okx-afd on 2024-05-27

542
FXUS61 KOKX 271540
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1140 AM 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 TONIGHT/...
-- Changed Discussion --Minor adjustments with morning updated to reduce pops to low
chance for late morning into early afternoon in wake of initial
band of showers moving east through SE CT this morning. Also
speed up timing of more organized band/s of shower/tstm timing
this aft/eve by a couple of hours.

Morning showers and diurnal heating has helped dense fog to
scour, but patchy fog is likely to continue across LI/S CT
through the day under moist SE flow. Along the immediate ocean,
bay and eastern LI sound front, fog could be dense at times
advecting off the cold waters through the day, until more
organized shower/tstm activity comes in late today.

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

* Additional rounds of showers and embedded thunderstorms are
expected, starting from NYC and points N&W in the early to mid
afternoon, 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: There is a slight risk for severe
thunderstorms, mainly for NYC and points N&W. 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.

Next round of convection this aft/eve will be the ones of
concern for potential of localized flash flooding. There will be
a few other pockets of showers that develop ahead of this line,
but not anticipating them to cause any issues other than brief
moderate to heavy rainfall. A consensus of the latest CAMs
brings the additional lines of heavy showers and thunderstorms
across NYC/NE NJ and the Lower Hudson Valley this afternoon and
early evening, NYC metro late in 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,
strong shear profiles and greater surface based instability to
the west of the region are supportive of organized convection
developing 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 will quickly diminish east of the NYC metro and
Hudson River 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.-- End Changed Discussion --

.SHORT TERM /TUESDAY 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 SUNDAY/...
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 /14Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --A frontal system approaches today and moves across the area tonight.

Mainly MVFR or IFR this morning in stratus and fog. While vsbys have
started to improve at most terminals, the low cigs persist.
Uncertainly with just how much we improve today, especially right
behind a line of showers moving east through the terminals as of
14Z. Expecting a sub VFR day, mainly IFR occasionally improving to
MVFR before declining to IFR or lower late in the day. Rounds of
SHRA and embedded TSRA appears likely this afternoon and into the
first part of tonight. IFR or lower this evening and overnight, then
winds become more westerly and a return to VFR is expected toward
12Z Tue. It may take slightly longer for the far eastern terminals
to see this improvement.

S-SE around 10 kt or less will increase to 10-15G20-25 kt for the
late morning/early afternoon. Winds speeds fall back to 10kt or less
tonight and become more SW or W into early Tuesday morning.

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

Amendments likely today for changing flight categories. Timing of
showers and thunderstorms may be off by 1-2 hours.

OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY...

Tuesday: IFR/MVFR early, improving to VFR. SW winds 10-15G20kt.

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

Friday: Mainly VFR.

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

.MARINE...
-- Changed Discussion --Dense fog advisory remains in effect on all waters, except NY
harbor, through the day with unseasonably moist airmass
advecting over cool waters.

A strengthening SE flow this afternoon will likely result in
wind gusts around 25 kt on the ocean, and possibly south shore
bays/NY harbor this aft/eve . Winds will start to fall below 25
kt, especially after the pre- frontal trough passage and
strongest flow pushes east. 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.-- End Changed Discussion --

.HYDROLOGY...
-- Changed Discussion --Organized bands of showers and thunderstorms are expected to
move across the region from around middle afternoon into 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.

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.-- End Changed Discussion --

.TIDES/COASTAL FLOODING...
-- Changed Discussion --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.-- End Changed Discussion --

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...None.
NY...None.
NJ...None.
MARINE...Dense Fog Advisory until 10 AM EDT this morning for ANZ331-332-
335-338-340-345-350-353-355.
Small Craft Advisory from 6 PM this evening to 6 AM EDT
Tuesday for ANZ350-353.
Small Craft Advisory from 3 PM this afternoon to 6 AM EDT
Tuesday for ANZ355.-- End Changed Discussion --

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