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Forecast Discussion for New York City/Upton, NY

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986
FXUS61 KOKX 271823
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
223 PM EDT Mon May 27 2024

.SYNOPSIS...
A strong frontal system impacts the area through tonight. A
series of reinforcing cold fronts will then move across the
area during the middle of the week. High pressure builds in
Friday into the upcoming weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
Quick update for issuance of SVR TSTM 333 for NYC, LoHud and NE
NJ til 9pm as lines of convection become better organized to
the W/SW of the area and enter the region.

Key messages on the shower/thunderstorm potential this
afternoon into tonight:

* Additional rounds of showers and embedded thunderstorms for
  NYC and points N&W this afternoon into evening, then
  spreading east in the late afternoon and evening.

* Flood threat: There is a localized flash flood threat in the
  path of training downpours and thunderstorms. This threat is
  most pronounced for locations north and west of the NYC metro.
  A broader minor urban/poor drainage flood threat exists for
  the entire area.

* Severe thunderstorm threat: SVR TSTM Watch 333 in effect for
  NYC, LoHud, and NE NJ thru 9 pm. The main concern is from
  damaging wind gusts and hail to around 1" in diameter. An
  isolated and brief tornado is possible as well.

* Conditions will quickly dry out from west to east tonight with the
  majority of the convection offshore by midnight.

Convection coming together over E PA into C/S NJ will move
northeast into western portions of the region through the
remainder of the afternoon into early evening, and Long Island
and Southern Connecticut this late today into this evening.

Strong onshore flow will keep surface instability (weak) mainly
west of the Hudson River, but with increasing elevated
instability. A relatively vigorous approaching shortwave from
Ohio/Pa border, moderate shear profiles and greater surface
based instability to the west of the region are supportive of
convection continuing to strengthen over E PA and C&S NJ and
moving E/NE into western portions of the Tri- State this
afternoon. This organization is supported in the CAMs updraft
helicity output. As this activity works into areas west of the
Hudson River, it will encounter an increasingly more stable
environment, but bring a potential for isolated to scattered
strong to damaging winds before becoming elevated. A non-zero
threat for a brief tornado exists, mainly west of the Hudson,
along any surface based convective lines with the strong low-
level veering/helicity/shear environment.

The severe risk quickly diminishes east of the Hudson River/NYC
due to stronger marine influence.

PWATs should rise to near 2 inches this aft/eve, which would
exceed the daily observed max for May 27th per SPC sounding
climatology. Locally heavy downpours are expected with any
convection, with a localized flash flood threat for any areas
that are in the path of training downpours and tstms. HREF
indicating a 10% ensemble prob of 3"/3hr across areas west of
the Hudson, supportive of an isolated flash threat.

No flood watch, as the flash flood threat is isolated. In
addition, headwater guidance indicating basin average rainfall
amounts of 2" in 6hr, 3" in 12 hr, need for minor flooding of
flashy rivers/streams. This is a low and localized threat.

Storm total rainfall ranges from 0.5 to 1.25 inches, but
locally 3" amounts possible per high res CAMs. This high end
potential would be favored across the hill terrain N&W of NYC
with better combo of instability and orographics.

The cold front quickly follows the pre-frontal trough helping to
push the deep moisture and lift eastward with improving conditions
expected after midnight.

Highs today will only be in the lower to middle 70s. If some
breaks develop west of the city, highs could push closer to 80.
This will have to be watched as it could lead to slightly
higher surface instability. Some fog may linger across eastern
Long Island and southeast Connecticut into the afternoon. The
increasing onshore flow and mixing should prevent the fog from
being dense.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
The deep moisture axis and initial shortwave will continue
pushing offshore Tuesday morning. A larger upper trough will
then linger over the eastern CONUS. Another shortwave within the
trough pushes towards the area through Tuesday afternoon. The
atmosphere dries out significantly behind the lead wave and the
forcing is weak, so will leave the forecast dry. The initial
cold front that moves across late Monday into Monday night
should be offshore, but a surface trough may setup over eastern
Long Island/southeast Connecticut Tuesday. Otherwise, Tuesday
looks mostly sunny and warm. Winds should take on a more
westerly component allowing temperatures to reach the upper 70s
and lower 80s across the region. Some middle 80s are possible
across NYC metro.

Low pressure continues to track across New England Tuesday
night dragging another weak front or surface trough across the
area. Another area of middle level energy dives southeastward
into Wednesday morning and rounds the base of trough into
Wednesday. The trend in the latest guidance has been
weaker/flatter with this system. Models had hinted at a wave of
low pressure developing nearby Wednesday, but chances are a bit
lower. It is possible this system develops Wednesday night or
Thursday. Have lowered PoPs through Wednesday evening and will
not just have slight to low chance late in the day. Temperatures
will be in the 70s across the area.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
An upper level trough remains over the region to start to the
long term with an mid level shortwave moving across the region
on Thursday.

There continue to be differences with the progression of
shortwave energy within the upper trough. The GFS continues to
be more progressive with this feature, while the ECMWF has
remained fairly consistent with a slower, stronger system. The
latter of which reflects a surface low to the south of the area,
For now, will continue to carry just some chance POPS during
this period. Expecting at least a chance of showers areawide
Wednesday night into Thursday. Confidence remains somewhat low
during this time. The shortwave moves away from the region
Thursday night with drier air moving into the area.

Attention then turns to the upper trough closing off just
offshore on Friday. There clearly has been an eastward progression
of this low, which in turn leads to a mainly dry forecast with
surface high pressure building into the area over the weekend.
There are then timing issues with a frontal system progressing
from the west which could bring showers into the region next
Sunday. Right now, expecting a mainly dry weekend. A better
chance of showers returns on Monday.

Highs in the long term will generally remain in the 70s each day,
with the warmest of the day Sunday and Monday, where a few
locations may come close to 80 west of NYC.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
A frontal system moves through into tonight.

Mainly sub VFR day, though brief VFR possible into early
afternoon before consistent MVFR or lower cigs develop across
the local region. Rounds of SHRA and embedded TSRA this
afternoon and into the first part of tonight. Conditions
decline to IFR or lower this evening, potentially LIFR overnight
in areas of fog, before quick improvement to VFR is expected
toward 12Z Tue. Improvement may take slightly longer east of the
city terminals.

A general S or SE flow 10-15ktG20-25kt thru the rest of the
day. Winds speeds lower to 10 kt or less tonight and become
more SW or W into early Tuesday morning. Blustery on Tuesday,
speeds increase toward 15ktG25kt much of the day, generally out
of the west.

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

Amendments expected today for changing flight categories.

Timing of thunder window may be off by 1-2 hours.

OUTLOOK FOR 18Z TUESDAY THROUGH SATURDAY...

Tuesday: VFR. W winds 10-15G20kt.

Tuesday Night: VFR. Light WNW flow.

Wednesday and Thursday: Late Night/AM MVFR/IFR stratus/fog
potential. Otherwise VFR, with chance of aftn SHRA/TSRA.

Friday and Saturday: VFR. Light NW flow.

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

&&

.MARINE...
Dense fog advisory remains in effect for eastern LI Sound,
through the day with unseasonably moist airmass advecting over
cool waters. Elsewhere with turbulent flow over the water, dense
fog potential will be patchy.

A strong SE flow through this afternoon will result in wind
gusts around 25 kt for the south shore bays/NY harbor and ocean
this aft/eve. Winds will start to fall below 25 kt, especially
after the pre- frontal trough passage and strongest flow pushes
east this evening. However, seas are likely to build to around
5 ft this evening into tonight. The SCA continues for the ocean
waters through 10z Tuesday. Conditions should then remain below
SCA levels through Wednesday.

winds and seas will generally remain below SCA criteria for the
middle and end of the week.

&&

.HYDROLOGY...
Organized bands of showers and thunderstorms are expected to
move across the region through this evening.

Locally heavy downpours are expected with any convection,
presenting a localized flash flood threat where the heaviest
rain/training convection ultimately occurs. A more widespread
minor urban/poor drainage flood threat expected for the entire
area.

High-res CAMS indicating hourly rainfall rates as high as 2"/hr
possible in heaviest convection, which is reasonable based on
2" PWATS and warm cloud up to 12-13 kft. SPC HREF signaling a
10% ensemble prob of 3"/3hr across areas west of the Hudson,
indicating this area has the best chance of seeing these higher
rates. This threshold is typically a good signal of isolated to
scattered flash flood potential, although location may need to
be refined. WPC marginal ERO for most of the region, and slight
risk for areas well N&W of NYC, is reasonable based on the above
reasoning.

Storm total rainfall ranges from 0.5 to 1.25 inches, but
locally 3" amounts possible per high res CAMs. This high end
potential would be favored across the hill terrain N&W of NYC
with better combo of instability and orographics.

Headwater guidance indicating basin average rainfall amounts of
2" in 6hr, 3" in 12 hr, needed for minor flooding of flashy
rivers/streams. Overall the potential of minor flooding in
these basins is low and localized.

&&

.TIDES/COASTAL FLOODING...
A strengthening southerly flow ahead of a frontal system will allow
for building surf today with the rip current risk increasing to
moderate in the afternoon. A moderate rip current risk continues on
Tuesday due to 3 to 4 ft seas continuing on the ocean. This is
supported by the latest RCMOS.

Additionally, isolated minor coastal flooding will be possible with
tonight`s high tide cycle. A statement may be needed for the south
shore back bays of Nassau County. Heaviest rain appears to occur
before the time of high tide, which could limit compound flood
impacts.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Dense Fog Advisory until 8 PM EDT this evening for ANZ331-332-
     340.
     Small Craft Advisory until midnight EDT tonight for ANZ332-338-
     340-345.
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ350-353-355.

&&

$$

SYNOPSIS...BC/DS
NEAR TERM...DS/NV
SHORT TERM...DS
LONG TERM...BC
AVIATION...DR
MARINE...BC/DS
HYDROLOGY...BC/DS
TIDES/COASTAL FLOODING...

Previous Forecast Discussions may be found at
NWS New York City/Upton, NY (OKX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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