discussion on 2023-12-15

000
FXUS61 KOKX 151121
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
621 AM EST Fri Dec 15 2023

.SYNOPSIS...
Strong high pressure remains centered over the Mid Atlantic
today, before being reinforced by a second area of high pressure
building across eastern Canada. High pressure shifts off the
New England coast Saturday night. Low pressure impacts the area
Sunday through Monday. Another low may linger nearby Tuesday and
Wednesday. High pressure then builds in on Thursday.

.NEAR TERM /THROUGH TONIGHT/...
A 1040 mb surface high centered over the Central Appalachians
remains in control today as ridging builds in from the west.

Weak disturbance passing well to the north of the region may allow
for a few 20 to 25 mph gusts early in the day. Otherwise, sunshine
prevails with subsidence aloft limiting mixing and helping to
maintain little in the way of clouds. Temperatures nudge noticeably
upwards from previous days with rising heights and westerly winds.
Highs should manage to top out in the lower and middle 50s, or
about 10 degrees above normal for mid December. Lows tonight range
from the lower 30s across the interior, to the low 40s in the
urban metro.

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
Flattening ridge translates east Saturday, and then offshore
Saturday night. At the surface, additional high pressure builds
in from eastern Canada.

Abundant sunshine persists, and temperatures remain above normal
with another afternoon near 50 for most. Winds gradually veer around
as the high slides off the New England coast Saturday night, setting
up onshore flow ahead of developing low pressure over the Southeast
US. No precipitation is expected through the evening, though cloud
cover quickly increases Saturday night ahead of this next system.

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Low pressure over the Southeast shifts north and deepens with the
help of phasing energy aloft. The center of the low passes over us
or nearby during Monday as it continues to strengthen and head north
towards SE Canada. Rain chances begin Sunday morning with rain then
likely in the afternoon. The rain could be heavy at times Sunday
night into Monday morning as a low level jet interacts with an
anomalously moist air mass. Models show a little instability during
this time as well, so with upward forcing from both the llj and the
deepening low center, a thunderstorm with heavy downpours cannot be
ruled out. See the hydrology section for more details.

As for winds during this event, there`s an increasing chance of at
least advisory-criteria winds - particularly for coastal sections.
925mb winds are progged at 60-80kt along with 50-65kt at 950mb over
coastal sections late Sunday night/early Monday morning. It appears
that the low level inversion will be at least a little weaker than
with this past Sunday-Monday`s storm as temps aloft would be cooler
with SE winds instead of S-SW like the previous system. Thinking
there`s potential for 60-70% of the 925mb winds to mix down to the
surface, especially in the heavier downpours. Might even need to
eventually consider high wind watches over at least eastern LI.

The forecast confidence lowers after Monday night. This is due to
the interaction of a northern stream trough with the departing storm
system. With cyclonic flow aloft, lingering precipitation chances
continue through Tuesday night. Stuck fairly close to NBM. Wednesday
and Thursday look dry with high pressure building in.

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --High pressure remains in place.

VFR. W winds near 10kt, increasing slightly later this morning.
Winds veer NW towards midnight with speeds under 10 kt through the
night.

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

Gusts at KEWR this aftn might be only occasional. Occasional gusts
around 20kt possible at KJFK and KLGA this afternoon. Occasional
gusts 15-18kt possible at KTEB this afternoon.

OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...

Saturday: VFR.

Sat night through Sun morning: MVFR or lower possible in -RA.

Sunday afternoon: Rain likely with MVFR or lower cond. E winds G20kt
NYC metro/coastal terminals.

Sunday night and Monday: IFR in rain, possibly heavy at times.
Isolated thunderstorm possible. SE winds G30-45kt along the coast
and LLWS. Winds shift to S Monday afternoon with G25-30kt, then
shift SW-W and diminish Mon night.

Tuesday: Chance of rain with MVFR or lower cond. NW winds G20kt.-- End Changed Discussion --

.MARINE...
Small Craft Advisory remains in effect for the ocean waters through
this afternoon for westerly gusts around 25 kt and seas of 3 to 6
ft. These conditions subside by this evening. Sub-SCA conditions
then persist on all waters through at least Saturday night.

Winds and seas increase in advance of low pressure approaching from
the south Sunday into Monday. At least gale force winds are probable
over all waters Sunday night through Monday for most spots, and
continuing into Monday evening on the ocean. Cannot rule out gusts
to storm force as well during late Sunday night/early Monday morning
for some of the eastern waters. Wave heights on the ocean peaking at
14-19ft Monday.

Beyond Monday night model guidance spread increases. This leads to a
low confidence win forecast Tuesday through Thursday. At this time,
winds are forecast to remain below 25 kt, but SCA conditions
continue on the ocean waters with elevated wave heights.

.HYDROLOGY...
Chances of rain start as early as Sunday morning, with rain becoming
likely Sunday afternoon and continuing through Monday. The rain is
expected to be moderate, with periods of heavy rain Sunday night
through Monday morning. At this time, a widespread 2 to 3 inches of
rain is expected with locally higher amounts possible. The flash
flooding potential remains low at this time, but minor urban/small
stream flooding is possible. Given the fairly recent heavy rainfall
earlier this week, there is also an elevated threat for river
flooding.

.TIDES/COASTAL FLOODING...
A coastal low has the potential to bring coastal flooding to
the area during the high tide cycles late Sunday night into
Monday. The forcing will be a strengthening S/SE flow that may
bring a prolonged period of gale force gusts. There still remains
some uncertainty with the timing and track of the low which will
be crucial for the extent and magnitude of the event. Right now,
there is a good chance of widespread minor to localized moderate
coastal flooding across Lower NY Harbor and the south shore back
bays of western LI. SW CT also has a good chance of minor coastal
flooding with an isolated potential elsewhere. A limiting factor
will be low astronomical tides being between a full and new moon.
This will be refined as we get closer to the event and there is
better run-to-run continuity of the guidance.

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ350-
353.
Small Craft Advisory until 4 PM EST this afternoon for ANZ355.

SYNOPSIS...JC/DR
NEAR TERM...DR
SHORT TERM...DR
LONG TERM...JC
AVIATION...JC
MARINE...JC/DR
HYDROLOGY...JC/DR
TIDES/COASTAL FLOODING...