discussion on 2023-08-10

000
FXUS61 KOKX 101943
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
343 PM EDT Thu Aug 10 2023

.SYNOPSIS...
-- Changed Discussion --Low pressure passes near Long Island this evening before
exiting to the north and east. High pressure follows for Friday,
with a frontal system moving across the area late Saturday into
early Sunday. High pressure then briefly returns again before
another storm system moves in late Monday. High pressure returns
for mid- week. A weak cold front may pass on Wednesday.-- End Changed Discussion --

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
-- Changed Discussion --Surface analysis late this afternoon indicates a weak area of low
pressure with a warm front draped just to our south and west. This
will advance toward the region into the evening, with rain
overspreading the region as it does so, and may fall moderate to
heavy at time. The primary concern with this system is the potential
for heavy rainfall leading to nuisance flooding. PWATs approach
or exceed 2 inches this evening, and upward forcing in the vicinity
of the low center, along with some upper level divergence courtesy
of a jet streak nearly overhead could enhance rainfall. The main
limiting factor for flooding potential will be the progressive
forward motion of the system. Overall, QPF averages between a
quarter inch and three quarters of an inch, with locally heavy
amounts.

Low-level helicity values increase with the nearby warm front, and
given the elevated shear, can`t entirely rule out an offshore
waterspout or even a brief spin up on land, particularly coastal
areas. SPC has a 2% tornado risk outlined for Long Island, NYC, and
NE NJ. Have already observed several rotating cells across
southern New Jersey from nearby KDIX and TPHL.

Conditions dry out west to east with the fropa in the evening
hours, and the entire region should be rainfree by midnight or
so. Winds veer westerly tonight and skies begin to clear as
temperatures fall into the 60s.-- End Changed Discussion --

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
-- Changed Discussion --The trough swings east on Friday and heights rise some in response.
At the surface, weak high pressure builds into the area, maintaining
a light W/WNW flow.

Dew points drop into the 50s behind the frontal passage, and coupled
with temperatures in the low to mid 80s, should make for a pleasant
August afternoon under just a bit of daytime cu. Given the
sunshine and downsloping winds, used the NBM 75th percentile for
highs, with low-to-mid 80s once again expected, and perhaps
some upper 80s in the urban metro.

With the light winds and relatively clear skies, blended in the
MAV/MET guidance for lows Friday night, with some parts of the
lower Hudson Valley and the LI Pine Barrens likely falling into
the 50s toward daybreak Saturday. Except for what is already
noted, primarily followed the superblend of guidance for this
update.-- End Changed Discussion --

.LONG TERM /SATURDAY THROUGH THURSDAY/...
-- Changed Discussion --A weak trough with rising heights remains in influence Saturday
morning with surface high pressure nearby. This changes as troughing
develops out ahead of an approaching cold front Saturday afternoon.
Ahead of the front, south and west winds will bring up dewpoints with
the front providing a good source of lift for showers and
thunderstorms. Coverage is expected to be scattered in the afternoon
will a increase in coverage at night as the front passes due to
enhanced forcing along the front. SPC currently has a marginal risk
of severe weather for our area. Model guidance still varies on the
available instability for thunderstorms. The 12Z NAM has SBCAPE as
high as 2000-3000 J/kg while the GFS sits between 1000-1500 J/kg
with only a few small spots of 2000 J/kg. The 6Z ECMWF sits
somewhere in between the GFS and NAM guidance. Its possible a stray
storm or two could produce wind gusts near 60 mph, with most storms
expected to remain sub-severe at this time, but this is subject to
change as more convective-allowing guidance becomes available.

Sunday a northwest wind sets up with drying conditions behind the
cold front. SUnnier skies should allow temperatures to warm into the
mid-upper 80s, with even a few near 90 forecasted in NE NJ and in
the NYC metro.

Monday should start off dry with south winds quickly leading to
rising dewpoints ahead of an overnight cold front. 12 GFS is
currently putting out PWATs of 2.25-2.5". The 90% percentile from
SPC`s sounding climatology page is 1.75" with the max moving average
around 2.15". This, along with sufficient forcing along a cold front
could lead to locally moderate to heavy downpours, at times. WPC
currently has the region under a marginal risk for excessive
rainfall. Its still a good ways away, but worth watching to see if
the signals for heavy rain trend heavier or weaker. The good news is
the system looks to be quite progressive, which hopefully means we
shouldn`t see any slow moving showers. The signal for thunderstorms
doesn`t look as great as Saturday, but could still see isolated to
scattered thunderstorms with some of the strongest areas of forcing.

After the front clears Tuesday morning, clouds should clear allowing
for sunny skies to return for Tuesday afternoon before a weak front
impacts us on Wednesday. Some showers and thunderstorms are possible
with the FROPA, but not looking significant at this time.-- End Changed Discussion --

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --Low pressure will pass over or just south of the terminals this
evening.

VFR have begun to deteriorate to MVFR for western terminals with
moderate to heavy showers moving through. Conditions lower to MVFR
for the rest of the area as the afternoon and evening progresses.
IFR conditions are possible but will probably be limited to heavier
showers and thunderstorms. Thunderstorms are currently to the
southwest and west of the metro terminals. If they hold together,
they should make their way to the metro terminals between 20 and
21Z, so cover them with a TEMPO group between 20-22Z. A return to
VFR is expected around 03Z for the metro terminals, with later
improvements as you go east (around 07Z for KGON). However, this
could be a couple of hours off as the back of of main precipitation
shield is currently over western New Jersey. So, VFR conditions may
return a couple of hours earlier than is currently forecast.

Generally, a S wind this shifts to the W by around 03Z as the low
exits the area. Thereafter, a W to WNW flow sets up through the end
of the TAF period. There may be an isolated gust of around 20 kt
this afternoon and evening, but for the most part, gusts should be
limited to thunderstorm activity.

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

Amendments likely due to timing of flight rule category changes,
thunderstorms, and possible for wind direction later this evening,
depending on when the low exits the area.

OUTLOOK FOR 18Z FRIDAY THROUGH MONDAY...

Friday: VFR.

Saturday-Sunday: Mainly VFR. Chance of showers, possibly
thunderstorms, late Saturday into Sunday.

Monday: VFR early, then a chance of MVFR with a chance of showers
and thunderstorms.

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

.MARINE...
-- Changed Discussion --South/southwest winds may produce a few isolated gusts around 25 kt
into this evening before subsiding behind a frontal passage tonight.

Otherwise, sub-SCA conds expected on all waters through Monday
afternoon. Monday night wind gusts over ocean waters could
approach 25 kts.-- End Changed Discussion --

.HYDROLOGY...
-- Changed Discussion --A basin average of 0.25 to 0.75 inches of rainfall with the
potential of locally higher amounts is forecast into this evening.
Mainly minor/nuisance flooding is expected with this system but
flash flooding cannot be completely ruled out. Should flash
flooding occur, the most likely area to see it would be in NE NJ
and NYC where it`s typically more prone to flooding.

No anticipated hydrologic impacts Saturday and Sunday. Late Monday
into Tuesday, brief periods of moderate to heavy rainfall could
occur ahead of a cold front leading to isolated flooding concerns.
After Monday morning, no hydrologic impacts are expected for the
rest of the forecast period.-- End Changed Discussion --

.TIDES/COASTAL FLOODING...
-- Changed Discussion --There is a moderate risk for rip currents on ocean beaches Friday
and Saturday.-- End Changed Discussion --

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

$$
SYNOPSIS...DR
NEAR TERM...JC/DR
SHORT TERM...DR
LONG TERM...BR
AVIATION...JP
MARINE...BR/DR
HYDROLOGY...BR/DR
TIDES/COASTAL FLOODING...BR