discussion on 2023-09-24

000
FXUS61 KOKX 241124 CCA
AFDOKX

Area Forecast Discussion...CORRECTED
National Weather Service New York NY
724 AM EDT Sun Sep 24 2023

.SYNOPSIS...
The region will remain between high pressure to the north and
Post-Tropical Depression Ophelia low pressure area well to the
south and west today. This low pressure area will slowly move
east northeastward to south of Long Island tonight into Monday.
This will be followed by high pressure building in from
Southeast Canada through mid to late next week.

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Forecast mainly on track with rain showers increasing in
coverage across the region as they move northward. Temperatures
mainly in the upper 50s to lower 60s this morning without much
rise in temperatures expected today.

In the mid levels, the cutoff low becomes an open wave trough as
it moves into western parts of the region late this afternoon.
Ahead of it will be increasing positive vorticity advection,
enhancing vertical lift especially for this afternoon.

Approaching low pressure with tropical remnants of Ophelia along
front south of Long Island will lead to more showers moving in
for today. Isolated thunderstorms in the forecast as well with
elevated instability as shown by forecast model depiction of
slightly negative Showalter Indices across the area. Gusty ENE
flow remains across the region but will be getting remarkably
less than the previous day. Gusts more in the 25 to 30 mph.
Also, with some bulk shear exhibited by forecast models 0-6 km
AGL near 30-35 kt, added in gusty winds for thunderstorms but
thinking upper limit for gusts would be near 35 kt or 40 mph.

Temperatures will stay below normal. Forecast highs only in the
60s.

.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
Another area of showers moves in tonight as the low gets closer
to the area. Models convey good agreement on widespread rain
showers for much of tonight. Rain showers light to moderate but
could be heavy at times.

In the mid levels, the trough axis slows down and remains
within the region tonight and really appears to flatten out for
Monday into Monday night in the forecast model plan views of
500mb height contours. Mid level height gradient weakens going
into Tuesday, allowing steering flow to weaken.

At the surface, low pressure with the tropical remnants of
Ophelia will continue makes its way towards the region but will
stay south of Long Island tonight into Monday. The increasing
lift and vertical moisture will set the stage for more showers
tonight. The low and front shift farther south Monday into
Monday night but with weakening steering flow aloft, the
translational speed of the low and front will be slow.

Layer precipitable waters will be decreasing late tonight into
Monday. This transitions to more of a stratiform rainfall Monday
and eventually the rain will become more confined to the coastal
sections Monday with POPs lowering to chance Monday afternoon
into Monday evening, lower chances to north, higher to the
south. Another cooler than normal day expected Monday as breezy
NE flow continues.

Drying conditions eventually take place from north to south with
rain showers tapering off Monday night into early Tuesday
morning. Low pressure will start moving farther south of Long
Island in response to a little more progression in the upper
levels with the relative increase in upper level westerlies.
High pressure from SE Canada will start to build in from the
north at the surface.

More sunshine is expected Tuesday with high pressure a greater
influence. Mainly dry conditions are expected. Forecast highs
still below normal, mainly in the low to mid 60s for both Monday
and Tuesday.

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A large dome of high pressure over eastern Canada settles south
through the week, building across the Northeast and Mid
Atlantic states. Also, during this time the area will be under a
prolonged period of NE/E flow. There should be a fair amount of
sun during the period. The one caveat to watch is with the
easterly flow perhaps some cloud cover lingering near the coast.

Temperatures during this period will generally be several degrees
below normal, with high in the 60s and lows in the 40s and 50s.
Forecast highs warm to around 70 at weeks end.

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Post-Tropical Depression Ophelia stalled over Eastern Virginia
tracks northeast today as it reaches the Delmarva by this
evening. Mainly widespread IFR will persist through the TAF
period, with only a few pockets of MVFR at times this morning.

Winds remain from the ENE to NE through the TAF period, with more of
a potential backing to true NE late in the TAF period for the 30 hr
terminals. Wind gusts will be mainly 20 to 25 kt, with a few
terminals like KLGA still gusting close to 30 kt at times through
this morning. Wind gusts are likely to start to end this evening,
especially further west across the terminals.

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

LIFR is not expected, but brief LIFR is possible, more so for KEWR
and KTEB this morning. Confidence of occurrence remains too low to
include in the TAFs.

OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY...

Monday: MVFR at times in showers, likely ending from north to south
through the afternoon with improvement to VFR.

Tuesday through Thursday: VFR.

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

.MARINE...
-- Changed Discussion --SCA for all waters until 6PM Monday. There could be occasional
gales on the ocean this morning as well as on Monday. Another
period of gales is forecast Monday night across the ocean but
mainly early and this could be occasional. Due to uncertainty and
occasional frequency thinking, held off on gale watch but do have
the chance for gales on the ocean mentioned in the HWO.

The SCA wind gusts for the non-ocean zones will likely go through
Monday night and into Tuesday for most of the marine zones.
Residual SCA conditions forecast on ocean and some non-ocean
marine zones Tuesday night. Then, mainly SCA conditions on the
ocean mid to late week with below SCA for non- ocean zones.-- End Changed Discussion --

.HYDROLOGY...
-- Changed Discussion --Total forecast rain around 1 to 2 inches through Monday with
locally higher amounts.

Flash flood chances remain low today through tonight. WPC has
excessive rainfall outlook of slight for much of the area. Feel
any flash flood event would be isolated and in those locally
higher amounts especially if they occur in a low-lying or poor
drainage area. Bulk of rain will be today into tonight.
Thunderstorms will be capable of producing locally heavy rain.-- End Changed Discussion --

.TIDES/COASTAL FLOODING...
Water levels for the most part should fall just short of minor
coastal flood benchmarks for today. The exception would be for
Western Peconic Bay as a persistent ENE flow will likely prevent
water levels from coming down in between high tides, thus an
advisory for Peconic Bay in the vicinity of Riverhead has been
issued. Otherwise, no advisories or statements should be needed for
today`s aft / eve high tide cycle. Other than Riverhead / W. Peconic
Bay, this is a change down from the past couple of days.

However, astronomical tides will increase into this week. Thus,
there is a good chance of at least a couple of rounds of minor
coastal flooding. The best chance at minor coastal flood benchmarks
being met is for the Monday and Tuesday PM high tide cycles.
Advisories or statements may be needed for Lower NY / NJ Harbor
(including Staten Island), the south shore bays of Queens, Nassau,
and SW Suffolk, the Western LI Sound shore of Fairfield and
Westchester, and potentially for Peconic Bay if there is not a
change in the current wind direction.

Regarding the beach conditions, high surf, and rip currents,
still expecting high surf along the ocean beaches through early
this evening as well as a high risk of rip currents. Beach
erosion and beach flooding will also be taking place with this
high surf.

Surf height today around 6 to 10 ft this morning, lowering to 5 to 7
ft this afternoon. Swell is from the east direction with 8-9 second
period. Both the high surf advisory and high risk of rip currents
continue through early this evening. Tonight into Monday, waves
further lower getting below high surf advisory criteria but
remaining high enough to keep a high risk of rip currents at the
ocean beaches. The high risk of rip current hazard has been extended
through early evening hours on Monday.

7 ft ocean seas return to the forecast Monday afternoon, mainly mid
to late afternoon. The swell is forecast to be a few less seconds of
period from a general east direction, azimuth-wise about 20
degrees less than the previous day. So, this swell is more ENE
for Monday. SWAN is lower with seas relative to WaveWatch
guidance. Using 7 ft seas with easterly swell, calculated surf
height ranges more in the 4 to 6 ft range, which would be below
high surf advisory thresholds. If seas turn out to the closer to
WaveWatch which indicates ocean seas in the 9 to 11 ft range
for Monday, then the surf height would likewise go up and 7 ft
surf would be a higher chance of occurring.

That being stated, with the high confidence in at least 5 ft ocean
seas Monday, this will easily enable for the development of rip
currents so that high risk of rip currents has been extended
through Monday early evening for the ocean beaches of NYC and
Long Island.

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...High Risk for Rip Currents through Monday evening for NYZ075-080-
081-178-179.
High Surf Advisory until 8 PM EDT this evening for NYZ075-080-
081-178-179.
Coastal Flood Advisory from 5 PM this afternoon to 11 PM EDT
this evening for NYZ079-081.
NJ...None.
MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ331-332-335-
338-340-345-350-353-355.

SYNOPSIS...JM/DW
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...DW
AVIATION...JE
MARINE...JM
HYDROLOGY...JM/DW
TIDES/COASTAL FLOODING...JE/JM