Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 220149 AFDOKX Area Forecast Discussion National Weather Service New York NY 949 PM EDT Fri Jul 21 2017 .SYNOPSIS... Hot and dry weather expected through Saturday. A weak cold front will settle south of the area tonight. This front will remain nearly stationary south of the area Saturday and Saturday night. A frontal boundary will be in the vicinity Sunday morning, and remain in the area Sunday, as high pressure builds to the north. The high drifts off the northern New England coast Sunday as a wave of low pressure moves eastward along to the boundary into Tuesday. High pressure will follow late Tuesday and Wednesday. Another wave of low pressure follows for Wednesday night into Friday through Thursday. A cold front will approach Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Forecast generally on track. A few isolated showers have developed north and west of the CWA. Can not rule out a shower or two moving across portions of NE NJ and the Lower hudson valley. otherwise, expecting a dry night. Have included isolated showers in the forecast for the next couple of hours. Fast zonal westerly flow in the mid levels will help push a weak cold front to south of Long Island late tonight into early Saturday. The front itself should come through dry. Winds will become light and variable tonight. Lows will be on the warmer side with the clouds increasing, mid 60s in rural locations to upper 70s in the NYC urban heat island. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Fast zonal westerly flow aloft will remain Saturday and Saturday night. The heights will be lowering slightly overall during this timeframe. At the surface, the front will become stationary south of Long Island. A shortwave aloft will help with development of low pressure along the front that will move in Saturday night into early Sunday. Another hot dry day is expected with a little more humidity as well, pertaining to absolute humidity here as diagnosed from slightly higher dewpoints. A weaker pressure gradient will result in lighter winds during the day, giving way to typical sea breeze circulations. The NYC Metro area is still going to initialize Saturday with relatively warmer temperatures. Therefore, taking this into account, heat advisory criteria is expected to be nearly met for the greater NYC Metro Area encompassing adjacent zones in Northeast NJ. Cannot rule out some 95 degree heat indices within the aforementioned area but majority of heat indices probably in the 91 to 94 range. For Saturday night, the weather becomes more unsettled with the increasing chances for showers and thunderstorms. However, the more recent model trends show a southward trend to showers and thunderstorms with the wave of low pressure along the front. Omega increases substantially at 700mb providing extra lift despite marginal instability. A more southward shift so that the highest chances Saturday night are along the southern coasts of the forecast region and NYC. High precipitable waters will be present so heavy rain will be possible with some thunderstorms. In addition, gusty winds are possible with some thunderstorms depending on the strength of the wave of low pressure. Lows taken from warmer guidance of GMOS and MAV, ranging from the upper 60s to mid 70s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... There remains some uncertainty as to the track of an ongoing convective complex at the beginning of the forecast period, that will be moving out of the upper midwest. At this time the trend has been for high pressure to be building to the north pushing a frontal boundary farther to the south. As a result the forecast of the complex is also farther to the south Sunday morning. So have lowered the probabilities overall Sunday, with the lowest chances to the north. If the high pushes farther to the south the area may be dry through Sunday. Then a shortwave will be moving through the northern stream, across the Great Lakes Sunday into Sunday night, and the move slowly through the northeast Monday into early Tuesday as ridging builds over the western Atlantic. Again there remains some uncertainty with the timing of this shortwave. Also there is uncertainty as to how much destabilization will occur Sunday. With an easterly flow developing as the surface high builds to the north, the area will become more stable under a marine influence. So while there will be marginal destabilization and will keep mention of thunder, and with the timing more Sunday night into Monday, there is more uncertainty with the development of severe weather with these storms. Weak ridging will build to the west later Tuesday into Wednesday as high pressure builds to the west. The upper flow becomes progressive Wednesday as the western Atlantic ridge weakens and drifts east. Yet another shortwave and cold front will affect the area Wednesday night into Friday. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... VFR through the period. Mainly W winds except NYC and coastal terminals which will be more of a W-SW direction at around 10 kt this evening. Light northerly flow late tonight. Local sea breezes possible again on Saturday at KJFK, KGON, KISP, and KBDR for allow for some variability in wind direction. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: No unscheduled amendments expected. KLGA TAF Comments: No unscheduled amendments expected. KEWR TAF Comments: No unscheduled amendments expected. KTEB TAF Comments: No unscheduled amendments expected. KHPN TAF Comments: No unscheduled amendments expected. KISP TAF Comments: Sea breeze continues to meander in the vicinity of the airport allowing for some variability in wind direction. .OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY... .Saturday Afternoon...VFR. .Saturday Night-Tuesday AM...Episodes of showers and thunderstorms with MVFR or lower conditions possible. .Tuesday PM...Conditions improving to VFR. .Wednesday...VFR. && .MARINE... A weak pressure gradient overall will keep winds and seas below SCA (Small Craft Advisory) levels of 25 kt and 5 ft through Saturday night. However, there is the potential for thunderstorms Saturday night that could result in larger waves and higher winds, particularly across the ocean. Winds will remain below small craft levels Sunday through Wednesday. However, ocean seas may build to marginal small craft levels Sunday night into Monday as an easterly flow develops and increases Sunday into Monday night. Then seas are expected to subside for Tuesday and Wednesday. && .HYDROLOGY... The heaviest precipitation from a convective complex will be mainly to the south of the region by Sunday morning, with additional rainfall of little to none across the northern zones to around a quarter of an inch across northeastern New Jersey, eastward across NYC and Long Island. At this time the chances of urban and poor drainage flooding have diminished. Additional rainfall is possible Sunday night into Tuesday. Hydrologic impacts are not expected at this time. && .TIDES/COASTAL FLOODING... An approaching new moon (Sun) will have tides running high this weekend into early next week. Positive tidal departures of 1/2 to 1 ft will be needed for minor flooding during the night time high tides during this time. Minor flooding is possible starting with the Saturday Night high tide cycle, mainly in the western south shore bays of LI. A bit more widespread minor flooding is possible Sunday Night if an e/ne flow develops ahead of an approaching frontal system. The threat for minor flooding could continue into Monday. && .CLIMATE... Saturday will mark the 4th consecutive day of 90+ degrees temps for much of the NYC/NJ urban corridor. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory from noon to 6 PM EDT Saturday for NYZ072>075- 176-178. NJ...Heat Advisory from noon to 6 PM EDT Saturday for NJZ006-104- 106-108. MARINE...None. && $$ SYNOPSIS...JM/MET NEAR TERM...BC/JM SHORT TERM...JM LONG TERM...MET AVIATION...IRD MARINE...JM/MET HYDROLOGY...JM/MET TIDES/COASTAL FLOODING... CLIMATE...

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