115
FXUS61 KOKX 061510
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1110 AM EDT Tue Aug 6 2024

.SYNOPSIS...
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A slow moving cold front sags southeast into the area today,
stalling nearby through tonight as a frontal wave tracks along
it. Eventually, the front will push south of the area on
Wednesday as high pressure nudges in from the northwest. The
front then lifts back into the area Thursday into Friday,
followed by a cold frontal passage on Saturday. Tropical
moisture associated with tropical cyclone Debby will interact
with both of these boundaries.

Please refer to the latest official forecast on Debby from the
National Hurricane Center.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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With one wave along the frontal boundary to the north moving
east of the region, updated the probabilities to the timing of
this wave, and then the next into this afternoon as the front
moves south.

A slow-moving cold front will pass through the area and likely
stall this afternoon into tonight across Long Island, NYC metro,
and NE NJ. While this is the general consensus among the
various models available, there is still some uncertainty
regarding how long the front will stall and how far south it
will push before stalling.

Significant tropical moisture is expected to feed along the
frontal boundary, which will increase coverage of the showers
and thunderstorms. Have gone with 70-80%+ POPs for this evening
and early tonight. Widespread PWATs above 2 inches are expected
through this afternoon and into tonight.

Late afternoon into tonight almost all guidance shows warm air
advection and FGEN aloft in tandem with strong vertical velocities
and positive vorticity advection at both 700mb and 500mb. This will
act to enhance rainfall rates in the anomalously moist
environment, leading to scattered instances of flash flooding.
The most likely timing for the highest rainfall rates will be
roughly from 2pm to 2am, but this may change depending on the
front`s progression. The 00Z HREF 10-km neighborhood probability is
showing decent 40-50% chances for >1"/hr rainfall rates for
parts of NE NJ, NYC metro, and Long Island. 1-2 inch/hr rates
are expected in some of the strongest forced showers and
thunderstorms. A Flood Watch will be in effect for the entire
CWA 2PM Today through Noon Wednesday. WPC also has upgraded to
a moderate risk of excessive rainfall for NE NJ, NYC metro, and
western Long Island and maintained their slight risk for the
rest of the CWA.

Thunderstorm coverage may be somewhat scattered at the onset
this afternoon, but the environment should stabilize somewhat
tonight, leading to decreasing thunderstorm chances as we get
into Wednesday. However, there is still a risk for isolated
instances of gusty to damaging wind in some thunderstorms with
00Z CAMs showing the potential for 40-60kt of 0-6km Bulk Shear,
giving some organization to any existing thunderstorms.

Today will be warm and muggy with high humidity and highs in the low-
90s to upper-80s for NE NJ, NYC metro and western Long Island. All
other areas will see highs in the low-80s to upper-70s.
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&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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Eventually, high pressure moving east in Canada will nudge in to our
northwest. This, in turn, may push the stalled front to our south
into the day on Wednesday. This solution has less of a consensus
among models and could lead to some variability in rainfall for
Wednesday depending on the front`s location.

In the early morning hours tomorrow, the stalled frontal
boundary is expected to push south of the CWA, aided by high
pressure nudging in from the northwest. This will lead to
decreasing coverage of showers Wednesday afternoon and evening.

Wednesday night, only isolated shower coverage is expected for
northern portions of the CWA, but southern portions of the CWA
may still see scattered showers due to the closer proximity to
the stalled front to the south. This, however, is subject to
change.

If the front does end up south of the area as expected, then
the highest axis of moisture and forcing will also be fixated to
the south, which may lead to less instances of heavy rainfall
on Wednesday. This would not completely negate flash flood
concerns on Wednesday, but the threat would not be as
significant compared to Tuesday evening and Tuesday night. Its
more likely concerns would be isolated and dependent on the
areas that saw the most rainfall Tuesday evening & night.

With a cold front south of us on Wednesday and plenty of rain-
cooled air and cloud cover, high temperatures will be limited to
the low/mid-70s.
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&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Key Points:

* Potential remains for a moderate to high impact flooding event
  late Thursday into Saturday as multiple frontal systems
  interact with tropical moisture associated with Debby.

* The future track of Debby, and larger scale weather systems
  influencing the storm`s track, will play a big part in how this
  portion of the forecast unfolds. Refer to the latest official
  forecasts from the National Hurricane Center.

Not much change with the 00Z globals as the GFS continues to
linger the circulation of Debby too long over the Southeast and
then shear it out when finally moving northeast late Friday into
the the first half of this weekend. However, the ECMWF/Canadian
while quicker are becoming similar in that the low becomes
absorbed into the mid latitude cold front approaching from the
west. This results in less of defined circulation as the low
works across the area Saturday.

Even before the actual circulation of Debby (no matter what its
classification) approaches, we may have to deal with a tropical
predecessor heavy rainfall event on Friday as a leading warm front
approaches from the south, with good southerly moisture transport
and possibly enhanced lift via weakly coupled jet streaks, one
departing over New England and and another riding up the coast.
In addition, a cold front associated with an amplifying upper
trough across the Great Lakes and Ohio Valley states sends a
strong cold front across the area on Saturday, interacting with
the tropical moisture and producing another potential round of
heavy rain. Deterministic/ensemble QPF`s continue to bear this
out, showing fairly high probabilities of 4+ inches of total
rainfall through the weekend centered over the CWA or in areas
just north.

All the above are still highly uncertain and subject to changes
in the future track and status of Debby as the circulation
eventually comes northward.

Daytime highs should run below normal through Sat, then rebound
closer to normal for Sunday and Monday as rain chances decrease.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
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***Potential High Impact Day***

A slow moving cold front sags southeast into the area today,
stalling nearby through tonight as a frontal wave tracks along
it.

Mainly a VFR forecast through late this morning with occasional
MVFR ceilings this afternoon as showers and thunderstorms
develop and increase in coverage. IFR conditions are then likely
to develop north of the front tonight, especially across the
Lower Hudson Valley and CT terminals, then working south across
the NYC and LI terminals. Airmass stabilizes from north to south
this late this afternoon into tonight. Showers will likely
linger across the area overnight with thunderstorm chances
becoming more limited to the coastal terminals.

Winds will be tricky as the front settles south across the area
today with mainly SW winds to start. A seabreeze is briefly
possible across the NYC and LI terminals before the front passes
through this afternoon. Winds will become E/NE around 10 kt this
afternoon, and then more northerly late tonight. However, some
of the newer guidance is pointing to multiple frontal waves
tracking along the front across the area tonight which could
result in significant variability in wind direction.

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

Amendments are highly likely today for the timing of wind shifts,
flight categories, and showers and thunderstorms.

Chance of IFR tonight.

Winds may vary significantly in direction overnight as multiple
waves of low pressure move across the area. Low confidence in
wind direction.

OUTLOOK FOR 15Z WEDNESDAY THROUGH SATURDAY...

Wednesday and Thursday : MVFR or lower in SHRA.

Friday: MVFR/IFR in SHRA. SE gust 20-25kt possible.

Saturday: MVFR/IFR in RA/SHRA. E to NE gusts 20-25kt possible.

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

.MARINE...
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No changes to the winds and seas at this time.

Sub small craft conditions are anticipated through Tuesday
night. Another period of marginal small craft conditions may
take place on Wednesday for the ocean waters as ocean seas hover
around 4 ft and wind gusts to 20 kt or thereabouts.

There is quite a bit of uncertainty for the end of the week due to
the future track of Debby. Long period southerly swells may start
arriving Thursday into Friday, but at this time seas are kept right
around 4 ft. Seas should increase above 5 ft Fri night, and if the
circulation center of Debby passes to the west, gale force wind
gusts may be possible late Fri night into Sat. The forecast could
significantly change, so please refer to latest forecast information
from the NHC as a starting point.
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&&

.HYDROLOGY...
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A Flood Watch is in effect from 200 PM EDT this afternoon
through Noon Wednesday. WPC has upgraded to a moderate risk of
excessive rainfall for today and tonight for NE NJ, NYC metro,
and western Long Island, and has maintained a slight risk for
the rest of the CWA. Heavy to potentially torrential rainfall
appears likely along a stalled front. This gives us a
heightened potential of localized to scattered instances of
flash flooding with 1 to 2 inch per hour rain rates possible,
especially for the more urban locales. The most likely location
for the highest rain rates will be for southern portions of the
CWA. There remains a chance that locally heavy rainfall
continues into a portion of Wednesday morning before the stalled
front pushes further south of the area.

Heavy rainfall is possible late this week into the weekend, first
from Thu night into Fri as a warm front lifting northward into the
area interacts with tropical moisture well in advance of Debby, then
from Fri night into Sat if the circulation of Debby passes close
by.
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&&

.TIDES/COASTAL FLOODING...
A high rip current risk should continue into this evening per
RCMOS and NWPS guidance. This is due to southerly swells of
around 4 feet. A moderate risk is forecast for Wed as swells
start to diminish.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Flood Watch from 2 PM EDT this afternoon through Wednesday
     morning for CTZ005>012.
NY...Flood Watch from 2 PM EDT this afternoon through Wednesday
     morning for NYZ067>075-078>081-176>179.
     High Risk for Rip Currents until 9 PM EDT this evening for NYZ075-
     080-081-178-179.
NJ...Flood Watch from 2 PM EDT this afternoon through Wednesday
     morning for NJZ002-004-006-103>108.
MARINE...None.
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&&

$$

SYNOPSIS...BR/DW
NEAR TERM...BR/MET
SHORT TERM...BR
LONG TERM...DW
AVIATION...20
MARINE...BR/MET/DW
HYDROLOGY...BR/DW
TIDES/COASTAL FLOODING...