Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 132002 AFDOKX Area Forecast Discussion National Weather Service New York NY 402 PM EDT Sun Aug 13 2017 .SYNOPSIS... High pressure over the area moves offshore tomorrow. Weak low pressure passes to the south Monday night. A cold front approaches from the north Tuesday before dissipating Tuesday night. High pressure builds into the region Wednesday and slides offshore Wednesday night. A slow moving frontal system impacts the region Thursday through Saturday. High pressure builds in for the end of next weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Most significant element to the evening`s forecast is the continuation of the high risk of rip currents across Nassau and Suffolk County ocean beaches. There is a moderate risk of rip currents for the NYC beaches. Cloud cover is gradually decreasing across the area in response to increasing subsidence aloft. The remaining strato cu will slowly diminish tonight with the loss of diurnal heating and the advection of lower dew points into the area. With high pressure building, winds will continue to decrease, which in combination with clearing skies will create favorable conditions for radiational cooling. Low temperatures will be a few degrees below climatological normals with the exception of the metropolitan areas.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
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High pressure slides through the area on Monday, with winds gradually shifting around to a more onshore component, which should act to keep temperatures closer to climatological normals. Mid and high level cloud cover will gradually increase through the day ahead of a short wave approaching from the west. Increasing divergence aloft will allow an area of low pressure to deepen offshore of the area Monday night, with isolated rain showers possible across coastal areas as it passes to the east. There are significant differences in how far north this system reaches, which could impact later forecast updates. For now, maintained a more southern trajectory keeping the majority of the area dry. There is a moderate risk for the development of rip currents at the ocean beaches Monday.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/... Long Island will be on the northern fringe of a precipitation shield associated with a low passing east of the mid Atlantic coast early Tuesday morning. So will have slight chance probabilities through 12Z, for light showers. There are differences as to the northern extent of the precipitation with the GFS dry and the ECMWF farther to the north. Otherwise an upper low remains over eastern Canada with a shortwave rotating into the northeast for later Tuesday with a weak surface cold front approaching. The shortwave will be moving into a flat ridge and the southern push of the shortwave is uncertain at this time. Any precipitation looks to be mainly diurnally driven for Tuesday, and will be mostly across the north and west. Will bring slight chance probabilities into central New Jersey and the metro NY area, however, this is highly uncertain. The best instability and additional lift with and upper jet moving through the Hudson Valley Tuesday afternoon will be across the far northern tier. So will have wording of isolated thunderstorms. The cold front that approaches looks to reach as far south as Long Island before becoming stationary and dissipating as heights begin to rise after 00Z Wednesday. A rather weak ridge builds Tuesday night into Wednesday. Again there is uncertainty as to how quickly the ridge weakens as a blocking pattern will be in place and there in uncertainty as to the timing the northern stream becomes more active. Leaned toward consistency with the previous forecast and bring precipitation probabilities back into the area Thursday. Although, as stated earlier, this may be too quick and there are solutions that hint the precipitation is delayed until Friday. The northern flow will be weak and the next shortwave, and associated surface wave, will be rather slow to progress through the northeast. Therefore, will have a prolonged period of chances for precipitation from Thursday into Saturday. With the uncertainty have capped probabilities at chance. Dry weather returns for next Sunday as the upper flow again become flat with weak height rises. The temperatures Tuesday through next weekend will be near seasonal normals. && .AVIATION /20Z SUNDAY THROUGH FRIDAY/... High pressure builds in through tonight and offshore Monday. VFR conditions are forecast through the TAF period. Winds will be relatively light most of the period and 10 kt or less. The exception to this is this afternoon with some gusts to near 15 kt. NW flow becomes more W-SW by early evening and the becomes northerly late tonight. More easterly to southerly flow develops Monday. Low chance for 180-210 direction winds for KJFK late this afternoon into early evening, 21-23Z. .OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY... .Monday...VFR. .Tuesday...Mainly VFR. MVFR possible with isolated showers and tstms NW of NY/NJ metro in the afternoon into early evening. .Tuesday mid evening-Wednesday night...VFR. .Thursday...Mainly VFR. MVFR possible with low chances of showers and thunderstorms in the afternoon mainly N/W of NY/NJ metro. .Thursday night-Friday...MVFR possible. A chance of showers. A slight chance of thunderstorms Fri. && .MARINE... Seas around 4 to 5 feet on the eastern ocean waters will gradually subside overnight as high pressure builds across the area. A weak surface pressure gradient force across the waters Monday through Friday will keep winds and seas below small craft advisory levels. The exception will be during Wednesday, seas may be around 5 feet on the ocean waters east of Moriches Inlet, as a system moving well east of the forecast waters generates an east to southeast swell. && .HYDROLOGY... No hydrologic impacts are expected through Sunday. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...High Rip Current Risk until 8 PM EDT this evening for NYZ080- 081-179. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 8 PM EDT this evening for ANZ350-353. && $$ SYNOPSIS...MD/MET NEAR TERM...MD SHORT TERM...MD LONG TERM...MET AVIATION...JM MARINE...MD/MET HYDROLOGY...MD/MET

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