673
FXUS61 KOKX 121137
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
737 AM EDT Fri Jul 12 2024
.SYNOPSIS...
A stationary front along the east coast, from Maine into the
southeastern states, remains into Saturday as a wave of low
pressure tracks slowly northward from the Carolina coast.
The front washes out just south of the area on Sunday, otherwise,
a thermal trough sets up over the region Monday and Tuesday. A
cold front then approaches from the west on Wednesday, moving
through mid to late next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
The forecast is mainly on track. Increased PoPs slightly over
the next few hours and bumped up total rainfall amounts a little
based on radar. Can`t rule out minor poor/drainage flooding this
morning primarily over NE NJ and NYC.
Generally speaking, rain will eventually become likely across the
entire area today into tonight. A stationary front will remain in
close proximity to the area during this period. A band of high
moisture with PWATS of 2-2.25 inches along the western periphery of
a western Atlantic ridge shifts NW into the vicinity of our western
zones today. The band then stalls/pivots late day into this evening
before beginning to shift back east late tonight. Showers will be
focused along this shifting band as shortwaves aloft provide some
lift, and moisture convergence will be enhanced along the stalled
front with further enhancement inland on a southerly flow. With the
front progged to remain somewhere within the western half of the
forecast area and coincide with enhanced PWATs, flooding concerns
have increased. Thunderstorms will be possible starting late this
morning, and while they are not expected to be severe, they would
still serve to help realize potential rainfall amounts in this moist
airmass.
With the growing threat of flash flooding, a flood watch is now in
effect from this afternoon through Saturday afternoon for NE NJ, NYC
the Lower Hudson Valley, as well as Nassau and Fairfield Counties.
Given flash flood guidance and where rainfall is currently forecast
to be the greatest, did not have confidence to include any areas
east of Fairfield and Nassau Counties. This is in line with WPC`s
ERO slight risk for day 1. Will however buffer the timing to include
all of Saturday afternoon after collaboration with all of the
surrounding offices. See the hydrology section below for more
details.
High temperatures today will be mostly the the middle and upper 80s,
with lows 70-75.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
PWAT axis and heavy rainfall potential shift back east through the
forecast area during the day on Saturday. PoPs lower in the
afternoon, but rain still appears to be likely east of the city by
early to mid afternoon. The frontal boundary doesn`t make much
progress, and may even begin to dissipate. Will need to monitor
trends to see if other areas of southern CT need to be added to the
Flood Watch. The steering flow will strengthen as Saturday wears on,
so this along with current FFG will be mitigating factors for the
flash flooding potential farther east from where the watch currently
exists.
Conditions then dry out Saturday night with dewpoints slowly
lowering. Highs on Saturday in the 80s with mostly 70s for overnight
lows.
Weak high pressure will be in control for Sunday with dry
weather anticipated. 850mb temps increase 17-19C, highest over
western sections. NBM looked reasonable for ambient
temperatures, but probably too high for areas outside of an
onshore flow. W to SW winds will probably help mix out the
surface dewpoints a little during peak heating as the boundary
layer is progged to be dry enough to support. Took a blend of
NBM, CONSALL and superblend for dewpoints. This results in heat
indices reaching at least 95 for portions of the forecast area.
A heat advisory may be needed for these areas as it would be the
start of potentially 4 consecutive days of heat advisory
criteria for parts of the forecast area.
&&
.LONG TERM /MONDAY THROUGH THURSDAY/...
Key points:
* Increasing confidence in an early to mid week heat wave. Afternoon
heat indices may approach or exceed 100F at times. Highest across
urban and interior locations.
* Chance for PM showers and thunderstorms, mainly north and west of
NYC Monday and Tuesday. More widespread chances Wednesday into
Wednesday night ahead of a frontal passage.
No significant changes with this update in the long term. The period
starts hot and humid, and while heights will not be remarkably high,
the forecast area will reside at the southern edge of the westerlies
and result in a deep-layered westerly flow, transporting anomalously
warm air into the region. Ensemble means prog H85 temps around 20C
by Monday, and into the low 20s Tuesday into Wednesday. In addition,
the low-level flow will be more from the SW, which will lessen the
marine influence, especially just inland from the coast. High temps
for much of the area early to mid week will be in the low to mid 90s
with the exception of immediate coastal locations. Upper 90s are
possible in the urban NE NJ corridor, and not out of the question a
few locales touch triple digits. Forecast stayed very close to the
NBM. For dew points however, continued to blend CONSALL in with the
NBM to bring values down a few degrees. With more of westerly flow
than the past heat event, expecting a bit drier air to mix down each
afternoon. This still results in widespread heat indices of 95 to
100 Monday through Wednesday. Heat headlines appear likely, and some
of the interior and urban locations could approach warning criteria
(heat indices of 105F+).
In addition, being at the southern edge of the westerlies will
result in less capping with the potential for diurnally driven
convection Monday and Tuesday afternoon, mainly north and west of
the NYC metro. A more widespread convective event is possible
Wednesday into Wednesday night as a cold front approaches from the
west and PWAT values increase to around 2 inches. Still some spread
in global ensembles, but it appears the fropa should help usher in a
drier and bit cooler regime behind it by late next week.
&&
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
A stationary front remains nearby into Saturday.
Varying categories with SHRA/TSRA at times thru the TAF. First
band of showers pushing inland may lead to MVFR or IFR
cigs/vsbys into mid morning. Embedded thunderstorm possible with
this activity. Thereafter, the boundary shifts farther west,
resulting in continued scattered SHRA at times late this morning
and early afternoon over the NYC metro, NE NJ, and the LoHud.
Eastern terminals (KISP, KBDR, KGON) may remain mostly dry
during this time.
Heavier showers are possible in the afternoon and early evening, and
chances for TSRA increase in this window at NYC terminals, KHPN, and
KSWF, but timing and coverage is fairly uncertain. Another lull
likely develops by the evening hours, before coverage of
showers and possible thunderstorms return overnight, mainly
after 6Z Sat, with conditions potentially lowering toward IFR.
This may persist thru late Sat AM or early afternoon before
gradual improvement and return to VFR.
Light flow early this morning becomes predominantly southerly with
speeds generally increasing to 10 kt. Gusts up to 20 kt will be
possible in the afternoon, mainly for coastal terminals.
Gusts end in the early evening, with 10 kt or less southerly flow
persisting into early Saturday.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing of categorical changes could be off by several hours.
Low confidence in TSRA coverage and timing today and tonight.
Gusts this afternoon may be more occasional.
OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
Saturday: MVFR or lower with showers/thunderstorms early in the day.
Improvement to VFR by afternoon.
Sunday: VFR.
Monday and Tuesday: Mainly VFR. A chance of afternoon into early
evening showers and thunderstorms with MVFR possible, mainly north
and west of NYC terminals.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
Ocean seas remain elevated today into tonight with south to
southeast swells, so the SCA was extended through tonight and may
even need to be extended through Saturday night as conditions will be
marginal. Not enough confidence to extend it that far out yet, but
it at least appears that sub-advisory condition will prevail on
Sunday.
Winds and seas will then largely remain below SCA criteria
early to mid next week. Ocean seas may begin to approach 5 ft
late Wednesday ahead of an approaching front.
&&
.HYDROLOGY...
Rainfall today through Saturday afternoon is expected to range
mostly 1-2 inches in the areas currently with a Flood Watch, with
locally higher amounts possible. Timing of the greatest threat so
far appears to be this afternoon through Saturday morning, but
flooding will still be possible in the afternoon. Additionally,
a threat of minor flooding includes the morning primarily for NE
NJ and NYC. Mostly small stream and minor urban/poor drainage
flooding are anticipated, but isolated to scattered instances of
flash flooding will be possible during this time.
Given an abundantly moist air mass in place, any thunderstorms that
develop early to mid next week will have the potential to produce
locally heavy downpours that result in nuisance flooding,
particularly in urban and poor drainage areas.
&&
.TIDES/COASTAL FLOODING...
There is a high risk of rip current development along all ocean
beaches today through Saturday.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from noon EDT today through Saturday afternoon for
CTZ005-009.
NY...Flood Watch from noon EDT today through Saturday afternoon for
NYZ067>075-176>179.
High Risk for Rip Currents through Saturday evening for NYZ075-080-
081-178-179.
NJ...Flood Watch from noon EDT today through Saturday afternoon for
NJZ002-004-006-103>108.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ350-353-
355.
&&
$$
SYNOPSIS...JC/DR
NEAR TERM...JC
SHORT TERM...JC
LONG TERM...DR
AVIATION...DR/MW
MARINE...JC/DR
HYDROLOGY...JC/DR
TIDES/COASTAL FLOODING...