000
FXUS61 KOKX 061149
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
749 AM EDT Sun Aug 6 2023
.SYNOPSIS...
High pressure builds across the area this morning, then offshore
this afternoon. A frontal system will then impact the area late
tonight through Tuesday. The warm front will move through
late Monday night with the attendant cold front moving through
on Tuesday. Meanwhile, high pressure will gradually build into
the local area from the south and west for mid week. Another
frontal system approaches for Friday and may persist into the
start of next weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Minor adjustments were made with this update, mainly to account
for some cooler temperatures across the interior this morning
and the Pine Barrens region of LI.
High pressure both aloft and at the surface moves across the
area today. This will result in mostly sunny skies with low
humidity and highs right around normal, in the lower to middle
80s for most locations. Metro NJ likely tops out in the upper
80s. A light northerly flow this morning will become onshore
along the coast in the afternoon with interior areas becoming
W/SW as the high builds offshore.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
An amplifying shortwave trough over the Mid/Upper Mississippi
Valley this evening will work its way east into the Ohio Valley
by Monday. This will send a warm front northward toward the
area through Monday night which will be the focus for convective
development. Showers and thunderstorms are forecast to develop
along the boundary this afternoon across SW PA and then work NE
tonight and into the area after midnight. There is deep layer
moisture influx into the region as PWAT values approach 2 inches
tonight, however, there is little if any instability. Decent
omega fields associated with the earlier convection and warm
advection will be the impetus for moderate to heavy rain, a
combination of both convective and stratiform rain. This area
will work SW to NE across the area through the morning hours
Monday with a likely lull in the activity in the afternoon
before the next round. Rainfall amounts for this first round are
forecast to be between 0.50 to 0.75 inches from NYC and points
north and west with lesser amounts to the east. Hourly rainfall
amounts could approach 0.25 inches an hour, but not much higher
with the lack of deep convection.
However, it gets a bit more interesting Monday night as the warm
front gets closer to the region and the airmass further destabilizes
with modest deep-later shear. In addition, with the warm front
nearing the forecast area during the early morning hours, this
will increase the low-level helicity with the possibility of an
isolated tornado threat. The latter of which will depend on how
unstable the low-levels can become right along the warm front to
allow the low-level helicity to be stretched vertically. The
main severe weather threat though is for isolated damaging wind
gusts.
The main concern though is the potential of heavy rainfall
overnight Monday as the airmass looks to destabilize enough to
increase the localized flash flood threat. High PWAT air (around
2 inches) will combine with favorable upper jet dynamics (LFQ)
and lift with the approaching shortwave trough. WPC has placed
much of the are under a Slight Risk for Excessive Rainfall
Monday night into Tuesday morning. There area is likely to see
about 1 to 1 1/2 inches of additional rainfall during this time
with localized higher amounts possible. Once again, highest
amounts are from NYC and points north and west. However, with
the warm front serving as a focus for heavy rainfall, almost
anywhere across the area is under this localized threat. There
is still some uncertainty with how much the airmass will
destabilize in order to enhance rainfall rates. As we get
closer to the event, the CAMs should give us a better idea of
the heavy rainfall potential.
The warm front lifts north of the area Tuesday morning along
with the bulk of the heavy rainfall. However, with the upper
trough moving across the area and a secondary cold front moving
through in the afternoon, scattered convection is likely through
the day. SPC has Marginal Risk for severe weather on Tuesday.
High temperatures on Monday will likely be held down several
degrees due to the cloud cover and morning rainfall. Highs are
forecast to be in the upper 70s to around 80. It will also be
much more humid as dew points climb to around 70. Lows Monday
night will be in the upper 60s to lower 70s, a bit above
normal. Highs rebound on Tuesday into the lower 80s.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Behind the cold front, winds become more westerly and gusty across
the area Tuesday night. Chances for any remaining showers and
thunderstorms Tuesday evening will diminish late evening into
overnight as drier air works into the region. Layer precipitable
waters decrease to near 1.4 to 1.5 inches and eventually down to
near 0.8 to 1 inch by early Wednesday.
High pressure will then build in from the south and west Wednesday
into Wednesday night. Breezy NW winds Wednesday subside Wednesday
night as the center of the high moves in closer to the area. High
pressure moves offshore Thursday allowing for a return to more
southerly flow to develop.
Here is where there is a lot of model uncertainty on the next low
pressure system to impact the region. There are various differences
in the tracks and timing of low pressure areas, associated frontal
boundaries, and their associated areas of rain showers. Forecast has
showers in the Thursday night through Saturday timeframe with
chances of thunderstorms Friday afternoon into early Friday night as
well as Saturday afternoon into early Saturday night.
Layer precipitable waters increase back to near 1.5 to 2 inches
Thursday night into the start of next weekend so some showers and
especially any thunderstorms could result in locally heavy rain.
High temperatures forecast overall stay in the 80s with low
temperatures forecast overall to stay mainly between 60 and 70.
&&
.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
High pressure moves offshore today into tonight with a warm front
approaching late tonight into early Monday.
VFR conditions expected through much of the TAF period. Rain
showers will move in late tonight into Monday morning lowering
conditions to MVFR especially by Monday morning when rain could
be more intense. There will be a slight chance of a
thunderstorm.
NYC terminals and some other coastal terminals have some NE
flow around 5 kt this morning before switching to more
southerly flow during the afternoon. Winds for all terminals
become southerly this afternoon near 10 kt with KSWF having more
WSW flow. Southerly flow decreases to 5-10 kt tonight.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing of wind shift to S-SE today could be a few hours off from
forecast.
Wind speeds could be a few kts higher than forecast for this
afternoon into early this evening.
Timing of showers late in TAF period could be a few hours off from
forecast.
OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY...
Monday-Tuesday: MVFR or lower possible at times. Showers at
times. Lull in shower activity Monday afternoon. Chance of
thunderstorms. SE wind gusts 15-20 kt Monday into Monday
evening. Tuesday SW wind gusts up to around 20 kt.
Tuesday night: Chance of showers and thunderstorms, mainly in the
evening north of NYC and CT terminals with MVFR or lower possible.
Otherwise, mainly VFR. Westerly wind gusts up to around 20 kt.
Wednesday-Thursday: Mainly VFR. Slight chance of showers Thursday
afternoon. Chance of showers Thursday night. A slight chance of
thunderstorms. MVFR possible at times. NW wind gusts around 20 kt
day into evening Wednesday. SW wind gusts 15-20 kt afternoon into
evening Thursday.
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 will remain below SCA criteria as high pressure
remains in control today. An increasing southerly flow ahead of
a frontal system Monday may produce marginal SCA wind gusts and
seas on the ocean late in the day and at night. Winds will then
veer to the SW on Tuesday with gusts approaching SCA criteria
on the ocean, especially east of Fire Island Inlet. Seas on the
ocean build to around 5 ft.
SCA conditions forecast on the ocean Tuesday night into
Wednesday with otherwise mainly sub-SCA conditions forecast on
the other areal waters. Could have some non-ocean waters have 25
kt gusts Tuesday night. All forecast waters are below SCA
thresholds for Wednesday night into Thursday.
&&
.HYDROLOGY...
Multiple rounds of showers and thunderstorms are possible from
late tonight through Tuesday morning. The best chance for
localized to scattered flash flooding will be Monday night into
Tuesday morning. Rainfall amounts of 1 to 2 inches are forecast
across the area with the potential for localized higher amounts.
The WPC has placed most of the area in a slight risk for excessive
rainfall Monday/Monday night.
Heavy rain possible towards end of the week but not confident on the
timing and location of highest rainfall amounts. Too much
uncertainty to determine any flooding risk for showers and
thunderstorms late in the forecast period in the Thursday night
through Saturday time period.
&&
.TIDES/COASTAL FLOODING...
There is a low rip current risk for the NYC beaches today and a
moderate risk elsewhere due to a continued 2-3 ft southerly
swell around 8s. For Monday, there is moderate risk for all
beaches due to a strengthening southerly flow of 10 to 15kt and
building seas.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.
&&
$$
SYNOPSIS...JM/DW
NEAR TERM...DW
SHORT TERM...DW
LONG TERM...JM
AVIATION...JM
MARINE...JM/DW
HYDROLOGY...JM/DW
TIDES/COASTAL FLOODING...