000
FXUS61 KOKX 292009
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
409 PM EDT Fri Sep 29 2023
.SYNOPSIS...
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Low pressure will be moving southeast of Long Island tonight
into Saturday while slightly strengthening. The low pressure
area will slowly move farther east out into the Atlantic
Saturday night into Sunday. Thereafter, high pressure will build
in from the Great Lakes through much of next week.-- End Changed Discussion --
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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***Flash flood watch remains through tonight for continued
potential for considerable flash flooding***
Heaviest rainfall axis in Nassau, NW Suffolk and going north
into Fairfield CT where greatest threat for flash flooding
exists. Elsewhere in flash flood watch area, still chances for
flash flooding but threat overall decreases late tonight.
Middlesex and New London CT, still on lower end of rainfall
amounts so did not expand flash flood watch in those zones.
The flash flood watch remains in effect to cover any
backbuilding and evolution of current heavy rainfall across the
area. Elevated instability will be confined to more coastal
areas so have isolated/slight chance thunderstorms in the
forecast for those locations.
With strengthening low pressure moving southeast of Long Island
and the inverted trough slowly moving eastward within the local
region, there will be enhanced convergence and vertical lift
going into tonight. Mid level cutoff low moves overhead.
CAMs are indicating backbuilding and expansion of heavy rain
showers going into tonight across mainly western portions of the
area. At this point, do not want to make any changes to the
flood watch still out through tonight. The bulk of the rainfall
be through early this evening. Before 8PM, still could have
forecasting additional 1 to 3 inches of rain across parts of NE
NJ, NYC, Lower Hudson Valley, SW CT and Western Long Island.
SREF has some 850-500 mb Q vector convergence and model bufkit
shows maxes in low to mid level omega going into early evening.
Both parameters decrease going into later this evening.
Layer precipitable waters up to 1.6 inches across the coastal
sections of the region which models only have decreasing
slightly this evening down to around 1.4 to 1.5 inches. However,
forcing is shown by models to decrease this evening after 8PM.
Have heaviest of rain shifting farther east more across Long
Island and Southern Connecticut later this evening into
overnight. Overall, think the rainfall intensity will be on a
downward trend late tonight into dawn of Saturday. However,
keeping POPs in likely at least with lingering rain showers
overnight with mid level positive vorticity advection.
NE gusty winds remain across the coastal sections of the region
through tonight. Lows were taken from a consensus of raw model
data, ranging from the mid to upper 50s. Temperatures will
likely be right near the dewpoint with the saturated low levels
in place.-- End Changed Discussion --
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
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Low pressure moves farther away southeast of Long Island
Saturday into Saturday night with mid level cutoff low moving
southeast of Long Island also. Vertical RH lowers considerably
between 850 and 500 mb during the day Saturday. Rain showers
will linger across the region Saturday morning and then
gradually taper off from NW to SE in the afternoon across the
interior areas. Rain showers in the forecast do not taper off
for Eastern Long Island and Southeast CT until early Saturday
evening. Drier conditions move in Saturday night with any
remaining chances for rain showers decreasing for the Twin Forks
of Long Island. Mainly dry conditions are anticipated for
Saturday night.
Max temperatures forecast Saturday were taken from a consensus
of raw model data, ranging from the mid 60s across western
sections to lower 60s across eastern sections. Min temperatures
Saturday night were taken from a consensus of MOS, ranging from
the upper 40s to upper 50s.-- End Changed Discussion --
&&
.LONG TERM /SUNDAY 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 /19Z FRIDAY THROUGH WEDNESDAY/...
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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...
Tstms developing over the ocean tracking nwd will likely impact
JFK/LGA into this eve. A tempo has been included. Otherwise, isold
tstms thru this eve but probs too low to include in the TAFs.
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.
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...
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SCA conditions expected on all waters. SCA for the ocean goes
until 8PM Sunday. SCA for non-ocean waters goes until 8PM
Saturday. There may be some occasional 25 kt gusts for eastern
non-ocean waters Saturday evening. Otherwise, mainly below SCA
conditions expected for non-ocean waters Saturday night.
Winds gradually subside Saturday Night through Monday as high
pressure builds in from the west.-- End Changed Discussion --
&&
.HYDROLOGY...
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There have already been reports of near 1 to 7 inches of
rainfall within the forecast region. Highest amounts have been
in eastern parts of NYC, Westchester NY, Nassau NY and Fairfield
CT.
Additional rainfall after 2PM this afternoon and through early
Saturday is forecast to range between 2 and 3 inches across
much of the area with locally higher amounts expected, especially
for parts of Westchester NY, Nassau NY, and Fairfield CT.
Additional rainfall after 2PM this afternoon, more in the 1 to
2 inch range for Western Passaic NJ, Orange NY, New London CT,
and the Twin Forks of Long Island.
Next high tide cycle going into tonight could very well
exacerbate flooding issues along the coast.
Some river and stream flooding is expected.
Saturday and beyond, outside of any residual flooding and rivers
that are elevated, no additional significant rainfall is
expected.-- End Changed Discussion --
&&
.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...JM/NV
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...DBR
AVIATION...JMC
MARINE...JM/NV
HYDROLOGY...JM
TIDES/COASTAL FLOODING...