Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 032039
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
439 PM EDT Mon Aug 3 2020

.SYNOPSIS...
A surface front will stall near the forecast area tonight.
Isaias will track along this boundary tracking quickly
northeast of the area on Wednesday. Impacts from Tropical Storm
Isaias are possible Tuesday and Tuesday night. A weak low
pressure trough will linger in the wake of Isaias on Wednesday,
then stall to the south from Thursday into Saturday as weak
waves of low pressure move along it. Weak high pressure should
return on Sunday and may last into Monday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A frontal boundary will stall near the area overnight as Isaias
makes its way toward the area. Most models bring in a plume of
moisture well ahead of the system suggesting some sort of
predecessor rain event. There is still some uncertainty between
models as to where and when this sets up, but best chances are
for western sections across northeast New Jersey and the Lower
Hudson Valley, so highest POPs are across these area overnight.

Otherwise, warm and humid conditions expected overnight, with
lows in the upper 60s to middle 70s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
The frontal boundary will stalled near the area Tuesday.
Meanwhile, an upper level low north of the Great Lakes region
will pivot a trough through New England. This will steer Isaias
over the area sometime Tuesday afternoon.

Isaias will likely impact the area starting Tuesday. There is a
tropical storm warning in effect for the entire forecast area.

A Flash Flood Watch continues for much of the forecast area.
Please see the Hydrology section for more information regarding
rainfall.

The highest wind threat with regard to Isaias should correspond to
the eastern semicircle of the storm which places central and western
Long Island, New York City, portions of northeast New Jersey,
and portions of southern Westchester and southwest Connecticut
along the axis of strongest winds. The timing for this looks to
be from late in the day Tuesday into Tuesday evening. Two
positive notes are that the storm is expected to accelerate to
the north and northeast and it is expected to weaken as it does
so. This may limit the duration of impactful winds to some
extent for coastal sections. Sustained winds of around 50 mph
are possible along coastal areas with gusts up to 70 mph.
Generally speaking however, sustained winds of 40 to 50 are
more likely across the forecast area, with gusts 55 to 70 mph.

Additionally, a strengthening low level jet will increase shear
across the area. This may lead to the development of some
tornadoes as Isaias moves approaches and moves through. The
Storm Prediction Center has placed nearly the entire area in a
slight risk for severe storms, with the primary threats being
tornadoes and damaging winds (locally higher wind gusts outside
of the tropical storm force winds expected to occur).

A high rip current risk remains for the ocean beaches Tuesday
through Tuesday night.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
After Isaias passes, will still have to contend with an
anomalously deep closed over southern Canada, maintaining deep layer
SW flow and associated moisture/energy transfer aloft, as well as a
shortwave trough diving in from the Pac NW on the back side of this
low, which does not look to pass east of the area til Sunday
morning. Showers/tstms may fire on Wed invof a lingering sfc trough,
which then sinks to the south Wed night and stalls as weak
disturbances ripple along it. Timing and placement of best rain
chances appears to be Thu night and Fri night, and more so for Long
Island and the NYC metro area and as compared to S CT.

Shortwave ridging aloft should finally move in for Sunday. Uncertain
how long it will persist as model guidance shows the ridge passing
east by Monday, followed by NW flow aloft and passing shortwave
disturbances, a progression which may be a little too quick.

Temps during the period should be just a little above average,
mostly in the 80s, with lower 90s possible in urban NE NJ on Wed and
perhaps again by next Monday. Heat index values High temps combined
with dewpoints in the 60s thru the period should yield heat index
values close to actual temps.

A high rip current risk remains for the ocean beaches Tuesday
through Tuesday night.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
Tropical Storm Isaias will approach from the southeast coast
tonight, and will move over the Mid Atlantic and Northeast on
Tuesday.

VFR through this evening. There is a chance for showers and
thunderstorms to develop ahead of Isaias this evening. Any
storms will be capable of producing strong wind gusts and heavy
downpours which could result in lower visibility. Showers
become likely late tonight into early Tuesday morning with MVFR
to IFR conditions developing.

Winds this afternoon will be from the SW. A few gusts 15-20 kt
are possible into early evening. Winds will gradually turn SE/E
overnight into tomorrow morning. SE winds increase in speed
after 12z tomorrow morning, with gusts in the afternoon 40-60
kt. The strongest winds will across the coastal terminals. As
Isaias moves away to the northeast in the late afternoon, a
quick shift to SW winds is likely.

.OUTLOOK FOR 18Z TUESDAY THROUGH SATURDAY...
.Tuesday afternoon-Tuesday night...Showers and a chance of
thunderstorms with MVFR to IFR conditions. Impacts from Tropical
Storm Isaias likely into the evening. Conditions improving late
Tuesday night.
.Wednesday...VFR with any lingering showers ending.
.Thursday and Friday...VFR.
.Saturday...MVFR possible in SHRA.

&&

.MARINE...
Conditions remain below SCA criteria through tonight.
Conditions deteriorate Tuesday morning with increasing
tropical storm conditions from late Tuesday afternoon into
Tuesday evening across all of the coastal waters based on the
latest forecast track of Isaias. A Tropical Storm Warning is in
effect for all forecast waters. Winds of 45-50 kt will be
possible with gusts up to 60 kt. Isolated gusts of just over 60
kts are possible. Conditions will then improve quickly Tuesday
night from west to east. Wave heights will briefly build to
around or just over 15 ft out on the ocean waters late Tuesday
afternoon into the early evening, then subside fairly quickly
into Tuesday night. Waves of 6 to 10 ft are possible on the
sound waters and 3 to 5 ft across the back bays and Peconic and
Gardiner`s Bays.

Small craft conditions will then ensue on the ocean during the
day on Wednesday due to elevated seas. As early as Wednesday
night even the ocean waters should settle down to below SCA
conditions for Wednesday night into Thursday with some 3-4 ft
seas lingering out on the ocean.

&&

.HYDROLOGY...
There is the potential for more widespread heavy rainfall,
especially Tuesday into at least into the first half of Tuesday
night as Isaias approaches the region. Additionally, the track
of Isaias will need to be monitored to narrow down potential
impacts for minor to moderate river flooding. Confidence in any
moderate river flooding remains low due to rainfall forecast
uncertainty.

A flash flood watch remains for Tuesday through Tuesday night
for NYC, Northeast NJ, and the Lower Hudson Valley where
guidance is lower with rain amounts for flash flood criteria.
This is also closer to the heavier rain axis forecast.

&&

.TIDES/COASTAL FLOODING...
A coastal flood watch has been issued for Lower NY Harbor and
the south shore back bays of western Long Island for the evening
high tide cycle on Thursday.

A strong SE flow ahead Tropical Cyclone Isaias will potentially
result in a surge of 2 1/2 to 3 1/2 ft across the watch area
and 1 to 2 ft elsewhere. This would result in widespread
inundation of 1 to 2 ft with localized values up to 3 ft in the
watch area. There is still uncertainty in the guidance at this
time with preference toward the higher end of the PETSS and
NYHOPS guidance. Should these values continue to increase as the
event nears watches may need to be expanded and eventually
elevated to a warning.

This is appears to be once cycle event with westerly flow
developing on the backside of the system late Tuesday evening.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is
undergoing its final stages of testing, and is operating at full
power.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Tropical Storm Warning for CTZ005>012.
     Flash Flood Watch from Tuesday morning through late Tuesday
     night for CTZ005-006.
     Coastal Flood Warning from 10 PM Tuesday to 2 AM EDT Wednesday
     for CTZ009>012.
NY...Tropical Storm Warning for NYZ067>075-078>081-176>179.
     Coastal Flood Advisory from 9 PM Tuesday to 2 AM EDT Wednesday
     for NYZ072-073-078-079-081-176-177.
     Flash Flood Watch from Tuesday morning through late Tuesday
     night for NYZ067>075-176-178.
     Coastal Flood Warning from 8 PM Tuesday to 1 AM EDT Wednesday
     for NYZ074-075-080-178-179.
     Coastal Flood Warning from 10 PM Tuesday to 2 AM EDT Wednesday
     for NYZ071.
     High Rip Current Risk through Wednesday evening for NYZ075-080-
     081-178-179.
     High Surf Advisory from 8 AM Tuesday to 8 AM EDT Wednesday for
     NYZ080-081-178-179.
NJ...Tropical Storm Warning for NJZ002-004-006-103>108.
     Flash Flood Watch from Tuesday morning through late Tuesday
     night for NJZ002-004-006-103>108.
     Coastal Flood Warning from 8 PM Tuesday to 1 AM EDT Wednesday
     for NJZ006-106-108.
MARINE...Tropical Storm Warning for ANZ330-335-338-340-345-350-353-355.
&&

$$
SYNOPSIS...Goodman/JP
NEAR TERM...JP
SHORT TERM...JP
LONG TERM...Goodman
AVIATION...Fig/DBR
MARINE...Goodman/JP
HYDROLOGY...Fig/Goodman
TIDES/COASTAL FLOODING...
EQUIPMENT...


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