Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 152012
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
412 PM EDT Tue Oct 15 2019

.SYNOPSIS...
High pressure will continue to retreat farther offshore tonight,
while a strong frontal system approaches on Wednesday. As the
front approaches late in the day, a rapidly deepening coastal
low will form just off the Mid Atlantic coast, tracking near or
just southeast of Long Island Wednesday night. Low pressure
continues to move along the New England coast Thursday and
into the Canadian Maritimes Thursday night. Meanwhile, high
pressure builds to the west. The high moves over the region
Friday, remaining through the weekend. Another frontal system
affects the region Sunday night through Tuesday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
An amplifying upper trough will work across the Great Lakes
tonight, sending a cold front across the Ohio Valley, while
high pressure continues to retreat offshore across the western
Atlantic.

A weak return flow this evening will gradually strengthen
toward daybreak. There is the possibility of some patchy frost
across the interior with light winds and clear skies for much of
the night. Overnight lows will generally be near normal with
the possible exception of the NYC metro, which may be few
degrees above normal. Readings will range from the upper 30s
well north and west, to the lower and mid 50s NYC metro.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Guidance is in good overall agreement with major cyclogenesis
off the Mid Atlantic coast late Wednesday afternoon into the
night. This is in response to an amplifying upper trough
emerging from the Great Lakes and Ohio Valley states, phasing
with a southern branch frontal wave and subtropical moisture.
Where there is some uncertainty, is with the timing and how
explosive the initial development is with the low. The 12Z NAM
continues to be slower and deeper (about 10 mb by 06Z Thu) with
the resultant low. However, the trend is certainly more in line
with the other operational models, and not as deep as previous
runs. This is key for couple of reasons, one for the timing of
the heavy rain, and the other to determine whether the strong
easterly flow will coincide with the time of high tide. The
latter of which raises the issue for potential coastal flooding.
See Coastal Flood section below for additional details.

As for the rainfall, the system is loaded with strong upper
dynamics (negatively tilted upper trough and coupling upper jet
exit and entrance regions) and strong thermal forcing, with the
potential for several inches of rainfall. The heaviest rain
looks to be north and west of the low track, which will
encompass most of the forecast area. Rainfall amounts at this
time look average 2 to 3 inches, with the potential for higher
amounts in banded rain. The one saving grace is that antecedent
conditions have been dry and main stem rivers will likely be
able to handle these amounts. Gridded FFG values for NE NJ are 2
to 2 1/2 inches for 6 hours. Much of this rain occurs in a 6 to
9 hour window from late afternoon/early evening to just after
midnight. Thus, a flash flood watch is in effect for NE NJ.
Elsewhere, there is a lower probability of flash flooding for
urban, poor drainage, and low lying areas.

Ahead of the low, a period of E/SE winds 15 to 20 mph with
gusts up to 30 mph are likely along the coast Wednesday
afternoon/evening. Then in the wake of low pressure, W/NW winds
of 15 to 25 mph and gusts to 40 mph are expected late Wednesday
night.

Both highs and lows Wednesday and Wednesday night will be several
degrees above normal.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
High amplitude, and progressive, flow will continue through the
extended period. One trough with an embedded closed low will be
exiting the east coast Thursday and Thursday night as a ridge builds
across the central United States and well into central Canada. This
ridge moves through the eastern states, and off the coast, Friday
through Saturday night. Meanwhile a series of shortwaves move into
the Pacific northwest, with a stronger wave digging a trough
Saturday night and Sunday. This deep trough will then affect the
region from Sunday night into Tuesday.

For Thursday, strong and gusty winds will prevail in the cold
advection and deep cyclonic flow. Held off on a wind advisory at
this time as will be the fourth period, with low confidence as
sustained winds and gusts will be near advisory levels. Also,
highest winds mostly likely will be across the far eastern zones,
southeastern Connecticut, into the twin forks of Long Island. This
is were best mixing, and strongest low level winds will be. The GFS
had higher winds of 50 to 60 kt 900 to 850 mb, and the ECMWF was in
the 45 to 50 kt range.

With high pressure over the area Friday night, winds will decouple
with nearly clear conditions. This will be ideal radiational cooling
and inland areas, especially the lower Hudson Valley, will see low
temperatures in the mid and upper 30s with areas of frost.

A warm up begins Saturday and continues into early next week. By
Sunday temperatures will be several degrees anomalously above
normal. For Sunday through Tuesday went above guidance temperatures.

There is some uncertainty with the timing of the next system Sunday
night into Tuesday, with the ECMWF developing a wave along the
triple point, and the GFS more delayed with only warm advection
forcing with a warm front developing. Started to bring in
precipitation Sunday night, more in line with the ECMWF.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
High pressure builds offshore tonight into Wednesday.
Meanwhile, a low pressure system approaches the area from the
west on Wednesday and moves across the area Wednesday evening
and Wednesday night.

VFR through mid morning on Wednesday. CLouds will gradually
lower and thicken through the day Wednesday, with MVFR/IFR
conditions around or after 18Z. Rain will move into the area
after 18z, with some of the rain being heavy at times. Timing of
MVFR/IFR conditions may be off by an hour or two.

N-NE between 5-10 kts are beginning to turn towards the SW, and
should remain SW through the evening. Winds tonight then become
light, 5 kts or less, and become more southeasterly. Winds increase
through the day Wednesday with speeds reaching 10-15kt with some
gusts in to the 20kt range.

 ...NY Metro Enhanced Aviation Weather Support...

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

KJFK TAF Comments: VFR Today. No unscheduled amendments
expected.

KLGA TAF Comments: VFR Today. No unscheduled amendments
expected.

KEWR TAF Comments: VFR Today. No unscheduled amendments
expected.

KTEB TAF Comments: VFR Today. No unscheduled amendments
expected.

KHPN TAF Comments: VFR Today. No unscheduled amendments
expected.

KISP TAF Comments: VFR Today. No unscheduled amendments
expected.

.OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY...
.Wednesday...Rain developing. MVFR/IFR by late afternoon and
evening, lingering past midnight at KGON. SE winds G20-25kt.
LLWS also possible along the coast during the evening, mainly at
KISP/KGON. Isolated thunderstorms possible for KISP and KGON
late afternoon/evening.
.Thursday...Possible MVFR with showers. NW winds G25-35kt.
.Friday...VFR. NW winds G20-25kt.
.Saturday...VFR.
.Sunday...VFR.

&&

.MARINE...
A strong frontal system approaches on Wednesday with a developing
coastal low near or just southeast of the waters late in the
afternoon/evening will bring SCA conditions to the area during
the day on Wednesday with SE gusts 25-30kt, then westerly gales
on the backside Wednesday night through Thursday with gusts up
to 40 kt.

A gale warning continues Thursday on all the forecast waters.
Gale force gusts may continue into Thursday evening on the non ocean
waters, and into late Thursday night on the ocean waters.
There is some uncertainty with the timing of diminishing gusts,
therefore the gale warning was not extended into Thursday night.

SCA wind gusts continue through Friday once gusts fall below gale
force levels. Ocean seas are also expected to be below SCA levels by
Friday night.

Tranquil conditions remain on the waters Friday night into the
beginning of next week.

&&

.HYDROLOGY...
A significant rainfall of 1-3 inches is likely Wednesday
afternoon into Wednesday night, with localized swaths of 2-4
inches possible. The bulk of the rainfall is expected in a 6-9
hr period late Wednesday afternoon through Wednesday evening.

Urban, poor drainage, and low lying flooding is expected. There
is a low probability of flash flooding along a few of the fast
responding small rivers and streams in NE NJ and the Lower
Hudson Valley if the higher rainfall amounts are realized.

Additionally, localized flash flooding will also be an issue
for coastal roads if heaviest rain coincides with the Wed night
high tides.

No hydrologic impacts are expected Thursday through the beginning of
next week.

&&

.TIDES/COASTAL FLOODING...
A coastal flood advisory has been issued for SW portions of the
CT coast and southern Westchester in NY due to a strong easterly
flow and gales ahead of deepening coastal low Wednesday night. A
statement is in effect for the much of the coast elsewhere with
the exception of upper portions of NY Harbor.

Tidal departures of generally 2 to 2 1/2 ft above astronomical
are needed for minor flooding during the times of high tide late
Wed Eve into Wed night. The greatest uncertainty with this
event resides around the time of the wind shift from E-SE winds
to W-NW as low pressure moves by. Should the system become more
delayed, the threat for widespread coastal flooding may need to
be expanded.

Additionally, if the heaviest rain coincides with the Wed night
high tide, more widespread flooding could be experienced than
would normally be expected.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO35 (162.55 MHz) remains off the
air.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Coastal Flood Advisory from midnight Wednesday night to 4 AM
     EDT Thursday for CTZ009-010.
NY...Coastal Flood Advisory from midnight Wednesday night to 4 AM
     EDT Thursday for NYZ071.
NJ...Flash Flood Watch from Wednesday afternoon through late
     Wednesday night for NJZ002-004-006-103>108.
MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Wednesday for
     ANZ330-335-338-340-345-350-353-355.
     Gale Warning from 6 PM Wednesday to 6 PM EDT Thursday for
     ANZ330-335-338-340-345-350-353-355.

&&

$$

SYNOPSIS...MET/DW
NEAR TERM...DW
SHORT TERM...DW
LONG TERM...MET
AVIATION...BC
MARINE...MET/DW
HYDROLOGY...MET/DW
TIDES/COASTAL FLOODING...DW/NV
EQUIPMENT...//


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