-- Discussion containing changed information from previous version are highlighted. --
771
FXUS61 KOKX 040841
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
441 AM EDT Thu Jul 4 2024

.SYNOPSIS...
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A weak cold front moves towards the area today and stalls near
the area tonight into Friday morning. This front lifts back
north Friday, with a slow moving frontal system pushing through
the region Friday Night into Saturday Night. The front stalls
just southeast of the area Sunday into Monday as weak high
pressure builds into the area. The front may then lift back to
the north Monday night into Tuesday ahead of another frontal
system working east across the Great Lakes and Ohio Valley
states.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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General agreement on broad upper troughing across southeastern
Canada today into tonight, while a closed low develops over the
northern plains and slides east into the Great Lakes. This will
place the region on the southern edge of an active (convectively
induced vorts and enhanced weak shortwaves) southwesterly upper
flow.

At the surface, a weak cold front/pre-frontal trough approaches
today and then settles over the region tonight. Seasonably warm
and very humid conditions with continued WAA WSW flow aloft
today (lower 80s coast to mid to upper 80s NYC metro and areas
N&W). 90 to 95 degrees heat indices likely for NE NJ this
afternoon.

Weak shortwave/vort energy moving through the upper flow should be
trigger for isolated to scattered slow moving tsra/downpour
development in vicinity of weak pre-frontal trough/cold front to
the west and possible isolated development along well inland
moving sea breeze boundary in a marginally unstable and sub-
tropical environment (2"+ PWATS) this aft/eve.

Models in better agreement with a weak but distinct convectively
enhanced shortwave over the Mid Mississippi River Valley this
morning, approaching the region this evening. Models have also
consistently trended upwards towards building marginal instability
and deep layer shear for areas west of the Hudson R thru PA this
aft/eve ahead of approaching shortwave. This has increased
confidence in scattered tstm and heavy downpour development across
PA working into areas w of the Hudson R this aft/eve. Can`t rule out
an isolated strong storm across this area. Interestingly CAMs
are less bullish on convective coverage than 12 to 24 hrs ago,
perhaps due to a bit slower shortwave approach, outside of peak
aft heating. SPC HREF 3"/3hr of 10 percent is currently
centered over the LoHud and SE PA, signaling an isolated threat
for flash flooding from slow moving and deeper convection.

With seabreeze (marine layer) working N&W of NYC/NJ metro this
aft/eve, convection should become elevated and weaken as it
moves to the coast. With shortwave support moving east and sub-
tropical environment, threat for a few downpours and embedded
elevated tstms could translate east across NYC, CT and LI
tonight. The weak frontal boundary appears to sink just south of
the region late tonight as shortwave energy moves east,
bringing convection threat to an end. Otherwise, warm and muggy
conditions tonight, with potential for nocturnal stratus/fog
development in moist and weak flow environment.
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&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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Broad upper troughing across southeastern Canada retreats
northward Friday into Saturday, with the closed low over the
Great Lakes Friday shearing into Ontario/Quebec on Saturday. The
weak shortwave moves east of the region Friday AM, with another
weak shortwave approaching Fri eve.

At the surface, its appears the weak cold front sinks south of
the region by daybreak Fri, but then lifts back north as a warm
front Fri PM, aided by afternoon seabreeze development.
Subsidence and mid- level drying in the wake of the departing
shortwave should allow for a window for good heating after
morning stratus/fog dissipates. This should allow for very warm
and humid conditions (lower to mid 80s coast, to upper 80s to
around 90 for NE NJ and LoHud). Potential for iso to scattered
late aft/eve convection, mainly for areas N&W of NYC with
approach of next shortwave, and in vicinity of warm
front/seabreeze, in a marginally unstable and modestly sheared
environment. An isolated strong storm possible. Lack of focus
and stabilizing marine layer to the east across the coast should
limit shra/tsra activity thru Fri eve.

Increasing threat for heavy downpours and embedded tstm
developing and sliding w to e across the entire area Fri Night
thru Sat AM with strengthening mid/upper support ahead of
shearing closed low to the west, and strengthening low-level jet
ahead of eastward moving pre-frontal trough advecting in an
increasingly sub-tropical (weak instability, deep moisture and
warm cloud layer, and 2"+ PWATS) environment.

Pre-frontal trough appears to stall over the area Sat, with
potential for scattered afternoon convection ahead/along
this Sat aft/eve. This appears to be the best chance of a few
strong to severe tstms, particularly NYC and points N&W, based
on mid- upper level support ahead of shearing shortwave trough
axis, moderate deep layer shear and marginal instability
environment. Activity should weaken in intensity as it
translates to the coast with waning instability and deepening
coastal stable layer Sat Eve.

GEFS initialized CSU MLP indicating a 5 to 15% probability of
excessive rainfall with this activity Saturday. Exact location
of the boundary will determine possible focus for training
convection and localized flash flood threat as flow parallels
the stalled boundary. More clarity on this part of the forecast
in the next 24 to 48 hrs.

Finally, very warm temps with an increasing humid airmass is
increasing the potential of heat advisory criteria being met for
NE NJ and possibly portions of the LoHud for the Friday-
Saturday period.
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&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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Not much change from what was inherited as hot and humid conditions
are likely to persist through the long term, featuring a longwave
trough over the Central US and a Western Atlantic ridge. The upper
air pattern gradually translates east during this time.

At the onset of the period, a weak cold front will pass just
southeast of the area early Sunday morning with high pressure
building in from the west into Monday. This should be a dry start to
the period, but will need to watch how far offshore the boundary
gets. Shortwave energy embedded within the longwave trough to the
west will then send a frontal system east across the Great Lakes and
Ohio Valley states Monday night into Tuesday.
This will bring increasing chance of convection Tuesday into
Wednesday.

A deep-layered SW flow during this time will maintain very warm
conditions across the area along with increasing humidity through
the middle of next week. Daytime highs during this time will
generally be in the mid and upper 80s away from the immediate coast,
along with some lower 90s across metro NJ. Lows will mainly be in
the upper 60s to lower 70s, warmest across the NYC metro. Max heat
indices at this time look to fall just short of 95. Largely stayed
close to national blended guidance for this update. Highs generally
fall below the 50th percentile and in some cases below the 25th
along the coast.
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&&

.AVIATION /08Z THURSDAY THROUGH MONDAY/...
Offshore high pressure will continue to give way to an
approaching surface trough that moves into the area late
Thursday.

This will be a mainly VFR forecast outside of any aft/eve
showers and thunderstorms. The best chance looks to be across
the Lower Hudson Valley and NYC terminals. There is some
uncertainty as to how quickly the activity will weaken as it
approaches the NYC terminals. For the time, only mention showers
after 00Z for the eastern terminals.

Chance of MVFR late Thursday night (after 06Z).

S-SW winds at less than 10 kt overnight will strengthen a bit
after 12Z at the coast with perhaps a few gusts into the teens.
However, there is less confidence of a southerly coastal jet
forming in the late aft/eve impacting the NYC terminals. If this
does happen, there could be a few gusts to around 20kt, mainly
at KJFK. Winds back to more southerly in the afternoon.

 ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Amendments will be likely for the timing of showers and
thunderstorms Thursday late afternoon and evening.

KEWR may for a time become 140-150 due to a seabreeze in the
afternoon.

OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY...

Friday and Saturday: MVFR or lower cond possible at times with
continued chance of showers/tstms.

Sunday and Monday: VFR.

Detailed information, including hourly TAF wind component
forecasts, can be found at: https:/www.weather.gov/zny/n90

&&

.MARINE...
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Prevailing sub-SCA conditions through Friday. However, marginal SCA
gusts possible this aft/eve at the entrance to NY Harbor and western
Great South Bay with coastal jet development. Ocean seas may
approach 5 ft in this area this eve.

Winds and seas expected to remain below SCA levels on Friday with
slightly weaker pressure gradient.

Better chance of SCA cond Fri Night into Sat Night on the ocean
as strengthening S flow increases to 15-20G25kt and seas build
to 4 to 6 ft. Potential for nearshore gusts to 25 kt as well.

High pressure building across the waters Sunday into Monday will
result in a weak flow and sub-SCA conditions.
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&&

.HYDROLOGY...
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Isolated slow moving thunderstorms with heavy downpours producing 1-
2"/hr rainfall rates are possible this aft/eve and Fri aft/eve,
mainly west of the Hudson River. Primary threat is for minor/poor
drainage flooding.

Approaching shortwave and slow moving frontal boundary crossing
Friday night into Saturday NIght will bring the potential for
localized 1-2"/hr rainfall rates with scattered heavy downpour
and embedded tstm threat across the entire area. With limited
instability for deep convection, primary threat will be for
minor urban/poor drainage flooding, but a localized flash flood
threat will exist in path of any training convection. Exact
location will be refined over the next 24 to 48 hours.
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&&

.TIDES/COASTAL FLOODING...
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There is a moderate to high risk for rip current development
along NYC/LI ocean beaches today and Friday with a combo of
building southerly wind wave and 2 to 3 ft E/SE swell. The high
risk is for W LI and NYC beaches this aft/eve due to enhanced
seabreeze formation and large tidal range, which is possible
once again Fri aft/eve.

More widespread threat of high risk of rip currents for all
NYC/LI ocean beaches possible on Saturday.
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&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None.
NY...High Risk for Rip Currents from noon EDT today through this evening
     for NYZ075-178-179.
NJ...None.
MARINE...None.
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&&

$$

SYNOPSIS...NV/DW
NEAR TERM...NV
SHORT TERM...NV
LONG TERM...NV/DW
AVIATION...DW
MARINE...NV/DW
HYDROLOGY...NV/DW
TIDES/COASTAL FLOODING...