Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 211404 CCA AFDOKX Area Forecast Discussion...CORRECTED National Weather Service New York NY 1004 AM EDT Wed Jun 21 2017 .SYNOPSIS... A series of frontal systems will impact the area through early next week. The first will approach this afternoon and move through this evening, followed by another from Friday afternoon into Saturday, and then another late Sunday into Sunday night. Low pressure will pass off to the southeast Monday into Monday night, possibly followed by yet another weak frontal passage on Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The forecast has been updated to capture the latest trends in cloud cover, temps and dewpoints. High temperatures over the northern half of Long Island have been bumped up a couple of degrees. 12z OKX sounding otherwise supports current high temp forecast. Also added in a chance of showers over portions of the Lower Hudson Valley as per latest radar trends. A frontal boundary over the eastern portion of the forecast area is expected to dissipate today. Meanwhile, a mid level shortwave will be approaching from the west this afternoon. Additional synoptic lift may be supplied by an approaching left exit region of a jet streak aloft. This lift will combine with upwards of 1000 J/KG SBCAPE to produce isolated to scattered thunderstorms this afternoon. 12 OKX sounding reveals a dry sub-cloud layer, and this is expected to continue through the rest of the day. Strong deep shear and steepening low level lapse rates could produce a few isold strong to even severe tstms. Concur with SPC marginal risk given steep low level lapse rates, inverted-V look to fcst soundings, and deep layer shear. WINDEX (dry microburst wind index) values reach 50-55 kt late this afternoon, and even MDPI (wet microburst day potential index) values increase to 0.75 across Long Island per RAP toward 00Z, supporting the wind threat with stronger storms. Will keep mention of this in HWO. There is a high risk for rip current development at Suffolk County ocean beaches and a moderate risk for NYC and Nassau county ocean beaches through this evening.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Convection should still be ongoing across NYC metro and Long Island through about sunset, then convective threat should wane with the loss of heating and with the front pushing through. Not much in the way of an air mass change tonight and Thursday despite the fropa. H8 temps remain right around 12-14C next 24 hours, with a WAA pattern developing thereafter. Dry weather will prevail with rising heights. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... An active northern branch of the polar jet will remain across the northern tier of the country, with the mean upper trough residing over the Northern Plains through Friday, then extending into the Northeast this weekend and early next week. This will allow for several frontal systems to impact the area during the time, the first Friday into Saturday, and then another late Sunday into Sunday night. After a warm frontal passage Friday morning, temps should warm up well into the 80s and lower 90s, with dewpoints increasing to the upper 60s. A few tstms are possible in the warm sector, but timing/areal coverage are in question, as models generally indicate better instability from late morning into early afternoon, and disagree on timing of the approach of a southern branch mid level shortwave trough well in advance of the remnants of Tropical Storm Cindy to produce lift. Any storms that do develop would have potential to be strong to locally severe, with MLCAPE over 1000 J/kg and mid level flow up to 35 kt, along with some veering with height. This first front looks to stall over the area, with another chance for showers/tstms on Saturday. Areal coverage will depend on the northward extent of any residual energy from the remnants of Cindy to provide lift. If this forcing remains suppressed per ECMWF, areal coverage would be isolated at most, but could end up more widespread per farther north/slower GFS. Instability looks more limited with the second frontal passage on Sunday, and moisture will be more lacking, so have only mentioned isolated showers. ECMWF amplifies the mean upper trough more than the GFS over the weekend, enough to induce somewhat stronger low development along the frontal boundary to the south that would track closer to the area. As a result have mentioned chance for showers from Mon into Mon night. Temps should be several degrees above average through the weekend, then return to near average early next week. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... A cold front moves cross the area this afternoon and early this evening, followed by weak high pressure building in through Thursday morning. Highly likely VFR through the TAF period. A brief period of MVFR is possible this afternoon/evening with any stronger convection at any given terminal. Still appears there will be isolated to scattered showers and thunderstorms at area terminals this afternoon and evening. Confidence at this time is only sufficient to carry a VCTS in the TAFS (VCSH KGON). W-WSW winds back to the S-SW this afternoon. Should see seabreeze enhancement at KJFK/CT/Long Island terminals. Gusts this afternoon mainly 20-25kt with peak gusts 25-30kt mainly at coastal terminals. Higher gusts are possible with any stronger convection. Winds subside after 23 to 01z, then become light and variable later tonight. 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: SW winds G20KT expected to develop after 16-17z. S seabreeze of 20G25KT likely to develop after 19-20z with isolated gusts to 30 kt possible. Low chance of a shower/tsra between 20z and 00z...with accompanying potential for west winds G35-40KT. KLGA TAF Comments: SW winds G20-25KT expected to develop after 16-17z. Low chance of a shower/tsra between 20z and 00z...with accompanying potential for west winds G35-40KT. KEWR TAF Comments: WSW-W winds G15-20KT expected to develop after 16-17z. Isolated gusts to 25 kt possible. Low chance of a shower/tsra between 20z and 00z...with accompanying potential for west winds G35-40KT. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Comments: WSW-W winds G15-20KT expected to develop after 16-17z. Isolated gusts to 25 kt possible. Low chance of a shower/tsra between 20z and 00z...with accompanying potential for west winds G35-40KT. KHPN TAF Comments: W winds G15-20KT expected to develop after 16-17z. Isolated gusts to 25 kt possible. Low chance of a shower/tsra between 20z and 00z...with accompanying potential for west winds G35-40KT. KISP TAF Comments: SW winds G20KT expected to develop after 16-17z. SSW seabreeze G20-25KT likely to develop after 20-21z with isolated gusts to 30 kt possible. Low chance of a shower/tsra between 21z and 01z. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SUNDAY... .Thursday...VFR. Afternoon coastal sea breezes. .Thursday night-Friday night...Chance MVFR or lower and of mainly afternoon showers/thunderstorms. SW winds G15-20KT possible. .Saturday...CHC early -shra/MVFR, otherwise VFR. NW winds G20-25KT possible. .Saturday night-Sunday...VFR. && .MARINE... Seas are expected to be mainly below 5 ft on the ocean waters today, however near shore winds are expected to reach SCA levels this afternoon. A moderate SW flow could also bring seas back up to marginal levels later this aftn and eve so have extended the SCA through 06z tonight. Elsewhere...with the exception of eastern Long Island Sound...where confidence isn`t as high...near shore gusts around 25 kt are SCA conditions will be possible on the ocean Friday into Saturday as S-SW flow increases to near/just over 15 kt with the approach of a cold front, building seas to near 5 ft. && .HYDROLOGY... Any tstms that develop today should be fast moving. No flooding impacts are anticipated through Sunday. && .TIDES/COASTAL FLOODING... With the approach of a new moon, occurring Friday evening, astronomical tides will be running very high, especially during the high tide cycles Thursday, Friday, Saturday evening. Less than 1 ft of surge is needed for minor flooding...and in some cases less then 1/2 ft...during these evening high tide cycles. The expected S/SW flow is not favorable for surge build-up, but southerly swells and a running anomaly will likely be enough for minor coastal flooding along the south shore back bays of Nassau with each evening tidal cycle. Brief and localized minor coastal flooding will also be possible in Jamaica Bay and Western Long Island Sound during this time. && .EQUIPMENT... KOKX weather radar is scheduled for maintenance starting this Friday June 23rd for a period of 3 days. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...High Rip Current Risk until 9 PM EDT this evening for NYZ080- 081. NJ...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ335- 338-340-345-355. Small Craft Advisory until 2 AM EDT Thursday for ANZ350-353. && $$ SYNOPSIS...24/Goodman NEAR TERM...JC/24 SHORT TERM...24 LONG TERM...Goodman AVIATION...Maloit/NV MARINE...24/Goodman HYDROLOGY...24/Goodman TIDES/COASTAL FLOODING... EQUIPMENT...

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