Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 212148 AFDOKX Area Forecast Discussion National Weather Service New York NY 448 PM EST Sat Jan 21 2017 .SYNOPSIS... Weak high pressure slides east tonight. A deepening low pressure will approach the Tennessee River Valley from the southern plains on Sunday and will reach the southern Mid Atlantic region by Monday morning, while high pressure builds southeast into the Canadian Maritimes. The low will intensify into a significant coastal storm as it moves up the coast toward the area Monday through Tuesday. High pressure builds for Wednesday as the coastal low departs towards New England. A cold front slowly approaches the area from the west, moving through late Thursday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Weak upper level ridging slides east tonight. Clouds have started to clear out across portions of the forecast area late this afternoon. However, with plenty of low level moisture in place and a light flow, expect low clouds and patchy fog to re-develop tonight. There is a chance that some of the fog may become dense tonight. This will need to be monitored for the need for any dense fog advisories. Temperatures tonight fall into the 30s and 40s. A MAV/MET/ECS blend was used. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Significant coastal storm expected Sunday Night into Tuesday with potential high wind...heavy rain...and coastal impacts. Upper level system will close off over the southern plains tonight and then negatively tilt up the east coast Monday into Tuesday. The result will be strong low pressure tracking through the southern states this weekend...towards the Mid Atlantic Mon morning...with a coastal low developing and tracking s/se of LI Mon into Mon Night. Models in better agreement with the synoptic fields...with reduced but still some spread in the track/timing of the closed upper low as it moves up the coast...which is playing out in model spread on track/speed of the approaching surface low Mon/Tue. This is particularly seen in the timing/location of coastal low development late Mon and then SE of the region Mon Night...and how quickly the strong easterly jet moves ne of the region. 12z GFS/NAM have trended quicker with ECMWF trending a bit slower...which leaves uncertainty in how quickly winds and precip taper off late Mon/Mon eve. Have maintain slower previous forecast timing based on this wavering and blocky pattern development. Potential continues for multiple impacts of strong winds, heavy rain (period of wintry mix NW) and minor to locally moderate coastal flooding, with likelihood of occurrence in that general order. In terms of winds....high confidence in wind advisory of 30 to 40 mph with gusts 50-60 mph for the coast Mon...with moderate potential for high wind gusts of 60-65 mph with an easterly jet 5-6 std above climo and peaking around 70-75 kt at 925 hpa. Farther north/west, wind gusts will likely approach or exceed wind advisory criteria, reaching 40- 50 mph, particularly higher terrain. High wind watch remains in effect for coast. Peak winds could begin as early as mid Mon morning and linger well into Mon eve. See coastal flood sections for potential coastal impacts. In terms of heavy precip...PWATs of 3-4 stds above normal continue to be signaled as the system taps into tropical connection to the Caribbean and Eastern Pacific. Coastal front development (E LI?) and orographic lift over western faces of hill terrain will be favored for heaviest rainfall amounts in moist easterly flow. Embedded convection not out of the question late Monday/Mon eve ahead of approaching closed low and with warm conveyor belt feeding into the region. Based on ensemble/operational output...likelihood for 1 to 3 inches of qpf with higher amounts possible. NAM/GFS indicating low-level cold air damming signature undercutting 750-850 hpa warm nose Sunday night through Monday aft over the region. Based on strong dynamics and deep enough cold layer well N&W of NYC Mon...sleet could mix in briefly at the coast...with more prolonged rain/sleet or even plain sleet across NW hills Mon morn/aft. A light sleet accumulation is possible across interior portions of NE NJ...Lower Hud...and Southern Ct...particularly the NW hills. Winds and heavy precip should fall off Late Mon/Mon Night from sw to e as llj moves ne...but how quickly is still in question. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Slow moving coastal storm passes Tuesday. With the Upper trough and associated upper level low remaining over the region, will continue to mention likely POPs through the day, before gradually ending Tuesday night. Generally looking at mostly dry conditions Wednesday through Saturday. A cold front will bring cooler conditions for the end of the long term period. Expect highs Tuesday through Thursday in the middle and upper 40s, a good 10 degrees above normal. Friday and Saturday, high temperatures fall back to near normal, with high in the upper 30s and lower 40s. && .AVIATION /21Z SATURDAY THROUGH THURSDAY/... Weak high pressure will move southeast of the area tonight as a warm front approaches from the south. Low level clouds are now moving back north across the area and are forecast to redevelop with the approach of sunset and become widespread LIFR/IFR by 04z tonight with VSBY around 1/2SM in fog. Surface winds are forecast to be light and variable, 5 kt or less until 15z Sunday when NE winds of 5-10 kt develop. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 .OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY... .Sunday Afternoon-Night...MVFR or lower in light rain, then moderate rain at night. NE winds G20-30KT by late day, and G30-40KT later at night. LLWS possible late Sunday night. .Monday-Monday Night...IFR conditions with LLWS. Moderate to heavy rain is expected at all terminals, except perhaps KSWF where some snow or sleet may mix with the rain. ENE winds 25-35KT with G40-50KT, stronger near the coast. .Tuesday-Tuesday night...Rain tapering off by afternoon with improving ceilings into the evening. NW winds G25-35KT, highest in the morning. .Wednesday and Thursday...VFR. SW Winds 15-25 kt. && .MARINE... Tranquil conditions on the area waters tonight. Only headline will be a dense fog advisory, for the ocean waters, as visibilities drop to 1 mile or less tonight. The dense fog advisory is in effect until 14z. Unsure just how far the dense fog spreads overnight, so this will need to be monitored in case it needs to be expanded into the non-ocean waters. An intensifying storm moving up the coast early next week will likely bring storm force gusts to the ocean and LI Sound...with potential for gusts even on nearshore waters Sunday night into Monday night. These winds have the potential to build seas to as high as 20 ft could occur on the ocean waters, and 5-10 ft on LI Sound. Winds start to diminish on Tuesday, however seas will take a while to fall below 5 ft. Expect a prolonged period of small craft conditions on the area ocean waters. && .HYDROLOGY... Likelihood of 1 to 3 inches, with locally higher swaths possible with a coastal storm Sun night into Monday...with heaviest rainfall Mon aft/eve. If high end rainfall amounts are realized...this will bring a threat for moderate urban flooding and minor small stream flooding in NE NJ/Lower Hud Valley. This would be exacerbated by coincidence of high tide with the heavy rain Mon eve. Rises on larger rivers would be likely...but at this point the potential for minor flooding appears slight. && .TIDES/COASTAL FLOODING... A strong coastal storm will likely cause 2 successive high tide cycles of minor coastal flooding Sunday Night into Monday Night...with potential for moderate coastal flooding for southern and eastern portions of LI with the Monday evening high tide. A coastal flood watch has been issued to address this threat. Minor coastal flooding could linger for the southern and eastern bay areas for the Tuesday morning high tide cycle. An ensemble of guidances is showing potential for surge to build to 2 to 3 ft Mon am...and 3 1/2 to 4 1/2 ft by Monday evening. The highest threat for coastal impacts will be for flood prone locales along the south shore bays of LI/NYC...eastern bays of LI...lower NY/NJ harbor including tidally affected rivers...and western Li Sound. The other concern will be for widespread dune erosion and localized washovers at Atlantic ocean beaches from elevated waters levels and an east to west sweep of 8 to 12 ft surf Mon into Tue. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...High Wind Watch from late Sunday night through late Monday night for CTZ009>012. NY...Coastal Flood Watch from Monday afternoon through Monday evening for NYZ079>081-179. High Wind Watch from late Sunday night through late Monday night for NYZ071>075-078>081-176>179. NJ...High Wind Watch from late Sunday night through late Monday night for NJZ006-106-108. MARINE...Storm Warning from 1 AM Monday to 1 AM EST Tuesday for ANZ330- 335-338-340-345-350-353-355. Dense Fog Advisory until 9 AM EST Sunday for ANZ350-353-355. && $$ SYNOPSIS...BC/NV NEAR TERM...BC SHORT TERM...NV LONG TERM...BC AVIATION...GC MARINE...BC/NV HYDROLOGY...NV TIDES/COASTAL FLOODING...NV

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