Area Forecast Discussion
Issued by NWS Upton, NY

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881 FXUS61 KOKX 182328 AFDOKX Area Forecast Discussion National Weather Service New York NY 628 PM EST Sat Nov 18 2017 .SYNOPSIS... As developing low pressure approaches from the west, its associated warm front will lift to the north this evening, and then an associated strong cold front will move across Sunday morning as the strong low passes to the north. High pressure will pass to the south Monday and Tuesday, followed by a cold front on Wednesday. High pressure will build late week. Low pressure will then move across on Saturday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Rain with the warm front has spread across much of the area this evening. S winds along the coast are gradually increasing, and think the strongest S-SW winds will occur after warm fropa overnight as boundary layer temps rise and low level mixing improves. Models continue to indicate H9 winds in the 50-60 kt range, with a well-mixed boundary layer and also bands of moderate to locally heavy showers capable of transporting most of this momentum to the surface. High wind warnings were issued for Suffolk and coastal SE CT as a result, and wind advisories expanded westward to include all coastal sections including NYC. Strongest winds should occur overnight and especially near/across the forks of Long Island, though NAM timing is a little sooner and its LLJ a little stronger than that of the global models (up to 70 kt). Delayed the onset slightly to account for lighter winds this evening. Instability with bands of showers overnight will be limited to the low to mid levels, with an H6 inversion limiting deeper/greater instability that would have otherwise led to thunder.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Cold front will be moving across in two shots, the first marking arrival of a dry slot and departure of the S-SW low level jet, the second marking the arrival of strong W-NW winds after passage of a potent, negatively-tilted shortwave trough along. There could be a brief lull in winds between these two features, but then W-NW winds likely to gust just over 45 mph with passage of the second trough (with NAM indicating narrow band of showers with the front), and then during the late morning and afternoon via a tight pressure gradient and H8 winds up to 40-45 kt. Stronger winds should hang on a few hrs longer into the daytime than model forecasts indicate, and NAM also indicates stronger H8 winds arriving in the late afternoon after another mid level shortwave passage; think winds will however start to gradually diminish by that point, so while gusty NW winds will continue into Sunday night, have not extended the advisory into Sunday night. After morning highs in the 50s, temps should gradually fall in the afternoon, back into the 40s by late afternoon, then into the 20s and 30s tonight. A few lake effect snow showers may make it into the area late Sunday night especially just NW of NYC. && .LONG TERM /MONDAY THROUGH SATURDAY/... Aloft, models agree early in the period as initial shortwave passes east/northeast. Downstream shortwave will then make fast eastward progress. Here is where some differences arise. Northern stream potent shortwave tracks across the Great Lakes region as it lifts northeast, with most of the energy and associated dynamics lifting well to our north Wednesday. Southern stream trough lags a bit as it moves across the Gulf states. By late Wednesday into Thursday, operational GFS seems to be a deep/strong outlier with regard to closed low around the Gulf states as the trough makes eastward progress. This upper trough weakens over the western Atlantic Thursday, with next shortwave in the northern stream moving eastward toward the northeast by next weekend. At the sfc, high pressure passes to the south Monday and Tuesday. Gusty NW flow will back around the SW as the high tracks east. Thereafter, a cold front passes Wednesday. This front is associated with northern stream shortwave. This looks like the best chance for measurable precipitation, late Tuesday night into Wednesday, chance pops. Waves of low pressure likely develop along the front well to our south in the Wednesday night/Thursday time frame. Again, GFS appears to be an outlier with wave of low pressure developing and passing close enough for measurable precip Thursday. Otherwise, model consensus suggest any precip remains to our southeast as ridge builds to the NW and waves remain far enough to the southeast. Will maintain a dry forecast as a result, leaning toward consensus. However, this will need to be watched. Dry through Friday before the next chance for precip arrives with the shortwave, clipper low Saturday. As for temperatures Monday-Saturday, followed a model/mos blend. Below normal temperatures Monday will warm to slightly above normal Tuesday as WAA occurs behind the high. Behind a cold front Wednesday, normal temps likely fall to below normal Thursday and Friday before rebounding yet again in WAA ahead of the clipper low Saturday. && .AVIATION /00Z SATURDAY THROUGH THURSDAY/...
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A strong low pressure system approaches tonight sending a warm front north of the terminals. A cold front follows early Sunday morning with high pressure building behind it through Sunday evening. S flow has temporarily weakened this evening, but the expectation is for the winds to increase overnight as the warm front moves north. Gusts will return, initially 20-30 KT just after midnight, increasing to 30-40 KT towards day break. Some eastern terminals may see peak gusts 45-50 KT. LLWS is also forecast across eastern Long Island and southeast Connecticut as the cold front moves through. S-SW winds shift to the W-WNW Sunday morning with gusts frequently 35-40 KT during the day. The gusts will begin to weaken late in the afternoon and early in the evening. Mainly VFR conditions to start this evening with conditions gradually becoming MVFR with steadier showers moving in overnight. There may also be some brief localized IFR. Conditions will improve to VFR Sunday morning behind the cold front. .OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... .Monday...VFR. W-NW winds G20-30KT. Gusts diminish gradually at night. .Tuesday...Mainly VFR. MVFR possible late Tuesday night in showers. SW winds G15-20KT. .Wednesday...MVFR possible with showers during the day. VFR at night. W-NW winds G15-20KT. .Thursday...VFR.
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&& .MARINE...
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S-SW winds will increase to gale force later this evening, then a strong low level jet with only a weak inversion at best should allow storm force gusts to occur on the eastern ocean/sound/bays, where a storm warning has been issued. Farther west, winds should still gust to 35-45 kt, and a gale warning remains in effect. After a cold frontal passage Sunday morning, W-NW winds should gust to 40-45 kt through the day, and fall below gale force on the non-ocean waters after midnight. Gusty NW/W flow Monday will back around the SW Monday night and Tuesday as high pressure passes to our south, then east. These SW winds eventually shift around the N/NW behind a cold front Wednesday. Northerly winds persist Wednesday night and Thursday. As for sea forecasts, rough conditions persist in the Monday and Tuesday time frame due to strong winds/tight pressure gradient. Nearshore Wave Prediction System looked quite reasonable and was followed. For Wednesday and Thursday, had to knock down sea forecasts from Wave Watch III as GFS appears to be an outlier with regard to a wave of low pressure that approaches the waters from the south/southeast.
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&& .HYDROLOGY... Rain with a warm frontal passage tonight, and then with bands of moderate to locally heavy showers with a strong cold frontal passage late tonight into Sunday morning, should cause no more than local nuisance impacts. Total rainfall is expected to range between 1/2 to 1 inch, highest NW of NYC. && .TIDES/COASTAL FLOODING...
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Storm surge guidance for Sunday morning high tide may to be on the low side given the strength of southerly winds expected tonight into Sunday morning ahead of a cold front. But typically, S/SW winds are not conducive to building surge. There is a low probability of a surge of 1-2 ft Sunday morning. If these surge levels develop, minor coastal impacts in a strong SW/W flow would be felt mainly across eastern portions of the Great South Bay into Moriches Bay. Elsewhere any impacts would be brief and localized. Statement issued to address this potential.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...High Wind Warning from midnight tonight to noon EST Sunday for CTZ011-012. Wind Advisory from 7 AM to 6 PM EST Sunday for CTZ005-006. Wind Advisory from midnight tonight to 6 PM EST Sunday for CTZ007>010. NY...High Wind Warning from midnight tonight to noon EST Sunday for NYZ078>081. Wind Advisory from 7 AM to 6 PM EST Sunday for NYZ067>070. Wind Advisory from midnight tonight to 6 PM EST Sunday for NYZ071>075-176>179. NJ...Wind Advisory from 7 AM to 6 PM EST Sunday for NJZ002-004- 103>108. Wind Advisory from midnight tonight to 6 PM EST Sunday for NJZ006. MARINE...Storm Warning until noon EST Sunday for ANZ330-340-345-350-353. Gale Warning until 6 AM EST Monday for ANZ335-338-355.
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&& $$ SYNOPSIS...Goodman/PW NEAR TERM...Goodman/PW SHORT TERM...Goodman LONG TERM...PW AVIATION...DS MARINE...Goodman/PW HYDROLOGY...Goodman/PW TIDES/COASTAL FLOODING...

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