000
FXUS61 KOKX 291801
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
201 PM EDT Fri Sep 29 2023
.SYNOPSIS...
An inverted surface trough and weak low move northward along the
coast today into tonight. The low will slowly strengthen and move
east Saturday into Sunday, with high pressure building in its wake
and remaining dominant into next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
***Scattered to Numerous Areas of Flash Flooding remain likely
today, with locally considerable to life threatening flash flooding
possible***
***Moderate Flooding expected for the Saddle River at Lodi and
is possible along a few quick responding small rivers and
streams***
There are many flood headlines ongoing across the western parts
of the region with flash flooding and river flooding. The area
is for parts of Northeast NJ, parts of NYC, parts of the Lower
Hudson Valley, and into Southwest CT.
There have already been storm total rainfall reports of near 3
to 6 inches across parts of the Lower Hudson Valley and into
parts of NYC. See our latest public information statement for
more details on exact rainfall amounts for exact locations.
Current Doppler Radar indicates heavy axis of rain extends from
east of Sandy Hook NJ northward through Brooklyn NY, Queens NY,
Nassau NY, Bronx NY, Westchester NY, and into Fairfield CT.
That is where the heaviest rain is ongoing with rainfall rates
between 0.5 and 1.5 inches per hour. Hourly rainfall rates
could occasionally reach around 2 inches per hour. The movement
is from southwest to northeast, driven by southerly flow of near
10-20 kt from 700 to 500mb. Near the surface, there are NE gusty
winds. The structure and dynamics show an environment conducive
for back building and training of heavy showers and they will
linger around throughout today. So multiple rounds of heavy
rain are expected to continue over the next few hours especially
across the the aforementioned sections mentioned in the
beginning of this paragraph.
Rain across Suffolk County NY and New Haven CT and east across
the rest of Southern CT has been light to moderate. Orange
County NY is also experiencing less rain, more light rain. The
area of concern is in between parts of NYC through Westchester
and Fairfield. CAMs show the heavy rain showers shifting
gradually and slowly farther east later this afternoon into
tonight.
Closed upper low over eastern Great Lakes will slowly approach
today, gradually sliding across the area tonight into Saturday. At
the surface, an inverted trough sitting off the NJ coast/mid
Atlantic coast will extend into NYC, NE NJ, W LI into Lower Hudson
Valley vicinity this morning. Evidence of a coastal
front/convergence zone across NYC and up Hudson River, which
could be a sign of where the inverted trough/coastal front ends
up extending into.
Continued good model agreement with increasing deep layered
lift from approaching upper low and left front quad of ULJ,
combined with a strengthening SE/E LLJ (35-40kt), transporting a
sub- tropical(+1-2 STD PWATS) and weakly unstable (a few
hundred J/kg of elevated instability) airmass into the region,
converging in the vicinity of the inverted trough/coastal front
(with likely frontogenetic and orographic enhancement). The
environment is certainly primed for deep moist convection and
flash flooding type rainfall in the Flood Watch area.
See hydrology sections for more on flood impacts.
In addition to the rain, NE winds of 15-20g25-30mph likely along the
coast this morning through Sat AM. A few peak gusts to 35 mph
possible. Lighter winds expected for the interior.
High temps will run several degrees below seasonable in rain and
onshore flow, and near seasonable for overnight lows.
&&
.SHORT TERM /SATURDAY/...
As the closed low moves overhead and low pressure becomes more
developed tonight into Saturday morning and gradually slides east,
the inverted trough/convergence axis will break down and slide east
with a more moderate deformation rain on the NW side of the low
continuing Tonight into Saturday morning, gradually tapering from w
to e.
High temps will run several degrees below seasonable in rain
and onshore flow, and near seasonable for overnight lows.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
There have been no significant changes to the long term, as
global ensemble guidance is in decent agreement with the overall
pattern. A rather quiescent and generally dry period is
expected along with a warm up into next week.
Closed, positively tilted upper low ejects off the east coast
to start, as a an amplified ridge shifts eastward from the
Central Plains. The ridge builds to the east Sunday through
Wednesday, with the ridge axis overhead by Wednesday. The ridge
axis heads offshore Wednesday night.
At the surface, low pressure heads east/southeast of the 40/70
benchmark on Saturday, with lingering showers across the
southern portions of the CWA though midday. Easterly flow will
continue through the day on Saturday, and into early Sunday,
keeping coastal sections under cloud cover for a good portion of
Saturday, while the interior should see some sun by late
afternoon. The pressure gradient begins to relax Sunday as the
surface low pulls away and winds become more northeasterly by
Sunday afternoon.
A strong high pressure then begins to dominate as it settles over
the northeast through Wednesday resulting in mainly dry conditions
for the region. Temperatures will be on the increase into midweek,
with highs in the mid to upper 70s across the NYC metro, northeast
NJ and the interior. At the coasts, highs in the low to mid 70s are
expected. Either way, these are near or just above average for the
time of year.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
An inverted trough across the area today will continue to bring
periods of moderate to heavy rain, gusty N-NE winds, and IFR
conditions. The rain will taper off on Sat as the sys slowly
exits.
IFR through tngt. CIGs improve gradually on Sat, but most of the
day is likely to be MVFR or lower. VFR possible aft 19-22Z,
although this may not occur if the sys is too slow to exit.
Winds will be N-NE at 10-20 kt with to around 25kt, highest at
the coastal terminals. Gusts will diminish this evening, but
increase again on Sat. Winds overall diminish aft 21Z Sat.
Moderate to hvy rain will continue, especially from JFK-LGA-HPN,
into this eve. Pockets of locally heavy rain will be possible
elsewhere, but uncertainty is higher. The heaviest rain is
expected to end by around 3Z, with mainly light rain lingering
into early Sat.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Winds may vary 20 degrees on either side due to the close
proximity of a surface trough thru this eve. Winds may be
stronger on Sat depending on how quickly low pres offshore
intensifies.
CIG/VIS variability possible due to the development/placement
of rain bands.
There is a chance of thunder at almost any time, but isolated,
so not included in the TAFs attm.
OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY...
Saturday: Improvement to VFR by around 00Z. N winds 15-25kt
possible.
Saturday Night: VFR with decreasing N winds.
Sunday through Wednesday: VFR.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
An extended period of SCA conds is expected for the ocean into early
next week. E/NE SCA gusts expected thru Sat, with seas elevating to
7 to 10 ft on E/SE wind swells, as well as background SE swells from
a developing offshore low and distant tropical systems impact the
coastal waters. E/NE Marginal SCA gusts expected on the nearshore
waters into Sat AM.
Winds gradually subside Saturday Night through Monday as high
pressure builds in from the west.
&&
.HYDROLOGY...
There have already been reports of near 3 to 6 inches of
rainfall across parts of NYC and across parts of the Lower
Hudson Valley.
Additional rainfall after 11AM this morning and through early
Saturday is forecast to range between 2 and 4 inches across much
of the area. Locally greater than 4 inches of additional
rainfall after 11AM is forecast especially for parts of
Westchester NY, Northern Nassau NY, Fairfield CT. Additional
rainfall after 11AM this morning, more in the 1 to 2 inch range
for Western Passaic NJ, Orange NY, New London CT, and the Twin
Forks of Long Island.
Another consideration is that the period of heaviest rain this
AM and this PM will coincide with two high tidal cycles where
minor flood thresholds are expected to be reached. This will
limit storm drainage capacity for coastal locations during these
times and exacerbate flash flood threat in these areas during
these times.
Based on the above, scattered to numerous instances of urban,
poor drainage, and low-lying flash flooding are likely in the
Flood Watch area, with locally considerable/life threatening
flash flooding possible.
In addition, river flooding is expected for Ramapo River at
Mahwah and Saddle River at Lodi and will be possible for other
rivers and streams through tonight.
&&
.TIDES/COASTAL FLOODING...
An approaching full moon will have rising astronomical tides (as low
as 1/4-1/2 ft needed to reach minor thresholds), combined with a
persistent and slightly strengthening E-NE flow and E wind
wave/swell today into Sat Am will have water levels solidly at minor
flood levels (up to 1 1/2 ft inundation) for vulnerable NY/NJ
harbor, Jamaica Bay, western Great South Bay, and coastal
Westchester/Fairfield communities, with localized minor elsewhere
across Long Island and NYC for the high tide cycles through at least
Saturday morning.
A bit more uncertainty on how widespread the minor coastal flooding
will be with the Saturday night and Sunday morning high tide cycles
as astronomical tides peak, but winds turn more to the N-NE and
gradually subside. Highest confidence in additional cycles of
widespread minor flooding is for the southern bays of Nassau and
Queens due to restricted tidal drainage, with perhaps more localized
minor flooding elsewhere.
In addition, continued beach erosion/escarpment will continue
through at least Saturday due to elevated water levels, 4-7 ft
breaking surf, and a strong E-W longshore current. Dune erosion
potential looks to be localized, with overwashes not expected.
Although our surf zone forecast season in over, the risk for
dangerous rip currents will continue into at least early next week
based on the wave conditions.
NOTE: The Peconic River at Riverhead tidal gauge is out of service
(had been reading too high). The gauge is being looked into by our
partners at the USGS.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch through late tonight for CTZ005-006-009-010.
Coastal Flood Advisory until 2 PM EDT Saturday for CTZ009.
NY...Flood Watch through late tonight for NYZ067>075-078>081-
176>179.
Coastal Flood Advisory until 2 PM EDT Saturday for NYZ071.
Coastal Flood Advisory until noon EDT Saturday for NYZ178-179.
NJ...Flood Watch through late tonight for NJZ002-004-006-103>108.
Coastal Flood Advisory until noon EDT Saturday for NJZ006-106-
108.
MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ331-332-
335-338-340-345.
Small Craft Advisory until 8 PM EDT Sunday for ANZ350-353-355.
&&
$$
SYNOPSIS...NV
NEAR TERM...JM/NV
SHORT TERM...NV
LONG TERM...DBR
AVIATION...JMC
MARINE...NV
HYDROLOGY...JM/NV
TIDES/COASTAL FLOODING...