Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 212000 AFDOKX Area Forecast Discussion National Weather Service New York NY 400 PM EDT Mon Aug 21 2017 .SYNOPSIS... High pressure over the region moves offshore today and tonight. A cold front approaches from the west Tuesday and passes through Tuesday night into Wednesday morning. High pressure builds in behind the cold frontal passage on Wednesday and remains in control through the end of the week with a much drier and cooler airmass. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... High pressure will be situated offshore, however mid-level shortwave lift is expected to enter from the west tonight. This will bring chances of showers and thunderstorms across the area. RH above 850mb should limit overall chances, so will go with just a slight chance. A MAV/NAM MOS blend looked good for low temperatures, and muggy conditions should prevail with dewpoints around 70. There is a moderate risk of rip currents at Atlantic beaches through this evening. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... The shortwave should still be over the tri state area during the morning, so cannot completely rule out a shower/storm during this time. In the afternoon, subsidence behind the shortwave will work against convective development. A surface trough over the interior could still provide a focus for convergence. Will go with a slight chance to chance for showers and storms, with the higher chances over the interior. Some thunderstorms may be strong to marginally severe with bulk shear of about 30 kt and sufficient CAPE values forecast. 850mb temps are forecast to be around 18-19C which should translate to high temperatures in the low-mid 90s for the typically warmest spots across the city, NE NJ and adjacent areas given the expected cloud cover and wind flow. With winds at a southerly component and 850mb dewpoint temps forecast at mostly 14-17C, chances of mixing out and having surface dewpoints drop more than a degree or two in the afternoon are slim. Heat index values are therefore expected to range in the 90s to around 100. With Wednesday`s heat index values expected to fall short of all advisory criteria, will issue a heat advisory for the 1-day heat index criteria of 100. Will go with the advisory over the city, southern Westchester County and parts of NE NJ. A cold front moves into the region Tuesday night with better chance of showers and thunderstorms across the area. CAPE will drop due to the loss of daytime heating but lift and shear increase ahead of the front. Strong to marginally severe thunderstorms will be possible once again. The steering flow should be quick enough to mitigate chances of flash flooding, but with high moisture content around, minor nuisance/urbanized flooding is possible. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... The cold front will slowly push east of the area on Wednesday with lingering showers and perhaps a few embedded tstms mainly across the eastern half of Long Island and southern CT. Skies clear Wed evening with a much cooler airmass arriving. Canadian high pressure builds into the region Thursday through early next week, providing dry and sunny conditions. Temperatures will remain below normal as highs only reach the 70s to near 80 each day. There could be some isold showers/tstms on Sunday as an upper trough moves through the Northeast. Most model guidance has the upper level energy passing to the north of the CWA so have not included in the current forecast, however this may change in subsequent forecasts. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... Mainly VFR through the TAF period. An isolated shower or tstm possible tonight from the NYC metros north/west. Have only mentioned VCTS as chances are on the lower side. Bigger forecast problem for tonight centers around late night reductions in cigs/vsby. Think KISP/KGON/KSWF most likely to see reductions to at least MVFR, but cannot totally rule it out at the the NYC metros some time between 09Z-12Z give or take an hour. Sea breezes are in at KJFK/KLGA/KHPN/KISP/KBDR/KGON, and should increase to near 15 kt at KJFK. They may just barely make it to KEWR/KTEB. Winds diminish tonight, then expect both stronger southerly coastal sea breezes and SW inland flow Wed afternoon, with gusts aoa 20 kt likely. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Low chance for BKN010-015 MVFR cigs from 09Z-12Z. KLGA TAF Comments: Low chance for BKN010-015 MVFR cigs from 09Z-12Z. KEWR TAF Comments: Low chance for BKN010-015 MVFR cigs from 09Z-12Z. KTEB TAF Comments: Low chance for BKN010-015 MVFR cigs from 09Z-12Z. KHPN TAF Comments: Low chance for BKN010-015 MVFR cigs from 09Z-12Z. KISP TAF Comments: No unscheduled AMD expected. .OUTLOOK FOR 18Z TUESDAY THROUGH FRIDAY... .Tuesday Afternoon...Mainly VFR. Isolated/scattered afternoon showers/tstms possible NW of NYC, especially KSWF. S winds G25-28KT at KJFK/KISP, and S-SW winds G20-25KT elsewhere. .Tuesday Night...Showers/tstms with MVFR or flight cat likely, especially lower Hudson valley/CT terminals. S-SW winds G25KT at KJFK/KISP, and G20KT elsewhere mainly before midnight outside of tstms. .Wednesday...Lingering showers/tstms possible in the morning, then becoming VFR. W-NW winds G15-20KT. .Wednesday Night-Saturday...VFR. && .MARINE... Sub-sca conditions continue tonight into Tuesday morning with a relatively weak pressure gradient in place. As a cold front approaches, south to southwest winds increase. SCA over the ocean waters remains, but have added the South Shore Bays to the SCA for Tuesday afternoon and night as gusts should reach at least 25 KT. Occasional gusts to 25 kt will be possible over all other non-ocean waters. Small craft conditions may need to be extended into Wednesday on the ocean waters due to lingering elevated seas. Sub-advsy conds are then expected through the weekend with tranquil weather. && .HYDROLOGY... Showers and thunderstorms Tuesday and Tuesday night may cause minor nuisance/urbanized flooding. No widespread hydrologic impacts are forecast through the rest of the week. && .TIDES/COASTAL FLOODING... Tides are running high astronomically. For the South Shore Bays, there is the potential for water levels to just reach the minor coastal flooding benchmarks with this evening`s high tide. Thinking is that it`s more likely that all areas fall just short of flooding with at most only a spot or two perhaps touching minor flooding benchmarks. Will therefore not issue a statement at this time. With a stronger onshore flow on Tuesday, there is a better chance for some spots along the South Shore Bays to reach minor flooding. Too soon to issue any products for this, so will allow subsequent shifts to assess trends and issue any statements or advisories as needed. . && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory from noon to 6 PM EDT Tuesday for NYZ071>075-176- 178. NJ...Heat Advisory from noon to 6 PM EDT Tuesday for NJZ004-006- 104>108. MARINE...Small Craft Advisory from 3 PM Tuesday to 6 AM EDT Wednesday for ANZ350-353-355. Small Craft Advisory from 3 PM Tuesday to midnight EDT Tuesday night for ANZ345. && $$ SYNOPSIS...JC NEAR TERM...JC SHORT TERM...JC LONG TERM...24 AVIATION...Goodman MARINE...JC/24 HYDROLOGY...JC/24 TIDES/COASTAL FLOODING...JC is the U.S. government's official web portal to all federal, state and local government web resources and services.