Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 201942 AFDOKX Area Forecast Discussion National Weather Service New York NY 342 PM EDT Fri Jul 20 2018 .SYNOPSIS... High pressure will retreat to the northeast through Saturday while a small coastal storm works up the Eastern seaboard, affecting the region this weekend. A frontal boundary will then remain nearby through mid week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Ridging aloft and centered over/just E of New England will remain in place as a negatively tilted upper trough digs southeast from the upper Midwest, the latter of which will help steer a small coastal storm now taking shape off the Carolina coast on Saturday. Expect another day of mostly sunny skies, seasonable temperatures and low humidity. Southeast winds will increase to around 10 kt this afternoon, but a bit stronger along the coast due to the sea breeze. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Upper trough over the Midwest closes off an upper low as it continues to dig southeast, tracking into the Ohio Valley on Saturday. Low pressure located along the Mid Atlantic coast Saturday morning will work northward at it gets caught up in the deep-layered southerly flow ahead of the trough. It never quite phases and there appear to be issues with convective feedback (due to parameterization) with the non-CAM models, as well as large timing differences. The 00Z GFS is as fast as the NAM-3km, while the GEFS is more in line with the slower GGEM, ECMWF, EPS, and NAM-12km. Preference at this time was to trend slower this run, thus have decreased rain chances Saturday afternoon. The bulk of the rain and strong easterly flow will be featured Saturday night. Overnight lows will be near seasonable levels, while highs on Saturday will only be in the 70s due to a strengthening easterly flow and increasing mid and upper level clouds. The rip current risk will increase through the day Saturday, with a moderate to possibly high risk in the afternoon. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... A highly anomalous pattern setting up for the weekend into mid next week, with a deep upper low with heights 2-4 standard deviations below normal sinking south through the Ohio valley this weekend and into the deep South early next week. Meanwhile, western Atlantic ridging will remain strong, beginning to gradually build westward early to mid next week. The region will be in between both features, with a deep-layer southerly flow and maritime tropical regime in place. Feature of concern continues to be a developing mid level shortwave trough along the SE coast today being picked up and phasing with the larger upper low as it pivots NNW toward the region on Sat. At the surface, good agreement with an intensifying frontal low developing along the SE US coast Fri night, tracking up the coast Saturday towards the Delmarva, and then a marked operational and ensemble (GEFS/EPS) model trend over the last 12 hrs of low pressure taking a NNW track up through NJ/E PA Sat night/Sunday morning. With this said, there is still at least a 100-150 mile spread in track of low pressure from just NW of NY metro into E. Central PA/NY, plus a 6-hr timing difference. These types of differences are to be expected with the convective activity expected to be associated with the low, which will have to be refined over the next 24 hours. With this type of track, main hazards appear to be heavy rain, potential for a few low topped strong to possibly severe thunderstorms with warm frontal passage and in the warm conveyor belt, and potential for a period of moderately strong gradient winds late Sat into Sunday morning. In terms of heavy rain, a quick hitting 1-2 inch rainfall still looks likely, with it becoming more likely that the bulk of heavier 2-4+ rainfall will occur to our west, across PA. The one caveat will be the position of the warm conveyor belt rains and convection, which would have the potential to bring some training of thunderstorms across LI/CT and potential for locally 2+ inches of rain. There is still quite a bit of uncertainty as to exactly where that axis will set up. In terms of a severe thunderstorm threat, a low potential continues for isolated strong/damaging wind gusts or a weak tornado, in a high shear/low CAPE environment with 40-50 kt veering 950 hPa LLJ as the warm front makes its passage. As mentioned above, there is still uncertainty on timing/placement/weakening rate of core of an anomalously strong S LLJ of 50-60 kt at 950 hPa. But with moist adiabatic lapse rates in wake of warm frontal passage, potential exists to transport strong to damaging winds down to the surface in any isolated stronger convection within the LLJ axis. Will have to monitor evolution of the LLJ/WCB over the next 24 hrs, as well as depiction of convection in the CAM`s to get a better sense of where this threat may lie. Otherwise, moderately strong easterly winds gusts of 30-40 mph are likely along the coast ahead of the low Sat Night (low prob of 40+ mph), and then veering to the S-SE early Sun morning in the wake of warm fropa. The S-SE wind threat early Sun morning looks primarily to be over E LI/SE CT with the LLJ. The remainder of the period continues unsettled in this tropical maritime flow regime, with deep troughing to the west, and Atlantic ridging gradually building westward. Shower and isolated thunderstorm activity appears likely Sun night into Monday as a weak shortwave rounds the closed low to the west and the weakening warm conveyor belt retrogrades west. It seems as the most widespread shower axis pushes west of the Hudson River and possibly farther west for mid-week as Atlantic high builds westward, but likely pushes back across the region for late week/weekend. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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High pressure gradually shifts towards the Canadian Maritimes tonight and early Saturday. Low pressure will approach from the south and pass west of the NYC terminals Saturday night. High confidence of heavy rain and gusty winds Saturday night with LLWS likely late. VFR through mid-afternoon Saturday then chance of MVFR arriving Saturday late afternoon in scattered showers. Winds SE around 10-15 kt with a few higher gusts near the coast. Winds diminish tonight, becoming more easterly by 12z Saturday. Gust E-SE winds 15-25kt developing at the coast around 20z Saturday. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: No unscheduled amendments expected tonight. Timing of showers and lowering ceilings Saturday afternoon may be off by 1 or 2 hours. KLGA TAF Comments: No unscheduled amendments expected tonight. Timing of showers and lowering ceilings Saturday afternoon may be off by 1 or 2 hours. KEWR TAF Comments: No unscheduled amendments expected tonight. Timing of showers and lowering ceilings Saturday afternoon may be off by 1 or 2 hours. KTEB TAF Comments: No unscheduled amendments expected tonight. Timing of showers and lowering ceilings Saturday afternoon may be off by 1 or 2 hours. KHPN TAF Comments: No unscheduled amendments expected tonight. Timing of showers and lowering ceilings Saturday afternoon may be off by 1 or 2 hours. KISP TAF Comments: No unscheduled amendments expected tonight. Timing of showers and lowering ceilings Saturday afternoon may be off by 1 or 2 hours. .OUTLOOK FOR 21Z SATURDAY THROUGH WEDNESDAY... .Saturday...VFR. Low chance of MVFR in scattered showers late. Gusty E gusts 20-25 kt late day. .Sat night...Rain, heavy at times. MVFR/IFR develop in the evening. E-SE gusts 25-30 kt. CHC gusts to 35 kt at coastal terminals. LLWS likely late night. Isolated TSTMs. .Sunday...MVFR/VFR with periods of SHRA/TSTMs. S gusts 20-25 kt. .Sunday night...Mostly MVFR with a chance of IFR in SHRA and isolated TSTMs. S gusts 20-25 kt. .Monday-Wednesday...MVFR/VFR with periods of SHRA and a chance of TSTMs. S gusts 20-25 kt.
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&& .MARINE... High pressure lifts northeast through Saturday which will allow for a SE flow into this evening. Winds then back to the E on Saturday as low pressure works north along the eastern seaboard. As a result, easterly winds will strengthen through the day, with SCA conditions possibly developing in the afternoon. Gale conditions appear likely on the ocean waters late Sat into Sun morning, and potentially over all the nearshore waters, with a tight pressure gradient driving E-SE winds ahead of the low as it tracks just to the west. This will likely result in rough conditions on the ocean waters, peaking in the 8-12 ft range. Generally Sub-SCA winds are expected thereafter Sun afternoon into next week, but southerly SCA swells will be slow to subside below 5 ft early next week. && .HYDROLOGY... Rainfall of 1-2 inches is likely from late Saturday into Sunday morning. Locally higher amounts are possible, especially in any thunderstorms that develop. Minor urban and poor drainage flooding looks to be the main threat. A localized threat for flash flooding exists with any training convection and also if heavy rain coincides with high tide levels approaching minor flood levels Sunday morning. Additionally, if high end of rainfall amounts is realized across the quick responding NE NJ and Lower Hudson Valley river basins, minor flooding would be possible as well. Dependent on the axis of shower and thunderstorm activity early and more-so late next week, potential exist for at least minor urban, poor drainage and small stream flooding issues across the Lower Hudson Valley, NE NJ, and possibly into the NYC metro. && .TIDES/COASTAL FLOODING... There is a slight (10-20%) chance that locations in/around the NY Bight, including the shores of Staten Island and the back bays of southern NYC and southern Nassau, could experience minor coastal flooding with the high tide cycle early Sunday morning, especially if strongest winds coincide with the high tide. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Gale Watch from Saturday evening through Sunday morning for ANZ330-335-338-340-345-350-353-355. && $$ SYNOPSIS...NV/DW NEAR TERM...Goodman/DW SHORT TERM...DW LONG TERM...NV AVIATION...IRD MARINE...Goodman/NV/DW HYDROLOGY...NV/DW TIDES/COASTAL FLOODING... EQUIPMENT...

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