000
FXUS61 KOKX 150016
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
816 PM EDT Mon Aug 14 2023
.SYNOPSIS...
A low pressure system approaches from the southwest, moving
over the region tonight into Tuesday morning, slowly passing
east Tuesday into Tuesday Night. A stalled frontal boundary
remains in the vicinity Wednesday and Wednesday night and may
move back into the region for Thursday. Another cold front
approaches from the west Thursday night and passes through on
Friday. High pressure returns for the weekend. Another cold
front may move through next Monday.
&&
.NEAR TERM /THROUGH TUESDAY/...
-- Changed Discussion --
The forecast is on track with only minor changes needed.
Light rain showers are making their way into the Lower Hudson
Valley and northeast New Jersey. Coverage and intensity should
increase as the evening progresses.
A strong northern stream shortwave/closed low digs through the
Great Lakes into the Ohio Valley tonight into Tuesday, with lead
southern stream MCS enhanced shortwave energy approaching from
the Tennessee/Ohio Valley for tonight. At the surface, a weak
low pressure system over the Ohio Valley, will track northeast
towards the region tonight, with its warm front approaching the
area tonight and potentially lifting into southern portions of
the area late tonight into Tuesday morning.
WSW flow aloft will have strong theta-e advection of an
unseasonably moist airmass into the region (PWAT of 2 1/4" to 2
1/2") ahead of an approaching surface wave and warm front.
Combined with a 25-35kt llj, modest mid-level frontogenetic
forcing, northern edge of elevated instability gradient, and
warm cloud layer up to 15 kft, environment is ripe for
torrential downpours. CAMs indicating a NW to SE translating
line of torrential downpours with embedded convection along the
warm front lifting northeast across the region after midnight
through early Tuesday morning, accentuated by a NE/SW line of
possible surface based convection along immediately ahead of
surface wave and along pre-frontal trough. Exact track of this
surface wave, as is typical, will not be evident until the event
evolves, but appears to cut somewhere across southern portions
of the CWA or just south. This will be the prime area for
moisture convergence and deeper convection, presenting potential
for a more widespread axis of training downpours to the E/NE of
the surface wave, increasing potential for flash flooding.
Another area of potentially longer duration heavy downpours
under favorable frontogenetics and some orographic enhancement
would be across Lower Hud and interior SW CT, to the NW of the
surface wave. Outside of this axis, still an isolated threat for
flash flooding with rainfall rates likely approaching 2"/hr in
any deeper convection, or with any training.
This warm sectored area along the pre-frontal trough in vicinity
of the surface low/warm front would also be favored for an
isolated severe threat with juxtaposition of surface
instability, strong deep layer shear and low level helicity.
This isolated threat appears to be greatest across the NYC/NJ
metro and LI, which has modest potential of becoming warm
sectored. 12z SPC HREF has 10-30% of its ensembles indicating
rotating updrafts across this area. Again, this will need to be
refined as the event unfolds, and the threat could shift
slightly north or south.
As the surface wave slide east, flash flood/severe threat
should come to an end early Tuesday morning from w to e, with
weak cold front likely sinking south of the area. This should
result in a fairly stable airmass across the region Tue, with a
pronounced 750-850mb cap. This could also have a 3-5kft stratus
deck persisting across the region for much of the day. This
will likely keep temps a bit below seasonable levels in the
upper 70s/lower 80s, but still humid in weak onshore flow
regime.-- End Changed Discussion --
&&
.SHORT TERM /TUESDAY NIGHT/...
Deep Ohio Valley upper trough/closed low shears into east Great
Lakes and St Lawrence River Valley Tue Night, with a surface
front likely lingering over or just to the south of the region.
Models indicating potential for another wave to develop along
this front, but likely tracking SE of the region. The forcing
and residual moisture should be enough for few to scattered
showers across the region Tue Eve/Night, with perhaps far
southern and eastern portions of the region being skirted by a
bit more widespread activity Tue Night. Lapse rates may steepen
a bit Tue eve/night, introducing some elevated in stability and
potential for an isolated general thunderstorm as well.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
With the cold front offshore, dry conditions are in the forecast for
Wednesday. However, some deterministic models are bringing
precipitation into the area likely in association with a weak upper
level shortwave to the west that weakens as it crosses the area
during the day. Additionally, the old frontal boundary may remain
close enough to the region to provide some weak lift for some light
showers to develop. At this time, did not add in any POPs, but if
the trend continues, may have to add POPs to later forecasts.
Wednesday night should be dry, if there are any showers, they should
dissipate with the loss of diurnal heating. Better chances for
precipitation on Thursday as the boundary moves closer to the
region. There is some uncertainty with exactly where the frontal
boundary will be, but it looks like the best chances for any showers
and possibly a thunderstorm will be across eastern areas, as they
will be closer to the front.
Thereafter, an upper level trough from the Great Lakes region
approaches for Thursday night which will swing a cold front through
on Friday. This will mean a chance for showers for the entire
forecast area from late Thursday night through Friday morning, with
showers diminishing by Friday afternoon. Dry conditions return for
the weekend and into the beginning of next week with high pressure
building in. Another cold front may move through next Monday, but it
looks to do so dry.
Temperatures are expected to be near normal for this time of year. A
less humid airmass is expected for the weekend, with dew points
dropping to the 50s for much of the region.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
A warm front and associated low pressure approaches, moving
across the region late tonight into Tuesday morning.
Not much change with the 00z TAFs, still looking at VFR
conditions to start, then showers with a warm front should move
across the NYC metros from about 05Z-11Z. IFR conditions
expected with heavier showers during this time frame as well as
a thunderstorm.
Generally a light SE-S flow will continue through the first half
of the night. As the warm front approaches coastal terminals
may back more to the E after midnight.
With the low moving very near or directly across the area Tue
morning, flight categories and wind direction once the band of
heavier showers/tstms moves through are highly uncertain. It is
possible that lingering IFR cigs could hang on for a good deal
of the morning, with light NE-N flow if the warm front remains
just to the south. If it does move through MVFR/VFR conditions
are possible, with SW or WSW flow. For now split the difference
and started off with IFR cigs at many of the terminals,
improving to MVFR by about mid morning, and winds becoming W-NW
behind the departing weak low.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Low confidence of wind direction with warm front and low
pressure passing over or right near the terminals. timing of
precip may be off by an hour or two.
OUTLOOK FOR 00Z WEDNESDAY THROUGH SATURDAY...
Tuesday night: Chance of showers and tstms, mainly in the
evening and especially east of the NYC metros. MVFR or lower
possible.
Wednesday through Thursday afternoon: VFR.
Thursday night: Chance of showers and thunderstorms with MVFR
or lower possible.
Friday: Chance of mainly AM showers and thunderstorms with MVFR
or lower possible. W winds G20kt in the afternoon.
Saturday: VFR.
Detailed information, including hourly TAF wind component
forecasts, can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
Winds and seas remain below SCA levels across the forecast waters
today through Thursday, although ocean seas may build to 4 ft on
Tuesday/Tuesday Night mainly in southerly wind wave.
Winds and waves should remain below SCA criteria from Wednesday
through much of Thursday night. A prolonged south to southwesterly
flow will allow waves to build on the ocean to near 5 ft by late
Thursday night. 5 to 6 ft waves are forecast Friday through Friday
night, with waves slowly diminishing thereafter through Saturday
morning.
&&
.HYDROLOGY...
Basin averaged rainfall of 1.25" to nearly 2" is likely tonight
into Tuesday morning, with localized amounts of 3 to 4"
possible. Much of this is expected to occur in a 3 to 5 hr
period between midnight and 10am from w to e tonight. Rainfall
rates of around 2"/hr possible with any stronger thunderstorms
or training convection. Isolated instances of flash flooding are
likely across the region, with a scattered threat in the
vicinity of the track of a surface wave. This exact axis will
have to be refined as the event unfolds. Headwater guidance is
around 2"/3hr for flashy basins, indicating potential for minor
flooding along quick responding small rivers, stream and creeks.
Based on the above reasoning, and antecedent wet conditions
over the last week, 150-300% above normal, a Flood Watch has
been coordinated for the entire local Tri-State region from 11pm
tonight to 10am Friday.
From Wednesday through the end of the week, no hydrologic impacts
are expected.
&&
.TIDES/COASTAL FLOODING...
There is a moderate risk for the development of rip currents for
Tuesday and Wednesday is expected at all the ocean beaches, with
3 to 4 ft S wind swells, combined with 1 ft long period SE
swells.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from 11 PM EDT this evening through Tuesday
morning for CTZ005>012.
NY...Flood Watch from 11 PM EDT this evening through Tuesday
morning for NYZ067>075-078>081-176>179.
NJ...Flood Watch from 11 PM EDT this evening through Tuesday
morning for NJZ002-004-006-103>108.
MARINE...None.
&&
$$
SYNOPSIS...JP/NV
NEAR TERM...JP/NV
SHORT TERM...NV
LONG TERM...JP
AVIATION...BG
MARINE...JP/NV
HYDROLOGY...JP/NV
TIDES/COASTAL FLOODING...