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Area forecast discussion
National Weather Service New York New York
1042 PM EDT Wed may 24 2017

Synopsis...
low pressure will move slowly east across the area Thursday
night, then move east of the area Friday. Weak high pressure
returns for Saturday. Another frontal system will then impact
the area for the latter half of the Holiday weekend.

&&

Near term /until 6 am Thursday morning/...
clouds, mainly high and mid level, were advancing northward as
seen on satellite, with lower clouds expected after 05z as warm
frontal boundary approaches. Increased cloud cover into Thursday
morning.

Isentropic lift increases ahead of an approaching warm front
resulting in rain developing from SW to NE aft 06z. Rainfall
prior to 12z should be mostly light.

Decided to go with higher categorical pops between 06z and 12z.

For forecasts of coastal flood advisories and statements with
this evening's high tides, read The Tides and coastal flooding
section.

&&

Short term /6 am Thursday morning through Thursday night/...
as an upper low over southeast MO mvs very slowly NE, an upper lvl short
wave rotating arnd its base will become negatively tilted.

Moisture from the Gulf of Mexico and SW Atlantic Ocean will
converge and be tapped from a secondary low developing near Virginia.

Widespread moderate rain of up to 0.50 inch with isolated higher
amounts, more than fcst by the models, is fcst between 12z and
18z Thu, leading to possible minor urban flooding of low lying
and poor drainage areas.

Coastal flood advisories have been issued for Thursday evening's
high tide cycle. And, a coastal Flood Watch has been issued for
parts of the coastal areas for the Thursday evening's high tide
cycle. See The Tides and coastal flooding section.

As the low lifts further north closer to the area, the widespread
moderate rain is forecast to become lighter Thursday afternoon.

Additional rain is forecast Thursday night as the stacked low
passes directly over the local area.

Storm total rainfall is forecast to range from 1.0 to 1.5 inches
with isolated higher amounts through the day Friday.

&&

Long term /Friday through Wednesday/...
a cutoff low lifts NE through the Gulf of Maine Friday,
bringing scattered to numerous showers (se ct). Highs Friday
should be within a few degrees of either side of normal.

Northern stream ridging builds in Friday night-Saturday night,
with associated subsidence keeping things dry, except for maybe
some lingering showers early Friday evening as the upper low
continues to depart. However, a shortwave passing over the top
of the ridge could bring some mid clouds mainly on Saturday.
Lows Friday night should be near to slightly above normal, highs
on Saturday near normal and lows Saturday night a few degrees
above normal.

The northern stream ridge axis slides to the east Sunday,
allowing for shortwaves rotating around the base of a broad
closed low over S central Canada to move across the area from
time to time early next week (unfortunately the timing of
specific shortwaves this far out is problematic at best), at the
same time a combination of weak coastal lows passing to the S
and high pressure building down from southeast Canada should produce
onshore east-southeast flow. So could see some rain/drizzle with any
shortwave given the increase in low level moisture Sunday-Monday
morning, then possibly some showers/thunderstorms late Monday
with the strongest shortwave passing.

Weak ridging builds in from Monday night into Tuesday, followed
by more shortwaves rotating around the S Canada closed low,
which has slid a bit farther east into Hudson Bay/northwest ontario),
Tuesday night and Wednesday - with maybe some more isolated-
scattered showers.

Temperatures should be within a few degrees of either side of
normal Sunday-Monday night, then run above normal Tuesday-
Wednesday.

&&

Aviation /03z Thursday through Monday/...
weak high pressure will be followed by the approach of a low
pressure system late tonight into Thursday.

VFR most of the night with east-southeast winds around 10 kt, increasing
closer to 15 knots overnight. On Thursday, MVFR conds by the
morning push with rain developing, lowering to IFR by the end of
the push. IFR prevails all day with rain. East winds averaging
around 15 knots with gusts 20-25 knots.

Outlook for 00z Friday through Monday...
Thursday night...LIFR/IFR in rain.
Friday...MVFR/IFR possible. Chance of showers.
Saturday...VFR.
Sunday-Monday...MVFR/IFR possible in showers.

&&

Marine...
seas on the outer ocean waters east of Moriches Inlet were up to
6 feet, a few hours ahead of forecast, so increased seas in the
southeast flow ahead of an approaching warm front.

A Small Craft Advisory/Small Craft Advisory remains in effect for Atlantic Ocean
coastal waters through the day Thursday and might need to be
extended for seas through Thursday night.

An Small Craft Advisory was issued for all remaining local coastal waters from 6
am through 6 PM Thursday for east winds of 15 to 25 kt.

As low pressure moves very slowly east across the area through
Thursday night, periods of rain along with isolated
thunderstorms are forecast after 2 am tonight through the day
Thursday.

As the low moves east of the area, winds will shift from the west
at 10-15 kt with gusts to 20 kt on Friday with additional
scattered showers possible.

Small craft level seas should continue on the coastal ocean
waters Friday and Friday night. Otherwise, with a light to
moderate pressure gradient limiting sustained winds to 15 kt or
less Friday- Monday, sub-small craft conditions are forecast
for the waters around Long Island for the Memorial Day weekend.

&&

Hydrology...
1.00" to 1.50" of rain is forecast from 06z Thursday until 00z
Friday. Higher amounts are possible in any thunderstorms that
develop on Thursday. Minor urban and small stream flooding is
possible Thursday.

Another round of rain is possible Sunday night into late
Monday. At this time, it is to soon to specify, what, if any,
hydrologic impact will be experienced from this system.

&&

Tides/coastal flooding...
the Wednesday evening high tide cycle has passed along the South
Shore. Water levels have receded below the minor coastal
flooding benchmarks and additional coastal flooding is no longer
expected. The coastal flood advisories and coastal flood
statements for the South Shore and into coastal; New Jersey for
this evening have been discontinued.

Local and brief minor coastal flooding is possible with
tonight's high tide along southwestern Connecticut and coastal
Westchester County. A coastal flood statement remains.

Astronomical tides are lower for the Thursday morning, however,
a strengthening easterly flow late tonight into Thursday
morning will bring the potential for localized brief and minor
flooding with Thursday mornings high tide.

The primary threat for widespread minor and potentially moderate
coastal flooding still exists for the Thursday night high tide
cycle. How quickly easterly winds begin to weaken Thursday night
will be key to the potential for seeing widespread versus localized
moderate coastal flooding along the southern bays of NYC and western
Li. Along western Li sound, New York/New Jersey Harbor including
Manhattan, and the southern bays of Suffolk County, widespread
minor coastal flooding is likely with less than 1/2 ft of surge
needed in many places to reach minor flood thresholds. Minor
flood thresholds could briefly be touched along the eastern bays
of Li and southeast CT.

The potential for dune erosion looks to be low and localized during
Thursday night high tide.

&&

Okx watches/warnings/advisories...
CT...coastal flood advisory from 10 PM Thursday to 1 am EDT Friday
for ctz009-010.
New York...coastal flood advisory from 7 PM to 10 PM EDT Thursday for
nyz074.
Coastal flood advisory from 10 PM Thursday to 1 am EDT Friday
for nyz071-073-078-176-177.
Coastal flood advisory from 8 PM Thursday to midnight EDT
Thursday night for nyz080.
Coastal Flood Watch Thursday evening for nyz075-178-179.
Coastal flood advisory from 7 PM Thursday to 1 am EDT Friday
for nyz072.
New Jersey...coastal flood advisory from 7 PM to 10 PM EDT Thursday for
njz006-106-108.
Marine...Small Craft Advisory from 6 am to 6 PM EDT Thursday for anz330-
335-338-340-345.
Small Craft Advisory until 6 PM EDT Thursday for anz350-353-
355.

&&

$$
Synopsis...gc
near term...gc/met
short term...gc

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