539
FXUS61 KOKX 272023
AFDOKX

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

.SYNOPSIS...
A frontal system will moves through the area 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 /UNTIL 8 AM TUESDAY MORNING/...
Key messages on the shower/thunderstorm threat through late this
evening:

* A few bands of showers and embedded thunderstorms moving east
  across the areas through this evening.

* Flood threat: There is a localized flash flood threat in the
  path of training downpours and thunderstorms into this
  evening. A widespread 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 after
  midnight.

Initial line of leading convection and trailing stratiform rain
will continue to move NE across LI/S CT this late aft. Rainfall
rates of up to 1" in 30 minutes had been experienced with this
line across NYC metro and W LI. This line will continue to
weaken as it moves east.

Focus turns to convection over eastern PA ahead of pre- frontal
trough, which is organizing a bit and moving east into the
watch area. Strong onshore flow, and earlier convection, will
keep surface instability (weak) mainly west of the Hudson River,
but with increasing elevated instability. Approaching shortwave
from Ohio/Pa border, moderate shear profiles and increasing
surface based instability to the west of the region are
supportive of E PA convection continuing to strengthen as it
moves E/NE into western portions of the Tri- State btwn 5 and 8
pm. This continued organization is supported in the CAMs updraft
helicity output (particularly with the better initialized 12z
NSSL WRF). As this activity works into the local Tri-State, 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 with this activity,
mainly west of the Hudson, with the strong low- level
veering/helicity/shear environment.

The severe risk quickly diminishes as this activity moves east
of the Hudson River/NYC due to stronger marine influence after
8-9pm.

At the same time, PWATs are continuing to rise to near 2 inches
late this aft/eve with strengthening S/SW llj, which would
exceed the daily observed max for May 27th per SPC sounding
climatology. Dewpoints in the upper 60s to around 70!. Locally
heavy downpours are occurring with any convection, with NYC
mesonets obs peaking out at 0.2 to 0.4" of rain in 5 minutes.
This easily translates to 2+"/hr rainfall rates, which presents
a localized flash flood threat for any areas that are in the
path of training downpours and tstms. Favored area for the
localized flash flood threat is across the hill terrain N&W of
NYC with better combo of instability and orographics, but also
across NYC metro, W LI, SW CT and LoHud with up to an inch of
rainfall with earlier aft rainfall.

No flood watch, as the flash flood threat continues to be
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 expected to range from 0.75 to 1.25", but
locally 3" amounts possible per high res CAMs and observed
rates. Once again the high end potential would be favored
across the hill terrain N&W of NYC with better combo of
instability and orographics, and more localized elsewhere.

The cold front quickly follows the pre-frontal trough helping to
push the deep moisture and lift eastward with improving conditions
from west to east between 9pm and 1am.

Patchy fog will linger across eastern Long Island and southeast
Connecticut into this evening, finally scouring out after convection
moves through.

&&

.SHORT TERM /8 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Mean troughing continues across the region Tuesday, with initial
shortwave exiting east late tonight and broad trough approaching Tue
afternoon into Tue night.

Atmosphere dries out significantly behind the initial shortwave
and exiting cold front late tonight into Tue AM. A couple of
weak cold fronts moves through the region Tuesday AM and PM.
With limited moisture and W/SW flow, expecting dry conditions
and only scattered aft cu. Gusty offshore flow (25 to 30 mph),
deep mixing, and gradual CAA should allow for temps to rise into
the lower to mid 80s for much of the area. Have leaned towards
NBM ensemble 50th percentile w/ favorable synoptic setup for
heating and NBM deterministic lying near the 25th percentile.

Low pressure continues to track across New England Tuesday night
dragging a PM weak front across the area. Unseasonably mild
conditions continue Tue Night in weak offshore flow.

&&

.LONG TERM /WEDNESDAY 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 /20Z MONDAY THROUGH SATURDAY/...
A frontal system moves through into tonight.

MVFr or lower through tonight as rounds of SHRA and embedded TSRA
moving through this afternoon and into the first part of tonight.
Thunderstorm chances decrease for most terminals by 2Z. Conditions
should decline to IFR or lower across the region this evening,
potentially LIFR overnight in areas of fog development as the rain
tapers by 6Z, before quick improvement to VFR toward 12Z Tue.
Improvement may take up to a couple of hours 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...
Showers and embedded tstms will moves across the water through
around midnight. Dense fog advisory remains in effect for
eastern LI Sound into this evening, with unseasonably moist
airmass advecting over cool waters. Elsewhere with turbulent
flow and slightly better heating over the water, fog potential
will be patchy. Improving cond from west to east after midnight.

SCA SE flow will fall below 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...
Initial line of leading convection and trailing stratiform rain
will continue to move NE across LI/S CT this late aft while
weakening. Focus turns to approaching cluster of heavy
downpours and tstms from E PA/C NJ

Locally heavy downpours are occurring with any convection, with
NYC mesonets obs peaking out at 0.2 to 0.4" of rain in 5
minutes. This easily translates to 2+"/hr rainfall rates, which
presents a localized flash flood threat for any areas that are
in the path of training downpours and tstms. Favored area for
the localized flash flood threat is across the hill terrain N&W
of NYC with better combo of instability and orographics, but
also across NYC metro, W LI, SW CT and LoHud where up to an
inch of rain fell with earlier rainfall.

No flood watch, as the flash flood threat continues to be
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 expected to range from 0.75 to 1.25", but
locally 3" amounts possible per high res CAMs and observed
rates. Once again the high end potential would be favored
across the hill terrain N&W of NYC with better combo of
instability and orographics, and more localized elsewhere.

&&

.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 8 PM EDT Tuesday for ANZ350-353.
     Small Craft Advisory until 8 AM EDT Tuesday for ANZ355.

&&

$$

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