Area Forecast Discussion
Issued by NWS Upton, NY

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375 FXUS61 KOKX 150603 AFDOKX Area Forecast Discussion National Weather Service New York NY 203 AM EDT Tue Oct 15 2019 .SYNOPSIS... A dry cold frontal passes east overnight, followed by building high pressure through Tuesday. A frontal system will approach on Wednesday, with a rapidly intensifying coastal low tracking just southeast of the area Wednesday Night, and into the Canadian Maritimes Thursday into Thursday Night. High pressure builds in for next weekend. Another frontal system approaches for early next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Cold front extends across the east end, and passes east overnight. High pressure over the Ohio Valley then builds east through the night. Patchy fog over astern LI should scour out as the front passes east and a light north wind develops. Otherwise, mainly clear skies are anticipated. Overnight lows will be right around normal, generally in the 40s, except around 50 for the NYC metro. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... Shortwave ridging between one departing upper low over eastern Canada and an amplifying trough over the upper Midwest into the Great Lakes, will result in dry, seasonably cool conditions. Any clouds will be on the increase late Tuesday night as a frontal system approaches from the west. A light northerly flow in the morning will become onshore in the afternoon as surface high pressure works offshore. Highs on Tuesday will top out in the lower 60s. Lows Tuesday night will likely vary considerably due to good radiational cooling, from the lower 50s in metro NY, to the mid 30s to lower 40s elsewhere. With a light onshore flow and increasing low-level moisture, fog may be a possibility as well as frost. Guidance still showing dew point depressions significant enough to leave mention of fog out at this time. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Main story during this period will be a strong frontal system/developing coastal low affecting the region late Wednesday into Thursday. Main features will be a strongly amplifying northern stream shortwave digging through the US/Canada border of the Rockies this afternoon. This feature will develop a closed upper low that slides into the upper Great lakes Tue/Tue Night, then phases with the southern stream Wednesday morning. The phasing and deepening closed low will approach the region Wednesday, and then pivoting through the area Wed Night into Thu morning and up the New England coast into the Canadian maritimes Thu afternoon thru Thu Night. At the surface, low pressure associated with the northern stream closed low will track east through the Great lakes Tue into Wed, with its associated strong cold front pushing towards the region late Wednesday. At the same time, phasing jet energy will begin to intensify a southern wave of low pressure tracking ne ahead of the front off the Mid-Atlantic coast; tracking just SE of LI Wed night. This will become the primary intense low pressure by Thursday morning as it tracks up the New England coast. There is good general model agreement in the above scenario, but still some spread on intensity of the developing coastal low as it tracks se of LI and into New England, and to a lesser extent spread in how close or over the area the low tracks. The sensitivity of this appear to be with evolution of a Central PAC closed low, and downstream amplification of west coast ridging and northern stream shortwave, and then the eventual phasing with southern stream. The main implication for our area would be modest, in terms of amount/axis of rain and strength of winds ahead and behind system. This should come into better focus over the next 24-48 hrs. Strong deep layer forcing with this system and a deep subtropical PAC and Gulf moisture connection (+1 1/2-2 std PWATS) point towards a heavy rain event late Wed through Wed Night. Strong forcing, closed low/vort energy moving through aloft, and weak surface instability point to potential for some deeper convection and embedded thunder. This brings likelihood for 1 to 2 inches of rain, with locally 2-4" inches of rain possible. Rain should quickly taper off late Wed night as trough axis pivots east. Deep cyclonic flow on Thursday will result in considerable cloud cover with scattered showers/sprinkles, particularly interior. Can`t even rule out a wet snow flake or two across the far NW hills in any heavier showers as cold pool moves through aloft and coolest airmass of the season works in. In terms of winds, ahead of the low a period of E/SE winds 20 to 25 mph gusts 30-35 mph (peak winds 25-30 gusts to 40 mph possible across eastern LI) likely along the coastal plain Wed afternoon/evening. Then in the wake of low pressure W/NW winds of 20 to 30 mph and gusts to 40 to 45 mph likely late Wed Night into Thursday. There is potential for wind advisory 30-35 mph and gusts to 50 mph if stronger low development verifies. Windy conditions will continue into Thursday Night, although gust potential likely decreases with decreased instability. Cyclonic flow will be slow to relent through the day Friday. NW winds will be weakening, but still a a breezy day. Another below seasonable day with sct-bkn afternoon strato-cu. Then a gradual moderation to seasonable and then above seasonable temps and fair weather this weekend as upper ridging build in and high pressure builds to the south of the region. Next chance of rain looks to be some time early next week, as another deep trough develops over the central US, with an increasingly moist and active flow deep SW flow developing into the Eastern US. indication are a slow moving frontal system or systems approaching for Monday/Tuesday. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... High pressure builds in through the TAF period. VFR conditions are expected for all terminals. For NYC terminals, winds will be relatively higher going into Tue AM with N-NW flow of 10-15 kt decreasing to near 10 kt. Winds then eventually shift to more of a SW direction at 5-10 kt Tue afternoon with sea breeze circulations developing. Otherwise, rest of terminals have an initial NW wind of 5-10 kts that will eventually become more SW during Tue afternoon at nearly the same wind speed with developing sea breeze for coastal terminals. .OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY... .Late Tuesday night...VFR. Winds become more SE. .Wednesday...Rain developing. Conds quickly lowering to IFR late afternoon/evening, lingering past midnight at KGON. SE winds G25kt. LLWS also possible along the coast late afternoon/evening, mainly at KISP/KGON. .Thursday...VFR. NW winds G25-35kt. .Friday...VFR. NW winds G20-25kt mainly AM. .Saturday...VFR. && .MARINE... The pressure gradient remains relatively weak during the short term through Tuesday night. Conditions are expected to remain below SCA across all local waters. SE winds increase across the waters on Wed ahead of an approaching cold front and developing low pressure. SCA conditions expected on all waters by early Wed afternoon into Wed evening. A brief period of SE gales likely on the ocean waters east of Moriches inlet as the low approaches, and possible for the rest of the ocean waters and the eastern Sound/bays. Winds expected to shift to the NW Wed evening, with W-NW gales likely on the ocean waters late Wed night, and on all waters for Thursday. Gale conditions should fall to SCA Thu Eve/night, with SCA wind gusts likely subsiding Friday morning into afternoon. Ocean seas will rapidly build Wed aft/eve, but should fall below SCA Fri afternoon as winds weaken as they will be wind wave dominant. && .HYDROLOGY... A significant rainfall of 1-2 inches is likely Wednesday afternoon into Wednesday night, with localized swaths of 2-4 inches possible. The bulk of the rainfall is expected in a 6-9 hr period late Wednesday afternoon through Wednesday evening. Urban, poor drainage, and low lying flooding is expected. There is a low probability of flash flooding along a few of the fast responding small rivers and streams in NE NJ and the Lower Hudson Valley if the higher rainfall amounts are realized. Additionally, localized flash flooding will also be an issue for coastal roads if heaviest rain coincides with the Wed Night high tides. && .TIDES/COASTAL FLOODING... Tidal departures of generally 2 to 2 1/2 ft above astronomical are needed for minor flooding during the times of high tide late Wed Eve into Wed night. There is quite a bit of spread in the ensemble guidance, partly due to some differences in the potential strength of low pressure wind fields, and equally so due to timing of a wind shift from E-SE winds to NW as low pressure moves by. At this point, model consensus would indicate potential for widespread minor coastal flooding, with a low probability for localized moderate impacts where wave action combines with elevated water levels. If the heaviest rain coincides with the Wed night high tide, more widespread flooding could be experienced than would normally be expected. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO35 (162.55 MHz) remains off the air. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...NV/DW NEAR TERM...NV/DW/PW SHORT TERM...DW LONG TERM...NV AVIATION...JM MARINE...NV/DW/PW HYDROLOGY...NV/DW TIDES/COASTAL FLOODING... EQUIPMENT...

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