will have to be watched. A slow moving-frontal system may also bring periods of heavy rainfall Friday into Saturday.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...High Rip Current Risk through this evening for NYZ080-081. NJ...None. MARINE...Small Craft Advisory for hazardous seas from 10 PM this evening to 6 PM EDT Wednesday for ANZ350-353-355.
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&& $$ SYNOPSIS...Goodman/MET NEAR TERM...Goodman SHORT TERM...Goodman LONG TERM...MET AVIATION...JC MARINE...Goodman/MET HYDROLOGY...Goodman/MET

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