620
FXUS61 KOKX 251935
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
335 PM EDT Sun Aug 25 2024
.SYNOPSIS...
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High pressure continues to shift offshore this evening
into Monday. A surface trough then develops tonight into Monday
across the area weakening and dissipating. High pressure then builds
north of the region on Tuesday. A warm front moves through Wednesday,
followed by a cold front Wednesday night. High pressure returns
Thursday into Friday. A warm front approaches to begin the
weekend, with a cold front likely to follow later in the
weekend.-- End Changed Discussion --
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Models have more or less come into agreement with a broad upper
trough over the northeast and upper ridging located back to the
west, centered over the Central Plains. A closed upper low
sinking south out of Quebec was noted on the latest GOES-16
6.95um WV loop. Meanwhile, another mid-to-upper level vorticity
max was also noted in the WV imagery rotating through CT. At the
surface, high pressure centered of the western Atlantic
continues to move offshore with a weak sfc trough left in its
wake over the LoHud into western CT this hour.
Clouds and a few developing showers and a single thunderstorm were
noted across NW NJ (Sussex County) where MUCAPE ~1000J/kg via the
SPC mesoanalysis. Into this evening, drier air will continue to
advect in behind this vort feature, essentially limiting any
convective potential for this afternoon/evening.
Lows tonight look similar to last night with upper 50s across the
interior and low to mid 60s elsewhere under SW flow at the
surface..-- End Changed Discussion --
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
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Attention on Monday turns to the severe weather potential,
which has increased across the eastern portion of our area.
The upper low out of Quebec continues to head south through the day
on Monday. Height falls will result as the cold pool becomes more
centered over New England by Monday afternoon. The upper low weakens
as it heads southeast and opens up as a trough by Monday evening
into the overnight. At the surface, a trough develops during the
afternoon as the upper trough approaches. These features will set
the stage for initiation of afternoon showers and thunderstorms, some
of which will be strong to severe, especially for eastern Long
Island and southeast CT on Monday afternoon and evening.
Current convective allowing models show modest instability building
by Monday afternoon along with some bulk shear for organized storms
as the cold pool aloft approaches. The timing of cells moving
south/southeast from southern MA/northern CT along the western
periphery of the upper low varies from about 17-18Z to as late as 20-
21Z. The 12Z HREF mean MUCAPE shows about 1500-2000 J/kg maximized
over southern CT with bulk 0-6km shear values approaching 40 kts.
Model soundings from individual HREF members also show some good
CAPE in the hail growth zone along with a fair amount of DCAPE (500-
1000J/kg), suggesting that severe hail and wind gusts are the main
hazards. In fact, SPC has upgraded portions southern CT and eastern
LI to a slight risk of severe thunderstorms (2 out of 5), with 15%
probabilities of severe winds and large hail. Finally, with modeled
PWATS of less than 2", flash flooding is not a major concern with
this event at this time; see the hydro section below for more
details.
Convection should weaken by early evening as the low/upper trough
pulls away to the northeast. Drier conditions then return late
Monday into Tuesday as upper ridging builds in from the
southwest.-- End Changed Discussion --
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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Weak high pressure will keep things quiet and dry Tuesday
night. On Wednesday a warm front approaches and is progged to
move through. How quickly this happens will determine how
quickly any clouds ahead of the warm front dissipate and move
out. This ultimately will determine how hot things get as a
humid air mass will be in place, especially immediately behind
the warm frontal passage. Heat indices should manage to get into
the 90s for a majority of the area, with dew point readings
mainly around 70. If complete sun breaks out early enough then
heat indices should reach 95 to 100 for the western half of the
area, with some lower 100s possible in urban NE NJ. With the
warm front expect some showers, and possibly a few
thunderstorms. More activity is then possible later in the day
and towards evening just ahead of a cold front. See hydro
section regarding rain and QPF details.
There had been some disagreement among the NWP global guidance in
previous cycles, but now there appears to be more agreement that the
front behaves progressive enough as to get off the coast and clear
the area by Thursday morning. In its wake expect clearing skies and
high pressure to build for the remainder of Thursday into Thursday
night with some lowering of the humidity. Another frontal system
then approaches Friday night, with another round of showers possible
into Saturday with currently chance to slight chance PoPs. At this
time much of Sunday will likely be dry, although a secondary cold
front may approach which could bring a few showers. For now have
opted for chance to slight chance showers with timing highly
uncertain this far out.
After hot and quite humid conditions for Wednesday, temperatures
overall are expected to average near normal thereafter through the
remainder of the long term-- End Changed Discussion --
&&
.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
High pressure centered off the Mid Atlantic coast will continue
to slowly work south and east and away from the area. At the
same time, low pressure will drop south across northern New
England and into the area on Monday.
VFR with SCT CU through tonight, likely becoming BKN on Monday.
An isolated SHRA/TSRA is possible this afternoon with the best
chance north and west of the NYC terminals. For Monday, chances
increase for the eastern terminals, especially late morning
into the afternoon.
Expect a southerly flow this afternoon at 10 kt or less, except
for a local seabreeze enhancement along the immediate coast.
Winds become light S/SW to variable tonight, then light W/SW for
the Monday morning push. Winds will become more southerly at
the coastal terminals around 10 kt in the afternoon. For the
Lower Hudson Valley terminals, KEWR, and KTEB, winds may vary
from W to NW at less than 10 kt. This will depend on the
location of a surface trough on Monday.
NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing of the seabreeze may be off by an hour or so for KEWR and
KTEB this afternoon.
Isolated SHRA/TSRA possible late this afternoon/early this
evening. Low confidence.
OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY...
Monday Afternoon/Evening: VFR. Scattered SHRA/TSRA with MVFR or
lower possible.
Tuesday: VFR.
Wednesday: Chance of MVFR or lower in aft/eve SHRA/TSRA.
Thursday-Friday: Mainly VFR. Chance of aft/eve SHRA/TSRA,
mainly north and west of the NYC terminals.
Detailed information, including hourly TAF wind component
forecasts, can be found at: https:/www.weather.gov/zny/n90
&&
.MARINE...
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Winds and seas are expected to remain below SCA criteria
through Tuesday, as the pressure gradient remains weak across
the region.
Sub small craft conditions prevail into the middle of the week with
ocean seas likely not getting above 3 ft through Wednesday. Marignal
small craft seas then become possible late Thursday and Thursday
night for eastern portions of the ocean.-- End Changed Discussion --
&&
.HYDROLOGY...
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There is chance of nuisance flooding with perhaps an isolated
flash flood threat across southeastern CT and extreme eastern
Long Island Monday afternoon and evening with any thunderstorm
activity. Flash flood guidance from NERFC depicts around 2-2.25"
in an hour or 2- 2.5" in three hours with respect to antecedent
conditions across these areas. With progged PWATS less than 2"
and a somewhat progressive steering flow for storm movement,
widespread flash flooding is not anticipated.
The UFVS-trained model is suggestive of a marginal risk of excessive
rainfall for Wednesday, and this lines up well with WPC`s marginal
risk. At this time the flow appears that it would be progressive
enough to preclude significant or meaningful hydro impacts. However,
minor hydrologic impacts more related to nuisance or minor
urban related flooding cannot be ruled out Wednesday. Rainfall
amounts across northern portions of the area could average close
to an inch, with locally higher amounts possible in association
with any thunderstorms.-- End Changed Discussion --
&&
.TIDES/COASTAL FLOODING...
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A warm front moves through Wednesday, followed by a cold front
Wednesday night. High pressure returns Thursday into Friday. A warm
front approaches to begin the weekend, with a cold front likely to
follow later in the weekend.-- End Changed Discussion --
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.
&&
$$
SYNOPSIS...JE/DBR
NEAR TERM...DBR
SHORT TERM...DBR
LONG TERM...JE
AVIATION...DW
MARINE...JE/DBR
HYDROLOGY...JE/DBR
TIDES/COASTAL FLOODING...