000
FXUS61 KOKX 200942
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
542 AM EDT Fri Oct 20 2023
.SYNOPSIS...
A frontal system approaches from the west today. An area of low
pressure develops along the Delmarva Peninsula into tonight and
deepens through Saturday night while tracking into the Gulf of
Maine. The low departs to the northeast Sunday as high pressure
builds in from the west through Monday. The center of this high
pressure approaches Tuesday night and then this area of high
pressure slides out into the Atlantic going into midweek. A weak
cold front moves through Thursday into Thursday night with high
pressure returning thereafter.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
The forecast is generally on track. Extended the likely POPs
into northeastern portions of the Lower Hudson Valley and
southwestern Connecticut given current radar returns.
Showers are expected to increase in coverage this morning,
mainly across northeast New Jersey, New York City, and southern
portions of the Lower Hudson Valley in response stream of
tropical moisture coming in from the south and an incoming
upper level trough moving east from the mid-West and its surface
low over the Great Lakes. There may be some upper level jet
dynamics to enhance the rainfall over these areas, bringing some
moderate rainfall with some of these showers as the stream in
from the south. This feature can be seen in the deterministic
models as well as the CAMs.
As the surface low moves east, it will weaken, but another low
off the Delmarva Peninsula will develop in response to the upper
level trough approaching the coast. This coastal low will
become the primary low. Models continue to show some surface
based CAPE values of a few hundred J/kg, so continue to
highlight a slight chance of thunder.
Southerly flow will bring in slightly above normal temperatures,
but they should still be seasonable, with highs generally in
the middle to upper 60s. Dew points will rise to the 50s to
around 60, allowing for more humid and adding to the
instability and thus supporting the potential for a passing
thunderstorm.-- End Changed Discussion --
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
The coastal low will then move over the area tonight and trek
into the Gulf of Maine by early Saturday night, then trek into
the Canadian Maritimes by daybreak Sunday. Meanwhile, the upper
level trough will continue its approach through Saturday
morning, and as it moves over the area during the afternoon,
there may be a bit of negative tilt to it. However, this will
push the bulk of the heavier precipitation to the east with the
trough axis over the region. However, there are model
differences, and therefore some uncertainty with how heavy the
rain will be on Saturday, but right now, it looks like with
conditions tapering off from southwest to northeast by Saturday
evening.
As the low continues to strengthen, the pressure gradient will
increase across the region, allowing for breezy conditions late
in the day Saturday into Saturday night, with even stronger
winds for Sunday. However, winds look to remain below Wind
Advisory criteria for now. Peak winds look to occur Sunday
afternoon, with gusts to around 35 mph.
As for temperatures, continued seasonable temperatures for
Saturday, with temperatures hard pressed to reach 60 on Sunday
thanks to strong cold advection in association with the
strengthening coastal low.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Subtropical upper level jet extends from Southern US northeastward
out into the Western Atlantic. This jet remains south of the region
through Monday. Then, this jet will move farther north Monday night
through midweek. Over the local region, strong upper level ridging
will take place. The ridge axis moves across on Thursday of next
week before shifting into the Western Atlantic and gradually
weakening thereafter Thursday night into Friday next week.
At the surface, low pressure will be exiting off from the Canadian
Maritimes into the Northern Atlantic Sunday night into Monday.
Across the local region, high pressure will gradually build in from
the west. The center of high pressure traverses near the area Monday
night into Tuesday morning. The high pressure area then slides
southeast of the area out into the Western Atlantic Tuesday through
Tuesday night.
High pressure continues to move farther out into the Atlantic
Wednesday through Wednesday night while also weakening. The next
cold front and associated low pressure system have wide variance in
terms of model timing and placement but took a general approach in
between the GFS and ECMWF, similar to the Canadian models depiction
of the front. The forecast has the cold front approaching Thursday
and perhaps a brief rain shower for locations north and west of NYC
Thursday night, otherwise mainly dry conditions for the region and
just an increase in clouds Thursday into Thursday night.
Temperatures transition from cooler than normal to warmer than
normal during the long term period. Sunday night through Monday
night is the timeframe the cooler than normal temperatures are
forecast. Some frost will be possible north and west of NYC late
Monday night into early Tuesday morning. Near normal high
temperatures are forecast Tuesday. Forecast temperatures are above
normal thereafter for rest of long term. The boost in temperatures
will come from increased low level warm air advection from more SW
flow as high pressure moves offshore.
&&
.AVIATION /10Z FRIDAY THROUGH TUESDAY/...
A wave of low pressure approaches today and eventually moves into
the region tonight.
Initial VFR conditions will lower to MVFR with the development of
rain showers and their increasing coverage going into this morning.
At times, IFR conditions can be expected. Rain showers towards the
latter half of the TAF period could become more intermittent. There
is the possibility of some brief VFR improvement towards late this
afternoon into early this evening.
In addition, there is a low probability for an embedded thunderstorm
from time to time. Due to high uncertainty on exact timing and
placement of thunderstorms, left out of TAFs.
A return to MVFR to potentially IFR conditions is forecast later
tonight when the low center is within the region.
Winds will be SE-S much of the TAF period near 10 kt, but more in
the 10-15 kt range during the day today. An occasional gust to near
20 kt will be possible late this morning into this afternoon. Winds
decrease and eventually become variable direction tonight.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing of categorical changes could be a few hours off from TAF. Low
probability of a thunderstorm but not included in TAF due to low
confidence.
OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY...
Late Tonight through Saturday: MVFR or lower with rain. Improvement
to VFR possible after 18Z Saturday.
Sunday: MVFR possible with CIGS around 3000 ft. W to NW wind gusts
25-30 kt.
Monday: VFR. Gusty NW flow 15-20 kt in the morning.
Tuesday: VFR.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90
&&
.MARINE...
Increasing flow into Saturday as low pressure approaches and
moves through the waters. Westerly wind gusts begin to exceed 25
kts on all waters Saturday afternoon into evening, with ocean
seas building to around 5 ft during this time as well. Seas
continue to increase on the ocean waters to 5 to 9 ft by
Saturday night into Sunday. 3 to 6 ft are possible across the
sound.
The pressure gradient over the area waters continues to
tighten into Sunday, bringing the best chance for gales to the
ocean waters. While the chances for gales are lower on the non-
ocean waters, cannot rule out a few gust to gale force.
Therefore, a Small Craft Advisory has been issued for non-ocean
waters from 2 pm Saturday through 8 pm Sunday, while a Gale
Watch is in effect for the ocean waters from 8 pm Saturday
through 8 pm Sunday, with SCA conditions occurring prior to
this during the day Saturday. There is a chance that the SCA on
the non-ocean waters gets converted to a Gale Warning if winds
end up stronger than what is currently forecast.
Starting Sunday night, gales will be trending down to SCA level wind
gusts on the forecast waters. Overnight Sunday night, non-ocean
waters may very well drop below SCA thresholds for wind gusts.
Outside of some marginal ocean SCA conditions early Monday, overall
mainly below SCA conditions are expected for early to mid week with
high pressure in control.
&&
.HYDROLOGY...
Rainfall between 0.50 (eastern areas) and 1.5 inches (highest
across eastern portions of the Lower Hudson Valley and southwest
Connecticut) is expected from late tonight through Saturday,
with most of the rainfall occurring Friday into Friday night.
Locally heavy downpours with any embedded thunderstorms could
produce nuisance flooding of urban and poor drainage areas.
However, antecedent dry conditions will preclude widespread
flooding.
There are no hydrologic concerns Sunday through next week.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory from 2 PM Saturday to 8 PM EDT Sunday for
ANZ331-332-335-338-340-345.
Small Craft Advisory from 2 PM to 8 PM EDT Saturday for ANZ350-
353-355.
Gale Watch from Saturday evening through Sunday evening for
ANZ350-353-355.
&&
$$
SYNOPSIS...JM/JP
NEAR TERM...JP
SHORT TERM...JP
LONG TERM...JM
AVIATION...JM
MARINE...JM/JP
HYDROLOGY...JM/JP