Area Forecast Discussion
Issued by NWS Upton, NY

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400 FXUS61 KOKX 132001 AFDOKX Area Forecast Discussion National Weather Service New York NY 401 PM EDT Thu Jun 13 2024 .SYNOPSIS... High pressure moves farther out into the Atlantic through tonight. A cold front approaches Friday and moves across Friday night. High pressure returns for the weekend before sliding offshore early next week. && .NEAR TERM /UNTIL 8 AM FRIDAY MORNING/...
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High pressure will further weaken tonight and move farther out east into the Atlantic. After the decrease of the cumulus and overall mostly clear conditions to start tonight, expecting an increase in clouds from west to east overnight. With some low to mid level Q vector convergence noted more so by the GFS with this not indicated as much with the NAM, have a slight to low end chance of showers late overnight into early Friday morning for parts of the southern coastlines covering the area from coastal CT through coastal NE NJ, NYC and Long Island. In the mid levels, the models do convey weak positive vorticity advection on the backside of the mid level ridge traversing the local region between 2AM and 8AM Friday. With the southerly flow continuing along the coast and increasing clouds late, went with more mild low temperatures. Lows used a combination of NBM and consensus of all guidance, with values mainly in the mid 60s to near 70.
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&& .SHORT TERM /8 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
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Upper level trough moves east into the Northeast with associated jet streak extending from central New England into the Canadian Maritimes on Friday. The right rear quad of the jet stays in Central to Northern New England, so northern parts of the forecast region will have relatively more shear and forcing for more organized thunderstorms. Around 35-40 kt of 0-6 km AGL shear is forecast across the interior sections of the region with values closer to 30 kt across Long Island. For Friday night, the main mid level trough moves across overnight into early Saturday morning. Models are indicating the upper level jet streak to expand Friday night, putting the local area closer to the right rear quadrant of the jet. The 0-6 km AGL shear across the entire region increases to near 40 kt to 45 kt. In terms of instability, surface CAPE values are forecast to reach near 1000 to 1500 J/kg north and west of NYC across the interior areas, with much less CAPE towards the coast. The surface CAPE decreases overall to a few hundred J/kg and shifts to be along the coast for Friday night. The combination of these factors will provide greater potential for severe thunderstorms north and west of NYC with less potential for severe thunderstorms farther east. The SPC has highlighted the interior areas north and west for a slight risk of severe thunderstorms with the rest of the forecast region having a marginal risk of severe thunderstorms. The structure and form of the showers and thunderstorms will likely some combination of clusters and a broken squall line. The broken squall line will be focus of where there could be potentially severe downbursts of wind. The wind is the main threat with these and to a lesser extent that of large hail. Mid level trough approaches Friday with some models indicating a small wavelength shortwave ahead of the main trough that moves in for the late afternoon into evening timeframe. At the surface, a parent low slightly deepens as it moves northeast within Southeast Canada. Its associated cold front will approach the local region. There will likely be a pre-frontal trough developing out ahead of the cold front that will set the stage for initial convection on Friday afternoon. POPs forecast were taken from a combination of CAMs that have some variations with individual clusters of convection but do present a general agreement with a broken line of convection as well as multiple clusters of convection that move across north and west of NYC in the early to mid afternoon and then make their way to the western half of the forecast region late afternoon into early evening. This late Friday afternoon into early Friday evening convection will encompass NE NJ, NYC, Lower Hudson Valley, SW CT and Western Long Island. Thereafter, for mid to late Friday evening, much of the convection is expected to be across Long Island and Southern CT. Forecast does have this convection lingering into the overnight across these areas but thunder chances will decrease as the night progresses. So, expect mainly showers to persist along the coast overnight but diminish in coverage going into early Saturday morning. High temperatures for Friday are for much of the area from the NBM where much of the day is expected to be dry with relatively more sunshine. N&W of NYC covering much of Lower Hudson Valley, interior NE NJ, and interior SW CT, have 3/4 NBM and 1/4 CONSAll for highs, which depicts relatively cooler temperatures than using the NBM alone. Here there are forecast relatively more clouds with showers and thunderstorms starting earlier in the day. The range of high temperatures is from the mid 70s to near 80 along much of the immediate coastline to near 90 for parts of NE NJ and NYC. With dewpoints mainly in the mid 60s, many locations will have max heat index values a few degrees higher than the actual temperature. Still, this gives mostly upper 80s to lower 90s for the max heat index for much of the Lower Hudson Valley, NE NJ, and NYC. Low temperatures for Friday night uses a consensus of raw model data, with a range from the upper 50s to mid 60s.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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**Key Point** * Increasing confidence in a prolonged heat wave mid to late next week. Heat indices may approach or exceed 100F at times. Heights climb on Saturday as the front clears the coast and the upper trough axis shifts east and offshore. Behind it, a 1024 mb surface high builds in from the Great Lakes through the weekend as a subtropical ridge develops and settles over the East, likely producing the first heat wave of the summer locally. Ahead of the heat, quite a comfortable June weekend is expected with abundant sunshine from the nearby high, and afternoon temperatures within a couple degrees of 80. A relatively dry air mass with dew points in the 50s should complement this well. Dry conditions are expected, with some fair weather cu on Saturday, and perhaps increasing cirrus on Sunday. Sunday morning looks even a bit chilly in parts of the region with the high pressure nearby, clear skies, and light flow perhaps allowing efficient cooling overnight yielding upper 40s across the far interior and the LI Pine Barrens. Utilized a MAV/MET blend over blended guidance to better capture this. Ridging then builds late this weekend and early next week with a 590+ dm ridge developing over the Southeast in response to a vigorous trough swinging onshore the Pacific Northwest. This ridge amplifies as it settles over the East mid to late next week, and global ensemble means peg H85 temperatures around 20C much of this time. This should yield temperatures into the low to mid 90s away from the coast by next Wednesday, if not Tuesday. Persistent southerly or southwesterly flow around the offshore surface high will advect in some higher dew pts, likely into the 60s, leading to heat indices potentially approaching or exceeding 100F at times. This could eventually necessitate heat headlines as we move closer. Given the potential duration of the heat, it`ll be important to take precautions to protect one`s health, particularly those without effective cooling and/or adequate hydration. Some heat-sensitive industries and infrastructure will likely be impacted by the extent of this heat as well.
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&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/... VFR through most of the TAF period. A cold front approaches from the NW late Friday bringing unsettled weather late Friday into early Saturday morning. Best chance of TSRA 18-22z Friday KSWF and 20-00z Sat across city terminals. Heavy rain and gusty winds possible in any TSTM Friday. S-SW Winds 10-15kt with gusts to 25kt at the coast continue into early evening. Tonight, gusts diminish but winds are expected to remain around 10 kt overnight into Friday morning. Stronger winds possible in vicinity of stronger TSTMs Friday afternoon and evening. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... No unscheduled amendments likely through 18z Friday. OUTLOOK FOR 18Z FRIDAY THROUGH MONDAY... 18z Friday: MVFR or lower possible in showers/tstms late afternoon or evening. Saturday through Monday: VFR. Tuesday: VFR expected. CHC of MVFR in afternoon SHRA/TSTM mainly NW of city terminals Detailed information, including hourly TAF wind component forecasts, can be found at: https:/www.weather.gov/zny/n90 && .MARINE...
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More southerly flow this afternoon with gusts expected to 20-25 kt. The gusts will be occasional as warmer air moving in aloft will limit mixing. So, do not have SCA for any of the forecast waters as the 25 kt gusts are just expected to be occasional. Seas on the ocean expected to remain below SCA thresholds and well below SCA thresholds for non-ocean waters. Wind subside tonight with wind gusts on Friday to near 20 kt. Winds subside again Friday night with wind direction eventually becoming more NW. Sub SCA conditions are expected on all waters this weekend thru early next week.
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&& .HYDROLOGY...
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For much of the area, there is a marginal risk of flash flooding. Would expect mostly minor poor drainage flooding in low lying and urban areas but localized flash flooding cannot be ruled out. The progressive nature of the thunderstorms is expected to keep much of any flooding more minor with fast movement of the thunderstorms. Will just have to monitor potential for multiple rounds of thunderstorms. The HREF shows that north and west of NYC is there is potential (around 10 percent chance) for hourly rain rates of 1 inch per hour late Friday afternoon into early Friday evening. The chances are less than 10 percent for the rest of the area for 1 inch per hour rainfall rates. The total rainfall amounts from Friday afternoon through Friday night range from around 0.5 to 0.75 inch to near 1 to 1.5 inches. NYC is around 1 inch for the storm total rainfall forecast. Locally higher amounts will be possible. No hydrological issues are expected this weekend through mid next week.
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&& .TIDES/COASTAL FLOODING... There remains a moderate rip current risk this afternoon for the ocean beaches, and a high risk for most ocean beaches Friday. Eastern Suffolk beaches are expected to have a moderate rip current risk on Friday. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JM/DR NEAR TERM...JM SHORT TERM...JM LONG TERM...DR AVIATION...IRD MARINE...JM/DR HYDROLOGY...JM/DR TIDES/COASTAL FLOODING...