FXUS61 KOKX 081454

Area Forecast Discussion
National Weather Service New York NY
954 AM EST Fri Dec 8 2023

High pressure will slowly move offshore today through Saturday.
A strong cold front approaches on Sunday and passes through
Sunday night. High pressure then builds in on Monday and remains
in control through the middle of next week.


Despite increasing clouds in the mid layers, temperatures have
risen a few degrees in the last hour, especially across the
metro area. Hourly temperatures are already approaching daily
forecast highs in some of these areas, so increased high
temperatures a couple of degrees or so. Otherwise, forecast is
on track.

High pressure will slowly move offshore today. The core of the high
pressure stays well north and south of the area. The pressure
gradient will remain weak, keeping surface winds quite light,
near or less than 5 kts.

The forecast models have not handled well with the cloud cover and
have underestimated the amount of cloud coverage.

Increased clouds coverage above most model forecasts as a result and
used the lower end of guidance for high temperatures forecast. In
this case, the max temperature forecast was taken from a blend of
MAV and MET guidance, which was relatively lower than NBM. Still
expect a relatively warmer day than the previous, with highs in
the low to mid 40s.


High pressure will continue to slowly move out into the Atlantic
tonight. The pressure gradient remains weak and with more ridging
and even some negative vorticity advection present in the mid
levels, radiational cooling will be more but not totally effective.
Some clouds are expected to linger around tonight but winds are
forecast to decrease and become nearly calm along the coast and for
inland locations will be calm. So, used a blend of MAV and MET MOS
for the forecast low temperatures, which indicated lower
temperatures relative to NBM. Late tonight into early Saturday
morning, put in patchy fog in locations that will have pretty
much calm winds, across the interior. The fog will be possible
as well along the coast but wind speeds will be a little higher
compared to the interior. The fog could possibly get locally
dense across parts of the interior but confidence is low on
this occurring.

For Saturday, the mid level ridging trend ends during the day with a
negative height trend afternoon into early evening. At the surface,
a small drop in the pressure reading is expected as high pressure
continues to move out into the Atlantic. This will result in some
increase to the pressure gradient, driving a more southerly flow
into the area. This will in turn increase the low level warm air
advection. Would also expect clouds to increase as well especially
in the mid to upper levels well ahead of the trough to the west. For
the high temperature forecast, used the NBM 50th percentile. Because
of the recent model underestimation of cloud coverage and winds
still being light (at or less than 10 kts), wanted to select a lower
temperature solution and the NBM 50th percentile was actually
slightly cooler than the deterministic NBM.


A 500mb trough digs in to our west on Sunday, then lifts during the
day Monday with its axis shifting through the forecast area Monday
evening. At the surface, a strong cold front approaches us on Sunday
and passes through during Sunday night. While it's passing through,
an area of low pressure develops along the front in Tennessee or the
Middle Appalachians and passes to our north as is further develops
and strengthens.

Rain chances ramp up through the day with the entire forecast area
likely seeing rain by the end of the afternoon. The rain could be
heavy at times mainly during Sunday night as a strong low level jet
develops over us and combines with deep synoptic lift aloft and an
anomalously moist air mass. Some models continue to show some
elevated instability, so with deep lift, will keep in an isolated
thunderstorm in the forecast. Rain chances continue into Monday even
behind the front as the flow aloft remains cyclonic and we'll be
within the right entrance region of an upper jet streak. Should
precipitation actually occur Monday morning over the higher
elevations well NW of the city, some snowflakes may mix in with
showers. 1.5-2.5" of rainfall is expected Sunday afternoon through
Monday morning. The heaviest rainfall is most likely to occur during
Sunday night. Minor urban/small stream flooding will be possible,
mainly Sunday night - confidence in this is moderate. Cannot
completely rule out flash flooding either, but this is a lower
confidence forecast as chances are low given flash flood guidance
and the progressive nature of the storm system.

Regarding winds for this event, 925mb winds continue to be progged
to reach 60-80kt over roughly the eastern half of the forecast area
Sunday night. Even if a relatively stronger low level inversion were
to be in place during the time that the LLJ moves through, about
half of that speed could potentially reach the surface. The hourly
NBM probabilities for wind gusts greater than 54 mph are at about a
50-80% chance of occurring for the immediate coastlines on Long
Island and southeast Connecticut. These chances are less than 20%
for Manhattan, NE NJ, the lower Hudson Valley and SW CT. Parts of
Queens and Brooklyn are around 20-30% chance of this occurring. Peak
wind gusts may reach wind advisory criteria for some areas along the
coast east of Manhattan given the setup and potential help from heavy
downpours. The current forecast has gusts 40-45mph for coastal areas
and 30-40mph for most inland areas during Sunday night. I used the
NBM 10th percentile for winds in this forecast. The NBM
deterministic seemed too high, but given the last few runs of most
available guidance, they all show gusts at or above this current
forecast (with the exception of the GDPS and RDPS). When this event
falls into the timeframe of some CAMs this will really help in
determining how much of the LLJ will mix down to the surface.

High pressure then builds in through the rest of Monday and remains
in control through Thursday with an extended period of dry weather
and highs generally in the 40s.


High pressure will slowly move offshore through the TAF period.

Mainly VFR conditions are expected. There is the potential for
some MVFR to IFR fog overnight into early Saturday, mainly for
outlying terminals.

Light flow is forecast through the TAF period with wind speeds
below 10 kt. Wind direction will become S-SE this afternoon,
variable tonight, and then SE on Saturday.

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

Wind direction may remain variable 1-3 hours longer into the

MVFR-IFR visibilities possible early Saturday morning.


Saturday: VFR.

Sunday: MVFR or lower in developing rain from west to east
during the day. Slight chance of thunderstorms at night. S
winds increasing with gusts 30 to 40 kt, mainly late day into
night. A few gusts to 45 kt possible, especially at coastal
terminals. LLWS likely with SW winds of around 50-60 kt at 2kft.

Monday: Chance of rain showers early with MVFR possible.
Otherwise, becoming VFR. W-WSW wind gusts 30-40 kt early,
becoming WNW by afternoon with gusts 25-30 kt.

Tuesday: VFR. WSW-WNW gusts 15-20 kt.

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


Below SCA today through Saturday.

Winds and seas should ramp up quickly during Sunday with small craft
conditions quickly going to gales in all likelihood by late in the
day/early evening. Solid gales are expected across all waters Sunday
night, with gales likely lingering into Monday morning for most of
the waters. Gales may continue well in the afternoon on the ocean.
Storm Watch conditions are possible on the eastern ocean waters
based on the new forecast, but confidence in this remains low at
this time. Ocean seas are likely build to 10-15 feet during this
time with waves over 5 ft possible across portions of eastern Long
Island Sound. SCA conds on the ocean for Tuesday as seas remain


There are no hydrologic concerns through Saturday night.

1.50 to 2.50 inches of rain are expected from Sunday afternoon
through Monday morning. The heaviest rainfall is most likely to
occur during Sunday night. Minor urban/small stream flooding
will be possible, mainly Sunday night - confidence in this is
moderate. Cannot completely rule out flash flooding either, but
this is a lower confidence forecast as chances are low given
flash flood guidance and the progressive nature of the storm


With a strengthening southerly flow and increasing astronomical
tides as we approach a new moon, there will be potential for
coastal flooding with the early Monday high tide cycle. This
will be the only high tide of concern for flooding. Westerly
gusts are expected all day Monday and into Monday night, which
should quickly push water levels down. Overall, looks like
mainly a minor coastal flooding event with a very low chance of
moderate coastal flooding.

The southerly flow increases Sunday into Sunday night and then
becomes more westerly Monday. There is a lot of uncertainty in
the surge models with total water level variance in solutions of
up to near 2 to 3 ft.

The timing of the greatest southerly flow appears to coincide
in between the tidal cycles so current total water level
forecasts are getting to minor coastal flooding for parts of the
shorelines along lower NY Harbor and Western LI Sound. The
potential still exists for minor coastal flooding along the
South Shore Bays but for these locations the southerly surge
will be of less duration than farther east and along the
Western Long Island Sound.

ETSS indicates retention of higher surge values in Western Long
Island Sound and north of the South Shore Bays coastlines compared
to the ocean shorelines. This shows the sloshing of water and
areas that do not drain out as well will be potentially more at
risk for coastal flooding. Higher end of Stevens NYHOPS ensemble
surge guidance shows possible localized moderate coastal
flooding for some of the South Shore Bays as well.