000
FXUS61 KOKX 152046
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
446 PM EDT Sat Jul 15 2023

.SYNOPSIS...
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A frontal system approaches from the west tonight and becomes
nearly stationary across the area Sunday before moving east
Sunday night. High pressure will then briefly build across the
area Monday. Unsettled weather is likely to continue through the
rest of the week with the potential for a series of frontal
boundaries.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH SUNDAY/...
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A few strong storms will be possible through early this evening
in conjunction with enhanced low-level convergence from the
seabreeze and a weakening mid level cap. This will be mainly
focused from around the NYC metro and locations north and west.
Most of this should be short-lived due to a weakly sheared
environment. Localized heavy rainfall with rates of 1 to 2
inches an hour is also possible.

Flood Watch remains up for the entire forecast area late
tonight through Sunday evening.

The potential will exist for a significant flood event (possibly
major) late tonight through the day Sunday as a frontal system
works into the area ahead of another shortwave being sent east
out of the longwave trough. All the players are there with record
PWAT values of 2.25-2.50 inches, moderate-high instability, and
a slow-moving or at times stalled out boundary across the area.
There remains uncertainty as to where exactly the boundary puts
on its brakes with the CAMs varying in the placement of the
heaviest rainfall. Some differ with the highest QPF just NW of
the city, to others just east. Placement of this boundary will
be crucial to where the axis of heaviest rainfall sets up. In
addition, the 12Z NAMNest and SPC HREF mean highest QPF is just
NW of the NYC metro from interior NE NJ into the Lower Hudson
Valley and SW CT. The 18Z HRRR is more progressive and farther
east with the rainfall. Thus, there is no consensus and the
model error is such that small changes are likely even as we
get within a few hours of the event.

Rainfall amounts on average across the area are forecast to be
between 1 and 3 inches with localized amounts of 3 to 5 inches
possible. However, putting a cap on rainfall amounts,
especially in such a environment, may not be prudent. SPC HREF
Max QPF was 3 to 5 inches across the area, so this seems like a
reasonable start.

One late minute note, the 18Z NAMNest is showing some more
eastward progression like that seen in some of the other CAMs.
This would keep the rainfall more dispersed across the area,
which would be a better outcome. This trend will have to be
watched through the night and up until the event.

Warm, humid conditions continue through the period. Overnight
lows will be in the 70s, accompanied by dew points of similar
values. Clouds and rainfall on Sunday should result in a cooler
day, with highs around 80.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY NIGHT/...
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Lingering convection in the evening is forecast to work east of
the area during the early morning hours. The cold front is
expected to clear eastern LI/SE CT toward daybreak. Lows are
forecast to be a few cooler, ranging from the upper 60s inland,
to the lower 70s along the coast.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
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A persistent longwave upper trough will remain in place over eastern
North American through the time frame, with a series of shortwave
impulses riding through every other day or so this week with chances
for showers/tstms. On Mon we will be in between impulses and the day
should be very warm and somewhat humid, with highs mostly from the
upper 80s to lower 90s, and afternoon dewpoints from the mid 60s NYC
north/west to the lower 70s across Long Island and SE CT. The next
chance for organized convection arrives as the longwave trough axis
swings through, with a marginal risk of excessive rainfall fcst for
the Hudson Valley. Slightly cooler high temps (85-90) and slightly
higher dewpoints (upper 60s/lower 70s) on Tue should yield similar
heat index values to those of Monday.

Max heat index values for the two days should be mostly below 95,
with the possible exception of the urban corridor of NE NJ and some
spots along the north shore of Long Island, with only E Union County
meeting local heat advy criteria of two consecutive days of 95+ heat
index.

Some haze may also be possible Mon night into Tue, per extrapolation
of latest HRRR guidance suggesting some smoke from western Canada
wildfires crossing the Appalachians during that time.

Wed looks like a mostly dry day with shortwave ridging briefly
moving across, then the next organized chance of showers/tstms
should arrive Thu-Fri as the longwave upper trough becomes re-
established. Forecast per NBM currently shows dry conditions for Sat
but confidence in this is low especially east of NYC with
deterministic global models showing a wave of low pressure moving
NNE through the adjacent Atlantic waters.
-- End Changed Discussion --

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
A frontal boundary will remain in the vicinity of the terminals
through tomorrow.

VFR through this evening. Scattered showers and thunderstorms
possible mainly inland late this afternoon into early this
evening, with low confidence in timing and coverage. Most likely
window is from 19-23z. Only have enough confidence to include
TEMPO at KTEB, KEWR and KSWF for now, but the chance remains for
all terminals except KISP and KGON.

More widespread showers and thunderstorms by late tonight, with
heavy rain at times, with MVFR to IFR, and possibly LIFR.
Development may be an hour or two earlier than forecast. Showers
and thunderstorms continue through Sunday.

A southerly flow is expected through the forecast period. At or
below 10 kt today and at or above 10 kt on Sunday.


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

A few scattered thunderstorms will be possible late afternoon
into early this evening and included TEMPO at KEWR and KTEB,
lower chances that thunder occurs at KJFK and KLGA, and may be
included later.

Timing of MVFR to possibly IFR stratus moving into KJFK and KLGA
this evening is uncertain. High confidence in low end MVFR cigs
overnight through early tomorrow, lower confidence in IFR.

Uncertainty in end time of SHRA and TSRA on Sunday. Held on to
a VCTS for a few more hours after PROB30 for TSRA ends. There is
a chance for TSRA to linger through the end of the TAF period.


OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY...

Sunday Afternoon: MVFR to IFR in numerous showers with a chance
of thunder early afternoon.

Monday: Early morning MVFR possible in cigs/vsby, especially
east of the NYC terminals, becoming VFR.

Tuesday: MVFR or lower in chance of showers and thunderstorms.

Wednesday: VFR.

Wednesday Night - Thursday: MVFR or lower in chance of showers
and thunderstorms.

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

&&

.MARINE...
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Ahead of an approaching frontal system, southerly winds will
strengthen to around 15 kt on the ocean waters by morning,
increasing seas around 5 ft. A SCA has been issued for Sunday
and Sunday night between Fire Island Inlet and Montauk Point.

Sea up to 5 ft may linger on the ocean waters daytime Mon per NWPS
and GFSwave, especially out east. Confidence in this is low as
sustained winds in the persistent S flow daytime Sunday peak only
briefly between 15-20 kt, and will be lighter out of the SW daytime
Mon, so SCA has not been extended into this time frame.
-- End Changed Discussion --

&&

.HYDROLOGY...
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A Flood Watch is in effect for the entire CWA late tonight and
Sunday.

There is the potential for a significant to major flood event on
Sunday as a frontal boundary works across the area. All of the
area except eastern LI is under a Moderate Risk for Excessive
Rainfall. The potential is there for scattered to numerous flash
floods. On average, widespread rainfall of 1 to 3 inches, with
localized amounts of 3 to 5 inches will be possible.

A marginal risk of excessive rainfall is forecast for the Hudson
Valley for Tuesday, as another passing disturbance helps generate
showers/tstms with heavy rainfall. An ongoing risk may continue with
successive systems later this week.
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&&

.TIDES/COASTAL FLOODING...
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There is a high risk of rip current development at all the ocean
beaches Sunday into Monday as southerly swells increase.
-- End Changed Discussion --

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Flood Watch from midnight EDT tonight through Sunday evening
     for CTZ005>012.
NY...Flood Watch from midnight EDT tonight through Sunday evening
     for NYZ067>075-078>081-176>179.
     High Rip Current Risk until 9 PM EDT this evening for NYZ075-
     080-081-178-179.
NJ...Flood Watch from midnight EDT tonight through Sunday evening
     for NJZ002-004-006-103>108.
MARINE...Small Craft Advisory from 8 AM Sunday to 6 AM EDT Monday for
     ANZ350-353.
-- End Changed Discussion --

&&

$$

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