000
FXUS61 KOKX 281831
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
231 PM EDT Thu Sep 28 2023
.SYNOPSIS...
High pressure to the north today will give way to an inverted
surface trough and weak low moving northward along the coast
tonight into Friday. The low will move slowly strengthen and
move east Friday Night into Saturday, with high pressure
building in its wake and remaining dominant into next week.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Upper ridging over New England slowly slides east today as a
closed upper low over the Great Lakes slowly slides east towards
the area. At the surface, an inverted trough off the Mid
Atlantic coast gradually extends north this aft/eve as Canadian
high pressure slides off New England.
Stratus development today across southern and western portions
of the area due to an increasingly moist onshore flow under an
850mb subsidence inversion. The stratus deck will gradually
working N/NE thru the aft. Additionally, the approaching closed
low, strengthening llj and theta-e advection will bring
increasing chances for light showers across NE NJ/NYC and LI
this afternoon, gradually working N through this evening. Timing
and N/NE extent of showers is a bit uncertain with subsidence
and dry air to contend with.
Onshore flow and cloud cover will keep temps several degrees below
seasonable today (mid 60s), warmest across SE CT with more in
the way of sunshine.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
Models in good agreement with closed upper low continuing to
approach tonight into Friday, gradually sliding across the area
Friday Night into Saturday. At the surface, sprawling high
pressure remains over New England, although with its center
moving offshore. This will allow an inverted trough/surface low
sitting off the Mid Atlantic coast to slide towards the region
Friday and then gradually sliding southeast of the area Friday
Night/Saturday.
Good general agreement with increasing deep layered lift from
approaching upper low and right front quad of ULJ, combined
with a strengthening SE/E LLJ Tonight/Fri, transporting a sub-
tropical airmass (+1-1.5 STD PWATS) into the region, converging
in the vicinity of an inverted trough/coastal front (with
possible deformation zone and orographic enhancement) for a
6-12 hr period across portions of the area late tonight thru
Friday. Also can rule out a bit of elevated instability across
southern and western portions of the Tri-State with approach of
upper low on Friday, increasing deep convection. The signal for
an axis of heavy rain in the vicinity of the area is strong,
but model spread between ensemble, deterministic and high res
model solutions exists in the exact location and duration of
this mesoscale convergence zone where heaviest rain will fall.
As far as ensembles, prob of 2" rain in 24 hrs (mainly Friday)
ranges from High (60-70% GEPS prob for NYC and pts east), High
(70-80% ECE prob for eastern portions of the region), to Low
(10-20% GEFS prob for eastern portions of the region). NBM has
a 30-40% prob of 2"/24 hrs, 15% prob of 3"/24 hr for Friday across
NYC/NJ metro, Lower Hud, SW CT and LI. Note: This is a
considerable upward trend in 2" probs from single digit probs
over the last 24 hrs.
As far as high res solution guidance, 00z HREF, which is just now
covering the Friday day period has a broad 10% ensemble prob of
3"/3hr across NYC, NJ, and Lower Hud, with a bullseye of 30%
ensemble prob of 3"/3hr across NE NJ. This 30% 3"/3hr tends to
be an elevated signal for flash flooding potential (w/ typical
location uncertainty), if this heavy rain axis ends up over the
urban and flashy river basins in this area. Headwater guidance
for several of the flashy streams in NE NJ is around 2- 2 1/2"
in 6hr for minor, and 2 1/2 to 3 1/2 in 6 hr for moderate
flooding, which is a bit concerning if this all comes together
across this region (HREF 6 hr PMM is signaling potential for
3-5" in 6hr Fri morning in afternoon west of the Hudson R.).
So needless to say, a good signal for a heavy rain axis
presenting a urban and poor drainage and flashy river basin
flood threat, with a conditional localized to scattered flash
flood potential, but low confidence on location. With this
location/duration uncertainty, lack of model to model and run to
run consistency, and this being the first cycle of HREF
resolving this time period, will hold off on flood watch at this
time. But if the heavier QPF solutions remain consistent, a
Flood Watch will likely be needed for portions of the area,
particularly if the heavy rain axis is expected over NYC, NE NJ,
Lower Hud, and SW CT.
As the closed low moves overhead and low pressure becomes more
developed Fri Night into Saturday and gradually slides east,
the inverted trough/convergence axis should break down and slide
east with a more general deformation rain on the NW side of the
low continuing Friday Night into Saturday morning, gradually
tapering from w to e.
In addition to the rain, NE winds of 15-20g25-30mph likely along the
coast Fri AM through Sat AM. A few peak gusts to 35 mph possible.
Lighter winds for the interior.
High temps will run several degrees below seasonable in rain
and onshore flow, and near seasonable for overnight lows.
&&
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
A high amplitude upper level ridge over the Mississippi Valley will
translate east during the period. This will result in a dry,
unseasonably warm period. A weakening backdoor cold front slips
through Sunday night into Monday morning with little if any change
in airmass. Surface high pressure builds in from the west through
Tuesday and then offshore by mid week.
High temperatures during the time will generally be in the 70s, even
approaching 80 across the NYC metro and inland areas. The warmest
days at this time look to be Tue and Wed with 85h temps around 15C,
possibly a bit higher. Lows will generally be 55 to 60. On average,
departures look to be about 5 degrees above normal.
&&
.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
An offshore inverted trough works toward the area today and
across the area tonight into Friday.
MVFR ceilings prevail for all but the CT terminals this
afternoon. A few showers expected this aftn for most of the
terminals. Ceilings will then lower tonight to IFR everywhere
as steady rain moves in. IFR likely prevails through Friday with
periods of rain. Rain will be heavy at times tonight into Friday.
NE winds 10-15 kt. Gusts develop to around 20 kt for the
overnight hours, primarily for the coastal terminals.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Occasional gusts to around 20kt possible as early as around
00z, especially at KLGA. Brief MVFR vsbys in -shra possible
this aftn and early evening. Timing of IFR onset may be off by a
few hours. TEMPO LIFR cigs might not occur late tonight and
Friday morning, but it`s also possible LIFR can prevail for a
few hours during that time.
OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY...
Friday PM: IFR and rain. NE winds G15-25 kt, highest at the
coastal terminals.
Saturday: MVFR/IFR and -shra in the morning, improving to VFR
by late. NE winds G15-20kt mainly at the coastal terminals.
Sunday and Tuesday 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 likely for the ocean into early
next week. SCA gusts are likely late tonight into Sat AM, with seas
elevating to 6 to 8 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. Marginal SCA gusts possible on the
nearshore waters late tonight into Sat AM, but otherwise
expected to be below SCA.
Winds and seas will gradually subside Saturday aft through
Monday as high pressure builds in from the west with diminishing
winds and decreasing seas. SCA seas likely remain on the ocean
waters during this time, subsiding to around 5 ft by Monday.
&&
.HYDROLOGY...
Potential is increasing for a widespread 2-3" of rain across
the region Tonight into Saturday morning. High-res guidance
indicating potential for a localized swath of 3-5"+ in 6 hr Fri
AM/PM (10-30% prob of 3"/3hr, with spotty 10-20% prob of
1"/hr), but low confidence on development or location of this
type of rainfall axis at this time. Based on this conditional
threat, a slight risk of flash flooding has been coordinated
with WPC for the region.
With recent rains, headwater guidance for several of the flashy
streams in NE NJ is around 2-2 1/2" in 6hr for minor flooding,
and 2 1/2 to 3 1/2" in 6 hr for moderate flooding, which is a
bit concerning if this all comes together across this region.
Another consideration is that the period of heaviest rain Fri AM
into 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.
So, a good signal for a minor urban and poor drainage and
flashy river basin flood threat, with a conditional localized to
scattered flash flood potential if/where heavy rainfall axis
materializes, but low confidence on location. With this
location/duration uncertainty, lack of model to model and run to
run consistency, and this being the first cycle of HREF
resolving this time period, will hold off on flood watch at this
time. But if the heavier QPF solutions remain consistent, a
Flood Watch will likely be needed for portions of the area,
particularly if the heavy rain axis is expected over NYC, NE NJ,
Lower Hud, and SW CT.
&&
.TIDES/COASTAL FLOODING...
Localized minor coastal flooding possible mainly in the most
vulnerable south shore bays of Nassau locations this morning.
Thereafter, 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 LI and NYC
for tonight, Fri AM, Fri PM and likely the Sat AM high tidal
cycles.
A bit more uncertainty on how widespread the minor coastal
flooding will be with the Sat PM into Sun high tidal cycles as
astronomical tides will peak, but winds will turn more to the
N/NE and gradually subside. Highest confidence in additional
cycles of widespread minor flooding are 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 to 7
ft breaking surf, and a strong E to W long shore 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 current 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...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT
Friday for CTZ009.
Coastal Flood Advisory from 10 AM to 1 PM EDT Friday for
CTZ009.
Coastal Flood Advisory from 10 PM Friday to 2 AM EDT Saturday
for CTZ009.
NY...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT
Friday for NYZ071.
Coastal Flood Advisory from 10 AM to 1 PM EDT Friday for
NYZ071.
Coastal Flood Advisory from 10 PM Friday to 2 AM EDT Saturday
for NYZ071.
Coastal Flood Advisory from 6 PM this evening to midnight EDT
tonight for NYZ178-179.
Coastal Flood Advisory from 7 AM to 1 PM EDT Friday for NYZ178-
179.
Coastal Flood Advisory from 7 PM Friday to 2 AM EDT Saturday
for NYZ178-179.
NJ...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for
NJZ006-106-108.
Coastal Flood Advisory from 7 AM to 11 AM EDT Friday for
NJZ006-106-108.
Coastal Flood Advisory from 7 PM Friday to midnight EDT Friday
night for NJZ006-106-108.
MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ350-353-
355.
&&
$$
SYNOPSIS...NV/DW
NEAR TERM...JMC/NV
SHORT TERM...NV
LONG TERM...DW
AVIATION...JC
MARINE...NV/DW
HYDROLOGY...NV/DW
TIDES/COASTAL FLOODING...