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Area forecast discussion
National Weather Service New York New York
1019 am EST Sat Jan 21 2017

weak high pressure departs later today. Deepening low pressure
approaches from the southwest Sunday and will reach the southern
mid Atlantic region by Monday morning, while high pressure builds
southeast into the Canadian Maritimes. The low will intensify into
a significant coastal storm as it moves up the coast toward the
area Monday through Tuesday. High pressure builds for Wednesday as
the coastal low departs towards New England. A cold front slowly
approaches the area from the west, moving through late Thursday.


Near term /until 6 PM this evening/...
forecast on track with just some minor adjustments to reflect the
latest observations.

Upper ridge builds into the region today. Plenty of low level
moisture trapped underneath inversion through the day today. Weak
sun may not be enough to scour out any of these low level clouds.
Some breaks in the clouds are possible, but generally expect a
mostly cloudy day today.

As such, any clouds could give way to some sunshine, but
generally expect the clouds to predominate.

Temperatures will greatly depend on amount of sunshine that is
realized. Expect high's in the 50s.


Short term /6 PM this evening through 6 PM Sunday/...
through this time frame, ridge axis moves east, as upstream energy
traverses across the mid west and approaches the area Sunday.
Warm air advection commences tonight, with a warm frontal
boundary, extending eastward from mid west low, remaining to the
south of the area through this timeframe.

As the strengthening trough approaches, the low deepens as it
tracks across the Appalachians. With a strong high building toward
the Canadian Maritimes, a tightening pressure gradient is noted
by late Sunday.

Plenty of low level moisture remains in place with light flow
tonight. Low clouds and patchy fog are anticipated tonight. Rain
chances increase from the south Sunday as warm front draws near.

Lows tonight range from the 30s well inland to the mid 40s in and
around NYC. On Sunday, temperatures rise into the 50s, although
increasing easterly flow prevents much more of a rise as the day


Long term /Sunday night through Friday/...
significant coastal storm likely Sunday night into Tuesday with
potential high wind...heavy rain...and coastal impacts.

Have issued a high wind watch for Long Island, coastal CT, New
York City, and some adjacent parts of urban northeast New Jersey
from late Sunday night into much of Monday night. The watch covers
the time frame when wind gusts in those areas will likely exceed
40 mph, with the highest winds capable of meeting high wind
criteria occurring mainly from late morning into the evening.
Siding with slower/stronger 00z NAM/03z sref as the precursor
synoptic pattern is somewhat blocky, the storm very well could
slow down as it closes off and becomes negatively tilted aloft.
Think sustained east winds in the warning area will reach 30-40
mph with gusts 60-65 mph, with the strongest winds across Long
Island and parts of NYC closest to the ocean. Farther north/west,
wind gusts will likely approach or exceed Wind Advisory criteria,
reaching 40-50 mph, with the highest speeds closer to the coast
and in the higher elevations. European model (ecmwf) ensemble wind probabilities
continue to support this general idea as well, with 80-90%
probability of 50+ kt wind gusts over the ocean waters, and 50%
probability just inland.

Slow moving coastal storm passes just south by Tuesday per model
consensus, with a 1 to 3 inch rainfall likely. The heaviest rain
occurs Monday as trough becomes negatively tilted, and abundant
moisture gets pulled northward ahead of the slowing system.
Plenty of Atlantic moisture advects northward ahead of this low,
with the warmer air riding over the cooler air entrenched over
the northeast.

Diabatical cooling is expected, but perhaps not enough for much
wintry weather across the interior.

Gradually improving conditions occur later Tue into Tue night as
the upper low pivots northeast and low pressure tracks up the New
England coast.


Aviation /15z Saturday through Wednesday/...
weak high pressure will move southeast of the area today as a warm
front approaches from the south tonight.

IFR ceilings and visibility will gradually improve to MVFR by 17z.
Otherwise MVFR ceilings will prevail thru this evening. There is a low
chance for VFR conditions if low clouds break.

IFR ceilings and visibility are forecast to redevelop overnight and cont
until at least 15z Sunday.

Winds from 240-260 degrees at 5-10 kt thru evening, then becoming
light and variable overnight.

New York Metro enhanced aviation weather support...

Detailed information, including hourly taf wind component forecasts,
can be found at: http:/www.Weather.Gov/zny/n90

Outlook for 12z Sunday through Wednesday...
Sunday-Sunday night...MVFR or lower in light rain, then moderate
rain at night. NE winds g20-30kt by late day, and g30-40kt later
at night. Low level wind shear possible late Sunday night.
Monday-Monday night...IFR conditions with low level wind shear. Moderate to heavy
rain is expected at all terminals, except perhaps kswf where some
snow or sleet may mix with the rain. East-northeast winds 25-35kt with
g40-55kt, stronger near the coast.
Tuesday-Tuesday night...rain tapering off by the afternoon and with
improving ceilings into the evening. Northwest winds g25-35kt, highest in
the morning.


quiet through Sunday afternoon, then winds should quickly ramp up
to Small Craft Advisory Sunday evening and to gale force later Sunday night. Storm
watch remains in effect for late Sunday night into Monday night.
Easterly wind gusts 50-60 kt expected mainly daytime Mon into Mon
evening on the ocean, and beginning a little bit later Mon morning
on the remaining waters. Strongest winds will be on the ocean, and
even higher gusts 65-70 kt are not out of the question per 00z
NAM, which predicts 950-975 mb winds that strong and either a
well-mixed or moist absolutely unstable layer (maul) to enable
these winds to reach the surface. If forecast trends continue to
increase a hurricane force wind watch might be needed for a
portion of the ocean waters.

Max seas could peak at 20-22 ft on the ocean, 9-12 ft from Orient
Point east, and 8-9 ft on central Long Island Sound, per combo of
wavewatch/nwps guidance and wind/wave climatology.


likelihood of 1 to 3 inches, with locally higher amounts possible
with a coastal storm Sun night into Monday...with heaviest
rainfall Mon aft/eve. If high end rainfall amounts are
realized...this will bring a threat for moderate urban flooding
and minor small stream flooding in NE New Jersey/lower hud valley. This
would be exacerbated by coincidence of high tide with the heavy
rain Mon eve. Rises on larger rivers would be likely...but at this
point the potential for minor flooding appears slight.


Tides/coastal flooding...
a strong coastal storm will likely cause 3 successive high tide
cycles of minor coastal flooding Sunday night into Monday
night...with potential for locally moderate coastal flooding with
the Monday evening high tide. This moderate threat could
linger into the early Tue morning high tide cycle.

An ensemble of guidances is showing potential for surge building to
3 1/2 to 4 1/2 ft by Monday evening.

The highest threat for coastal impacts will be for flood prone
locales along the South Shore bays of Li/NYC...eastern bays of
Li...lower New York/New Jersey Harbor including tidally affected rivers...and
western Li sound.

The other concern will be for widespread dune erosion and localized
washovers at Atlantic Ocean beaches from long period easterly
swells of 15-20+ ft Mon into Tue.


Okx watches/warnings/advisories...
CT...high wind watch from late Sunday night through late Monday
night for ctz009>012.
New York...high wind watch from late Sunday night through late Monday
night for nyz071>075-078>081-176>179.
New Jersey...high wind watch from late Sunday night through late Monday
night for njz006-106-108.
Marine...storm watch from late Sunday night through late Monday night
for anz330-335-338-340-345-350-353-355.


near term...BC/Goodman/pw
short term...Goodman/pw

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