000
FXUS61 KOKX 122049
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
449 PM EDT Tue Sep 12 2023

.SYNOPSIS...
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A wave of low pressure approaches along a cold front tonight. The
low and front move across the region Wednesday and then move east of
the region Wednesday night. High pressure then builds in behind
the departing cold front and remains centered over the Great Lakes
through Friday. The high starts to weaken over the weekend. At
the same time, Tropical Cyclone Lee is forecast to pass offshore
to our east.

Monitor https:/www.weather.gov/okx/tropical or
https:/www.nhc.noaa.gov for the latest NHC forecasts on Hurricane
Lee and others.
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&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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In the upper levels, a southwesterly jet approaches from the Great
Lakes. In the mid levels, the ridge moves farther east and
height falls will portend the approach of a trough. The positive
vorticity advection will increase late tonight. At the surface,
a weak wave of low pressure approaches along a cold front. The
main parent low will be in Quebec.

Clouds increase in coverage going into the overnight period with
increasing chances of rain showers. Thunderstorm chances develop
as well going into early Wednesday morning with the increase in
low level instability.

Forecast lows are on the warmer side with a combination of NBM
and consensus of all model guidance used, ranging from the low
60s to near 70.
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&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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Showers can be expected with heavy rain at times across the
entire area Wednesday, lingering into Wednesday night for
Southeast CT and Eastern Long Island as a cold front with
associated wave of low pressure move across. See hydro section
for details regarding the potential for flooding and the flood
watch in effect for the region. There is a marginal threat for
severe weather as well discussed more below.

The mode of convection will likely be a solid to broken squall
line moving into western sections of the region early Wednesday
morning and across the remainder of the region for the remainder
of Wednesday morning into afternoon. This is from analysis of
CAMs. Wednesday morning through Wednesday afternoon is when
much of the rainfall is expected.

In the upper levels, the southwesterly jet intensifies farther
south with the right rear quad of this jet close to the forecast
region.

For the mid levels, the positive vorticity advection will continue
to increase from west to east. Mid level height falls will continue
as the trough continues to approach from the west. The weak wave of
surface low pressure along the cold front will gradually move east
within the region Wednesday.

On Wednesday night, the upper level jet streak narrows and
intensifies north of the region. The mid level height falls continue
as eventually the trough axis moves in by early Thursday. At the
surface, the front and low pressure wave will both exit east of Long
Island.

Layer precipitable waters increase to nearly 2 inches Wednesday
and with parallel flow evident from low to upper levels in the
forecast models, training of showers and thunderstorms can be
expected which will mean multiple rounds of showers and
thunderstorms. CAPE profiles from BUFKIT soundings are tall and
narrow but there will be more shear than what was present back
on Monday, allowing for thunderstorms to have more movement.
This will somewhat limit the extent of flooding but with intense
enough thunderstorms, flash flooding cannot be ruled out. The
higher shear will allow for potential for some strong to severe
thunderstorms as well. CAPE will be limited but more
directional wind shear in the low levels will increase helicity.
There will be the possibility for some thunderstorms to have
damaging winds as well as exhibit rotation so a brief tornado
will be possible as well.

Showers are most widespread across western sections of the
region including NE NJ, NYC, Lower Hudson Valley, Western Long
Island and SW CT Wednesday morning into early Wednesday
afternoon. Showers are most widespread across eastern sections
of the region with the rest of Southern CT and Eastern Long
Island Wednesday morning through early Wednesday evening. There
is potential for showers and thunderstorms to linger for a
longer period of time for these eastern sections Wednesday
night.

Forecast highs Wednesday are on the cooler side and were chosen
from the consensus of all model guidance, only ranging from the
low to mid 70s. Expecting temperatures to be a little cooler
with the more northerly flow Wednesday night with a blend of
MAV, MET and NBM used for lows, ranging from the low 50s to low
60s.
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&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
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On Thu showers should be coming to an end out east early AM,
otherwise looking at a mostly sunny day with NW flow ushering a
drier air mass, with dewpoints lowering to the 40s/lower 50s.

For Fri, high clouds in advance of Lee will be on the increase,
otherwise temps/dewpoints look similar to those for Thu. Northerly
winds between inland high pressure and Lee will also be on the
increase to 15G25mph as the pressure gradient increases between
inland high pressure and the outer circulation of Lee.

Strongest winds associated with Lee should arrive Fri night and
continue into Sat, with winds backing NW on Sat as the hurricane
passes well east. The hurricane`s wind field will be expanding in
size as it moves northward, and winds especially across coastal SE
CT and ern Long Island could become strong, sustained 25-30 mph with
gusts up to 40 mph possible. Can`t rule out tropical storm force
winds in those areas right near the shoreline in areas with a good
NW-N exposure.

NBM PoP still clips ern CT/Long Island on the periphery of Lee, with
only light rainfall amts expected at most.

WAA starts early next week, with slight chance for showers and
possibly a tstm Mon/Tue.
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&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
A cold front approaches tonight and moves across the terminals
on Wednesday.

Generally looking at VFR conditions for the remainder of the
afternoon and evening. Tonight, we start off VFR and should
remain VFR for much of the night, until conditions fall to MVFR
or lower in chances of rain around 08-10z. Hi-res forecast
guidance showing line of showers and thunderstorms moving
through the terminals during the morning push (11-14z) and have
included a tempo to cover this threat. Lesser confidence of
thunder after 14z, but still can not rule out some leftover
convection, will continue with a PROB30 from 14-18z to address
this threat. Timing of convection will be slightly later for the
terminals east of NYC.

Winds gradually shift to the south during the afternoon as sea
breezes develop, then the synoptic flow turns more southerly and
remains light overnight. Winds are expected to become more
westerly then northwesterly behind the front on Wednesday,
mainly after 18z.

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

Timing of wind direction changes may be off by an hour or two.

Amendments may be needed to fine tune timing of thunder on
Wednesday.

OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY...

Wednesday: Any leftover Showers and/or thunderstorms taper off,
with a return to VFR for any terminals below VFR conditions.

Thursday - Friday: VFR. Northerly wind gusts around 15 to 20 kt
Thursday night through Friday night.

Saturday: Mainly VFR. NW wind gusts around 20 to 25 kt.

Sunday: VFR. West winds with gusts 15-20kt.

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

&&

.MARINE...
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Ocean seas are building with long period swells already being
observed. Wavewatch and SWAN guidance have come in earlier with
5 ft seas later tonight so small craft advisory was adjusted to
start earlier for ocean zones west of Moriches Inlet NY,
starting 2AM Wednesday and still begins at 6AM Wednesday from
Moriches Inlet NY to Montauk Point NY. The small craft advisory
goes until 6AM Thursday for all ocean zones. Non-ocean waters
remain below SCA threshold through Wednesday night. Winds remain
below SCA thresholds through Wednesday night.

Ocean seas should continue to build through the week, reaching 5-8
ft by late day Thu, 8-12 ft by daybreak Fri, and peaking at 9-14 ft
Fri afternoon/evening. Seas will then actually start to slowly
decrease Fri night into Sat as strong offshore flow counteracts
incoming swell, down to 8-12 ft by daybreak Sat, 6-8 ft Sat evening,
then below 5 ft by Sunday afternoon.

Attm think sustained N-NW winds or frequent gusts from Lee could
peak at tropical storm force (35-40 kt) Fri night into Sat, mainly
on the ern ocean waters/sound. Elsewhere, SCA cond likely from Fri
into Sat, with a few gusts up to 35 kt possible Fri night/Sat
AM.
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&&

.HYDROLOGY...
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Around 1 inch of rain is forecast for most locations from late
tonight through Wednesday evening with locally higher amounts
expected. The upper limit for these locally higher rainfall
amounts would be 2 to 3 inches locally.

There is a chance for flash flooding with any areas receiving
multiple rounds of showers and thunderstorms with heavy rain
especially in low lying, poor drainage and urban areas. A flood
watch is in effect for NE NJ, NYC, Lower Hudson Valley, Nassau
NY, and Fairfield CT from 4AM until 6PM Wednesday and a flood
watch is in effect for New Haven CT, Middlesex CT, and New
London CT as well as Suffolk NY from 8AM Wednesday until 2AM
Thursday.
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&&

.TIDES/COASTAL FLOODING...
There is a moderate rip current risk today, then a high risk
thru the rest of the week as swell continues to build. A high
risk statement has been issued thru Fri, and may need to be
extended thru at least Sat depending on the ultimate track,
intensity and timing of Lee.

A high surf advy may be needed Fri.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Flood Watch from 4 AM EDT Wednesday through Wednesday
     afternoon for CTZ005-009.
     Flood Watch from Wednesday morning through late Wednesday
     night for CTZ006>008-010>012.
NY...Flood Watch from 4 AM EDT Wednesday through Wednesday
     afternoon for NYZ067>075-176>179.
     Flood Watch from Wednesday morning through late Wednesday
     night for NYZ078>081.
     High Risk for Rip Currents from Wednesday morning through Friday
     evening for NYZ075-080-081-178-179.
NJ...Flood Watch from 4 AM EDT Wednesday through Wednesday
     afternoon for NJZ002-004-006-103>108.
MARINE...Small Craft Advisory from 6 AM Wednesday to 6 AM EDT Thursday
     for ANZ350.
     Small Craft Advisory from 2 AM Wednesday to 6 AM EDT Thursday
     for ANZ353-355.
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&&

$$

SYNOPSIS...BG/JM
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...BG
AVIATION...BC
MARINE...BG/JM
HYDROLOGY...BG/JM
TIDES/COASTAL FLOODING...