194
FXUS61 KOKX 051140
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
740 AM EDT Mon Aug 5 2024
.SYNOPSIS...
Weak high pressure today gives way to a slow-moving cold front
Tuesday which will eventually stall along or south of our area into
Wednesday. The frontal boundary may briefly sag further south on
Thursday before lifting back into the area for the end of the week.
There is uncertainty with the future track of Tropical Cyclone Debby
and how it may interact with the boundary. Please refer to the
latest official forecast from the National Hurricane Center.
&&
.NEAR TERM /THROUGH TONIGHT/...
Only minor adjustments were made to temperatures and dewpoints
this morning for this update. Otherwise, the forecast remains on
track.
Weak high pressure in place today gradually weakens through the day
as a frontal system approaches from the north. The day will start
off with plenty of sunshine with increasing clouds expected to
increase north to south later in the day as a frontal boundary
approaches. Given ample sunshine and weak high pressure, today
will be a warmer day with highs in the low-90s to upper-80s.
Dewpoints should stay low due to the day starting under a west
wind. Onshore southerly flow returns in the afternoon, but may
not be quick enough to bring high dewpoints in before the peak
heating of the day. Therefore, heat indices should remain below
95 degrees with the exception of parts of NE NJ that may near a
95 degree heat index.
This afternoon and evening we`ll have decent surface heating,
increasing PWATs in the afternoon and evening to 1.6-1.7", and
decent SBCAPE ranging 1000-2,500 J/kg. However, with no major source
of lift, expected only the chance for isolated
showers/thunderstorms. CAMs are showing the chance for 40-45 kt 06km
shear north, west and around NYC which means any storms that are
able to develop should have some organization to them. SPC currently
has parts of the Lower Hudson Valley under Marginal risk with only
the extreme northern portion of Orange county under a Slight Risk.
Expecting mostly cloudy skies to take over tonight with a cold front
continuing to approach closer to our CWA. A few showers and
thunderstorms are possible as the front nears with PWATs increasing,
mainly for northern portions of the CWA.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
A slow-moving cold front with pass over the area on Tuesday and is
expected to stall over the area or south of the area. There is
some uncertainty with regards to where the front stalls since it
mainly hinges on high pressure in Canada and how far south it
nudges the front. This has lead to different solutions among the
CAMs and could greatly influence how much rain we see.
Speaking of rain, this Tuesday to Wednesday timeframe could end up
being a very wet period for us. As the front passes over the region
and begins to stall, enhance tropical moisture feeds along the
boundary, increasing PWAT values Tuesday. PWATs look to peak along a
West to east axis in line with the front Tuesday evening into
Wednesday afternoon. Along the front, 00Z guidance varies, bringing
maximum PWATs anywhere from 2.3 to 2.7 inches. Given the max moving
average PWATs from SPC`s Sounding Climatology page are 2.14", the
2.7" values seem somewhat unrealistic (seen in CAMs like NAM NEST
and HRRR). Regardless, it signals that this cold front could bring
the risk for heavy rainfall. Model soundings also show a decent-
sized warm cloud layer and ideal tall-skinny CAPE profiles for
efficient rainfall. The question remains, however, where the front
stalls. We`ll likely see a period of heavy rainfall Tuesday evening
into Tuesday night as the front passes, but where it stalls on
Wednesday will signal the area at greatest risk for flash flooding.
For now, the models are split. Some guidance shows the front and
axis of highest moisture along Long Island, NYC and NE NJ while
other guidance has higher pressure to our north nudging a little
farther south, leading to the front stalling just south of our area.
WPC currently has us in a Slight Risk for Excessive Rainfall fro
Tuesday. This forecast will become better resolved once more
guidance agrees on the location of the stalled front and all the
CAMs are able to resolve the full event. Either way, showers and
thunderstorms on Tuesday evening and Tuesday night are expected to
have the potential for heavy rainfall which could lead to instances
of flash flooding.
If the front stalls in our area on Wednesday, heavy rainfall may
continue throughout much of the day before tapering off Wednesday
night. However, if the front stalls to our south, we`ll likely only
see scattered showers. Thunderstorms look less likely on Wednesday
due to weak forcing and very little instability.
Wednesday night high pressure to our north is expected to nudge in
further, which should lead to any lingering rain, clearing, with
only isolated showers leftover under partly cloudy skies.
Temperatures during this period will be cooler aided by the rain,
cloud cover, and somewhat lower heights aloft. Highs on Tuesday will
be in the mid-70s to mid-80s. Highs drop into the mid/low-70s on
Wednesday.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
This is a highly complex forecast with much uncertainly due to the
potential interaction of a frontal boundary with tropical moisture
associated with tropical cyclone Debby. In addition, the future
track of Debby will play a big part in how this portion of the
forecast unfolds. Refer to the latest official forecast from the
National Hurricane Center.
The 00Z GFS is an outlier with the future track of Debby once we get
from approximately Wednesday and beyond. A relatively weak shortwave
trough passing to the north during the midweek period provides
enough of a weakness to draw the low slowly north and then northeast
by the weekend, with a track just south and east of the forecast
area. The GFS on the contrary is just far enough south with the
surface low to miss the weakness and retrogrades the low west along
the Gulf Coast states. The GEFS shows quite a bit of spread with its
members, encompassing an area all the way from the eastern Gulf to
the Northeast by the weekend. Bottom line, there are small details
here that can have significant impacts on the forecast. Thus, with
all the uncertainty any deviation from the NBM was subtle.
As this time, the best chance of rain looks to be late Thursday into
Friday with the potential for a significant rainfall event for the
forecast area as tropical moisture overruns a mid latitude frontal
system. Now even with the GFS this becomes more apparent as a
stronger upper trough sends a cold front toward the region for the
weekend, strengthening the frontal zone as the offshore coastal
front returns north as warm front. So the potential for heavy
rainfall arises in both scenarios. There is also quite a bit
difference with the magnitude of the upper trough and cold front for
the weekend.
Daytime highs Thursday and Friday are actually forecast to be
several degrees below normal due to the forecast cloud cover,
chances of rain, and an easterly flow (north of the offshore front).
Temperatures rebound a bit over the weekend as rain chances
decrease, especially for the second half of the weekend.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
Weak high pressure this morning gives way to a cold front dropping
slowly south and east from the Great Lakes. The front passes
through the area late tonight into Tuesday morning, but stalls
close to the area.
Mainly a VFR forecast. Brief MVFR conditions possible late tonight
into Tuesday morning with a chance of showers, possibly a
thunderstorms.
Light and variable winds this morning, becoming S/SW this
afternoon at 10-15kt with a few g15-17kt. Local seabreeze
enhancements expected.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Afternoon sea breeze expected at KJFK and KLGA, within +/- an
hour. Chance of a sea breezes at KEWR and KTEB, but lower
confidence.
OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY...
Tuesday...Mainly VFR with a scattered SHRA/TSRA.
Tuesday Night-Wednesday: MVFR or lower possible in SHRA/TSRA.
Thursday: Mainly VFR. Chance of MVFR or lower in SHRA/TSRA at
night.
Friday: Chance of sub-VFR with SHRA/TSRA.
Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
-- Changed Discussion --
Marginal SCA conditions may continue on the eastern ocean
with a SCA in effect through 15Z. Thereafter, sub-SCA conditions
are expected for the remainder of Tuesday and through Wednesday
night.
There is quite a bit of uncertainty for the end of the week due to
the future track of tropical cyclone Debby. Long period southerly
swells may start arriving Thursday into Friday, but at this time
seas are kept right around 4 ft. However, this could significantly
change. Refer to latest forecast information from the NHC.-- End Changed Discussion --
&&
.HYDROLOGY...
There is the potential for heavy rainfall Tuesday into Wednesday as
a weak area of low pressure moves along a stalled frontal boundary
in the vicinity of the forecast area. However, there remains a good
deal of uncertainty in exactly where the axis of heavy rain will set
up. There will be potential for flash flooding considering the
tropical airmass but too much uncertainty to give precise locations
of higher rainfall amounts. For now, Tuesday afternoon into
Wednesday about 1-2 inches of rain is expected with localized higher
totals possible. WPC has our entire area in a slight risk for
excessive rainfall Tuesday into Wednesday morning.
Another round of heavy rainfall is possible late Thursday into
Saturday as a frontal system potentially interacts with tropical
moisture associated with tropical cyclone Debby. There is even more
uncertainty with this feature.
&&
.TIDES/COASTAL FLOODING...
A high risk of rip currents is expected to continue through at least
Tuesday evening, likely into Tuesday. This is due to southerly
swells of around 4-5 feet.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...High Risk for Rip Currents through Tuesday evening for NYZ075-080-
081-178-179.
NJ...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ350-
353.
&&
$$
SYNOPSIS...BR/DW
NEAR TERM...BR
SHORT TERM...BR
LONG TERM...DW
AVIATION...DW
MARINE...BR/DW
HYDROLOGY...BR/DW
TIDES/COASTAL FLOODING...