Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 231001 AFDOKX Area Forecast Discussion National Weather Service New York NY 601 AM EDT SAT JUL 23 2016 .SYNOPSIS... High pressure strengthens over the Tennessee Valley today. A weak cold front will pass through the region tonight, and then that high builds east on Sunday. A weak cold front approaches the area Monday and crosses Monday night. High pressure returns for mid to late week. A series of weak cold fronts may affect the region heading into the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Morning forecast on track. Will update hourly grids based on latest surface obs and satellite trends. High pressure over the TN Valley will impact the region today with hot and humid conditions. Meanwhile, a weak cold front approaches from the north during the day. The day will start off with dewpoints in the 60s to around 70. Weak surface trough passes through the region this morning, and then winds shift to a W-NW flow by early afternoon. A hot airmass builds into the region with highs generally in the low to mid 90s for much of the CWA and in the upper 90s to near 100 for NYC and urbanized portions of NE NJ. This warmer air could even spread into western portions of Long Island, where highs could top off in the mid to upper 90s. In addition, W-NW winds increasing to 10-20 MPH with gusts up to 25 MPH has the potential for strong mixing and will have an effect on the surface dewpoints. Current models suggest dewpoints falling into the low 60s by afternoon, there is the potential for dewpoints to fall into the mid and upper 50s for NYC/NE NJ. Heat Advisory remains in effect for NYC, Hudson, eastern Essex and eastern Union counties. For NYC, whose criteria for a Heat Advisory is 2 consecutive days of a Heat Index of 95 degrees or higher, Heat Advisory conditions will be met, as heat indices will be in the upper 90s. For NJ, think the heat index will come close to 100, especially early in the afternoon. Will keep Heat Advisory as-is. Have some questions about the humidity levels this afternoon with increasing W-NW winds and dewpoints mixing out. Could be less humid, but hotter, given the dryer conditions. With rough seas on the ocean this morning, and winds shifting from a S-SW flow to a W-NW flow this afternoon, can expect rough conditions on the waters. There is a borderline moderate to high risk for rip current development at Atlantic beaches this morning...falling to moderate this afternoon as southerly swells gradually abate. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... Weak cold front passes through the region tonight. Not expecting many impacts from its passage, but temperatures slightly cool off on Sunday as high pressure over the TN Valley continues to build east. Highs will top off in the upper 80s to low 90s for much of the CWA, and in the low to mid 90s for NYC/NE NJ. With surface dewpoints in the upper 50s to low 60s, can expect a heat index generally in the low to mid 90s. It is possible for the heat index in NYC to be under 95, and a Heat Advisory may not be needed for Sunday. With a weak flow over the region, conditions are ripe for the development of afternoon sea breezes. Have to monitor potential for Ambrose Jet and locally stronger onshore winds for coastal portions of NYC. High pressure moves offshore Sunday evening. Resulting S-SW flow behind the high will usher a very warm and humid airmass into the region Sunday night. Lows will only drop into the mid and upper 70s for NYC and surrounding areas, and will be in the upper 60s to low 70s elsewhere. Some outlying spots could drop into the low 60s. Patchy fog is possible as well outside of NYC. && .LONG TERM /MONDAY THROUGH FRIDAY/... A heat ridge will continue to dominate the the southern 1/2 to 2/3rd`s of the country to start the week...with the tri-state region lying on the northern periphery. Models in fairly good agreement with a vigorous PAC shortwave over the NW US this morning...phasing with northern stream Sun/Mon...and eventually forming a closed low over Northern Ontario/Quebec for mid/late next week. An associated shearing shortwave trough approaches the Northeast US on Monday...and swings through the region Monday night. At the surface...a resultant weak cold front approaches Monday and crosses Monday night. Ahead of it...with deep mixing and 850 temps of 20-21c...temps should be able to climb into the mid to upper 90s. The amount of filtering of sunshine is the main uncertainty due to high/mid clouds from upstream convection. Moisture pooling dewpoints into the upper 60s/lower 70s will have potential for heat indices of 100 to 104 for NYC metro/NE NJ/Lower Hud/and interior southern CT. There is a low potential for 105 heat indices. In terms of convection...with building instability and approaching shortwave energy Monday aft/eve...potential for tstm development along thermal/pre-frontal trough. Some uncertainty on strength of shortwave energy...and how it times with peak heating/instability this far out. That interaction will determine convective coverage and severity, and will be refined as time period nears. Cold frontal passage expected Monday night...with any shower/tstms activity translating eastward and offshore. High pressure builds into the area on Tuesday, ushering in only slightly cooler but more so a drier airmass. Highs on Tuesday will be in the lower to mid 90s, and with surface dewpoints in the 60s, with heat indices in the mid to upper 90s. Region will lie between southern heat ridge and earlier mentioned Ontario/Quebec upper low during the mid to late week period...which will likely have weak shortwaves rotating through the NE. Very warm conditions will continue for the mid to late week...with high generally about 5 degrees above seasonable...well into the 80s to lower 90s. As moisture slowly increases...potential for aft/eve tstm activity may increase as the week progresses as well. && .AVIATION /10Z SATURDAY THROUGH WEDNESDAY/... A weak cold front moves through towards daybreak. VFR conditions expected through the TAF period. There is a low chance for some patchy fog and MVFR vsbys early this morning outside the NY metro. WNW flow is likely this afternoon with gusts 20-25KT. Winds generally left of 310 mag for NYC/NJ metro terminals...but could waver just to the right in the afternoon for KLGA. Coastal sea breeze development is not expected. Winds and gusts diminish in the evening...with light nw winds tonight. .OUTLOOK FOR 06Z SATURDAY THROUGH WEDNESDAY... .late tonight through SUN NGT...VFR. .MON...Mainly VFR, except MVFR or lower possible in scattered late day/evening thunderstorms. .TUE and WED...VFR. && .MARINE... With conditions falling below SCA criteria on the ocean waters east of Fire Island Inlet, will go ahead and cancel the SCA that was in effect until 6 AM. Winds currently from the W-SW at 5-10 KT, and will become W-NW at 10-15 KT with gusts up to 20 KT by early afternoon. Winds diminish and may become LGT/VRB tonight. Afternoon sea breezes likely on Sunday, and have to monitor potential for locally strong onshore flow from Sandy Hook to Fire Island Inlet Sunday afternoon. For now, believe gusts should stay below SCA criteria. Sub-SCA conditions continue into Sunday night, but there is the potential for the development of fog. Potential for marginal sca conditions on Monday Aft/Eve for ocean and south coastal nearshore waters with increasing s/sw flow ahead of a cold front. Otherwise...sub sca conditions for mid week as high pressure builds in. && .FIRE WEATHER... There is the potential for minimum RH values of 25-30 percent along with W-NW winds gusting as high as 25 MPH this afternoon for NYC and coastal portions of NE NJ. && .HYDROLOGY... Dry conditions are expected through Sunday night. Potential for scattered showers and thunderstorms Monday afternoon into Monday Night, producing heavy downpours. There is potential for sct diurnal convection late week into weekend. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory until 7 PM EDT this evening for NYZ072>075-176- 178. NJ...Heat Advisory until 7 PM EDT this evening for NJZ006-106-108. MARINE...None. && $$ SYNOPSIS...MPS/NV NEAR TERM...MPS SHORT TERM...MPS LONG TERM...NV AVIATION...NV MARINE...MPS/NV FIRE WEATHER... 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