Area Forecast Discussion
Issued by NWS Upton, NY

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038 FXUS61 KOKX 220248 AFDOKX Area Forecast Discussion National Weather Service New York NY 948 PM EST Sat Jan 21 2017 .SYNOPSIS... Weak high pressure moves east overnight. A low pressure system will approach the Tennessee River and Ohio Valleys from the southern plains Sunday, reaching the southern Mid Atlantic region by Monday morning. Meanwhile, 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/... Widespread dense fog was across the region as a saturated low layer under an inversion remains overnight and into early Sunday morning. At the upper levels weak ridging moves east overnight. Winds will be near calm amd with little advection temperatures and dew points are likely to remain near steady through the overnight. This saturation is depicted in NARRE/HRRR and NAM profiles. A dense fog advisory remains in effect into Sunday morning. && .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. Strong 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. 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/SE CT?) and orographic lift over western faces of hill terrain will be favored for heaviest rainfall amounts in anomalously moist and strong 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 /03Z SUNDAY THROUGH THURSDAY/... Widespread IFR to VLIFR conditions will remain through the overnight as a saturated low layer remains under an inversion. Winds will be light and variable to calm overnight. Weak high pressure moves southeast of the area overnight as a wave of low pressure passes to the south. A large low pressure system moves from the lower Mississippi Valley into the Ohio Valley during Sunday. Conditions begin to improve around 14Z, with MVFR conditions expected around 16Z. Timing is uncertain at this time, and there is a chance IFR condition remain into Sunday afternoon. With the approach of the low, rain becomes likely by 22Z. Winds become easterly, 5 to 10 KT Sunday morning, and increase through the day, to near 15 KT with gusts around 20 KT by the end of the forecast period. There is a chance the low approaches more slowly, then rain and gusty winds would be delayed. .OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... .Sunday night...IFR in rain and fog. At KSWF light to moderate sleet likely toward 10Z. E-NE wind 20-30 KT G35-45 KT. .Monday-Monday Night...IFR in rain and fog. LLWS. Rain and sleet at KSWF. E-NE wind 25-35 KT G40-50KT, occasional higher gusts 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... Seas on the outer ocean water south of Montauk Point were running around 4 feet with a long period southeasterly swell. Made minor adjustments to the ocean seas for overnight. Dense fog remains across the forecast waters overnight, and a dense fog advisory remains in effect until 15Z. An intensifying storm moving up the coast Monday into Monday night will bring storm force gusts to all waters late Sunday night into Monday night. Easterly wind gusts 50-60 kt are expected mainly daytime Mon into Mon evening on the ocean, and beginning a little bit later Mon morning on the remaining waters. Strongest winds will be on the ocean, there is even a low prob of a brief period of hurricane force gusts (65+ kt) per 18Z NAM, which predicts 950-975 mb winds that strong and a well- mixed low- level. Max seas could peak at 20-22 ft on the ocean, 9-12 ft from Orient Point east, and 8-9 ft on central Long Island Sound, per combo of WaveWatch/NWPS guidance and wind/wave climatology. 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 bay and beachfront communities of LI with the Monday evening high tide. The moderate coastal flood potential will increase if the slower coastal low movement (stronger ene winds Mon eve) comes to fruition...with even a low potential for major flood thresholds to be reached in the most vulnerable communities such as Lindenhurst and Freeport. A coastal flood watch has been issued to address this moderate flood threat. Minor coastal flooding could linger for the southern and eastern bay areas for the Tuesday morning high tide cycle as well. 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...Dense Fog Advisory until 10 AM EST Sunday for CTZ005>012. High Wind Watch from late Sunday night through late Monday night for CTZ009>012. NY...Dense Fog Advisory until 10 AM EST Sunday for NYZ067>075- 078>081-176>179. 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...Dense Fog Advisory until 10 AM EST Sunday for NJZ002-004-006- 103>108. High Wind Watch from late Sunday night through late Monday night for NJZ006-106-108. MARINE...Dense Fog Advisory until 10 AM EST Sunday for ANZ330-335-338- 340-345-350-353-355. Storm Warning from 1 AM Monday to 1 AM EST Tuesday for ANZ330- 335-338-340-345-350-353-355. && $$ SYNOPSIS...BC/NV NEAR TERM...BC/MET/NV SHORT TERM...NV LONG TERM...BC AVIATION...MET MARINE...BC/MET/NV HYDROLOGY...NV TIDES/COASTAL FLOODING...

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