881
FXUS61 KOKX 212359
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
759 PM EDT Fri Jun 21 2024

.SYNOPSIS...
A cold front to the north of the region, slowly retreats back
north as a warm front this weekend. A cold front approaches late
Sunday, moving across Sunday night into Monday, followed by
high pressure on Tuesday. Another frontal system will approach
on Wednesday and move slowly across from Wednesday afternoon
into Thursday. High pressure will return for Thursday night into
Friday.

&&

.NEAR TERM /UNTIL 8 AM SATURDAY MORNING/...
Broken line of weakening convection continues to sag south and
east off the CT coast early this evening. Still an isolated
thunderstorm or two could produce locally heavy downpours and
perhaps a brief wind gust to 40 mph, mainly in southern CT or
the Lower Hudson Valley, but the threat for severe weather is
quickly coming to an end and the Severe Thunderstorm Watch that
was in effect has been cancelled. This weakening convection may
drift south onto Long Island and portions of the NYC metro, but
with limited impact other than passing rain showers. Forecast
remains on track and previous discussion follows.

Region remains on NE edge of southern ridging, with subtle
convectively induced vorts moving through flow. A cold front
over central New England sinks south towards the region this
eve, likely stalling just north of the forecast area late in the
day into night.

Moderate to strong instability development in a weak shear
environment this afternoon to the north of sea breeze boundaries
this afternoon. With trigger from subtle shortwaves aloft, and
focus along sea- breeze boundary across central CT and
approaching pre-frontal trough across NW CT. Expecting both of
these areas of convection to consolidate and sink se across
eastern portions of LoHud and S CT, bringing scattered strong to
severe wet microburst threat in a weak shear and weak mid-level
lapse rate environment, and isolated to scattered flash flood
threat in path of training cells in a 2" PWAT environment. This
activity should weaken after 7-8pm as it sinks se and into more
stable marine layer.

With westerly steering flow, and more stable airmass along the
coast expected convective threat to be isolated for NE NJ, NYC
and LI this evening, with weakening and transition to elevated.
Main threat is for a few pulse strong to severe wet microbursts
across LoHud and southern CT in a weak shear and mid level
lapse rate environment. SPC HREF indicating a low prob for
3"/3hr across southern CT/LoHud, signaling an isolated flash
flood threat from slow moving tstms in a 2" PWAT environment.

Convection will gradually weaken and dissipate late this
evening with loss of daytime instability. Isolated shra/tsra
possible overnight in vicinity of outflow boundaries.
Otherwise, very warm and muggy conditions overnight, with lows
in the lower to mid 70s.

&&

.SHORT TERM /8 AM SATURDAY MORNING THROUGH SUNDAY/...
Upper ridge continues to sink south through the weekend, with
deep layer flow aloft backing from W to SW. At the surface, cold
front retreads north tonight and remains fairly stationary
across central and SE New England through the weekend.

Heat continues to build through the weekend, with 850mb temps
rising into the upper teens on Sat and 20-21C on Sun. Gusty SW
flow and deep mixing will have surface temps similarly
increasing each day away from the coast. High in the mid to
upper 90s likely for NE NJ, NW NYC, and surrounding portions of
LoHuD, with widespread upper 80s to lower 90s for remainder of
the area. A strengthening S/SW flow will limit south coastal LI
and SE CT in the lower to mid 80s each day. High temperatures
on Sunday could touch or break daily records across NYC/NJ
metro.

850mb TDs climb slightly Sat into Sun as well, indicating a
slight upward trends in surface Td`s as well, but still likely
some Td mixout in the afternoon during peak heating. This
expands the threat for 95 to 100 heat index into northern New
London/Middlesex and NW LI for the weekend, continuing from
today. Isolated 105 HI possible for NE NJ and immediate
surroundings Sat and Sun, but too low coverage/confidence for
upgrade to excessive heat at this time. T/Td trends will be
monitored thru the weekend for possible upgrade. Blend of
deterministic NBM and HRRR for T and Td seems to be verifying
well.

Focus for tstms Sat aft/eve looks less clear than today as warm
front pushes farther north into northern New England. Isolated
convective initiation possible along sea- breeze and off higher
terrain to the NW (drifting east) in moderate to strong
instability but still weak shear/mid level lapse rate
environment. More widespread convective development possible
along backdoor cold front moving westward across SE New England,
but this appears to stall east of the area, but could clip far
SE CT. For now, have capped pops at high chance for interior,
to slight/low chance for the coast, based on the above. Isolated
wet microburst potential with any convective development along
and north of these boundaries in moderate to strong instability
and weak shear/mid-level lapse rate environment.

A seemingly better chance for organized convection late Sun
into Sun Eve with lead shortwave ahead of digging Great Lakes
shortwave and pre-frontal trough approaching from the west. This
approaching system will strengthen wind fields and deep layer
shear over the region, likely promoting better organizing of
upstream convection and longer lived updrafts. Question is
timing of this convection into our area. Moderate to strong
instability is likely once again across NYC and pts N&W Sun
afternoon, but late day/evening timing of convection would not
maximize potential. Marginal severe threat from SPC looks
reasonable based on mismatch btwn shear/and peak instability
timing, and strong synoptic S/SW flow disrupting any clear focus
outside of elevation.

Low and localized flash flood threat both days with isolate to
scattered convective coverage on Sat, and likely better forward
progression of convection on Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Key Points:

* Heat wave comes to an end Sunday night-Monday with a cold frontal
  passage.

* One more hot day expected ahead of another frontal system on
  Wednesday.

* A slow moving frontal system could bring locally heavy rainfall
  from late Wednesday into Thursday.

NBM was generally followed, with some adjustments mainly to to
temperatures and dewpoints per 12Z GFS and 00Z ECMWF guidance.

The heat wave should come to an end as an upper trough/closed low
and associated cold front approach the area Sunday night into
Monday. A few tstms with gusty winds possible Sunday evening via pre-
frontal deep layer unidirectional shear (mid layer SW-W flow 35-50
kt) and leftover steep lapse rates from daytime heat. Brief heavy
rain could also be possible with any storms.

Front clears the area daytime Mon, with any 90-plus temps shunted
just south into central NJ, and heat index values close to
actual temps.

Tue should be a bit warmer with high pressure and downslope W-NW
flow in control. High temps will range from 85-90 in most places,
with similar heat index values as afternoon dewpoints should be no
higher than the upper 50s/lower 60s. Wed will be a little warmer and
more humid still, with high temps 90-95 from NYC north/west and the
heat index approaching or just surpassing 95 for one day as
afternoon dewpoints increase to the lower/mid 60s.

A slow moving frontal system should bring an end to this shorter
spell of heat, with chances for tstms from late day Wed into Thu.
More on this in the Hydrology section.

Locally heavy rainfall possible with PW approaching 2 inches and
some potential for training cells along the slow moving frontal
boundary. Attm Fri looks dry with temps near or just above
the seasonal avg.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
High pressure remains across the Western Atlantic as a front
lingers north of the region.

Mainly VFR. Some isolated thunderstorms left over currently,
with mainly just some shower activity. Thunder remains possible
for KSWF, KHPN, KBDR and KGON, likely only until about 01z. For
the other terminals, likely only showers if anything until about
02z. An outflow boundary moved through most terminals and
brought winds around to the north. This will likely only last an
hour or 2 at the most, depending on the terminal. Some patchy
fog/stratus may develop tonight for eastern terminals, but
confidence in this is too low to include in the TAF at this
time.

Winds gradually lighten tonight, with similar flow and speeds
expected Saturday. Showers and thunderstorms are possible again
Saturday afternoon/evening. Thunders will likely be isolated and
confidence was too low to include in the TAF anywhere except
KSWF. PROB30 for SHRA was included elsewhere.

 ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...

Uncertainty in exactly how long winds will stay north this
evening. Regardless, wind speeds will slowly diminish.

Amendments possible for timing and coverage of showers.


OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY...

Saturday Night: Mainly VFR. Showers and thunderstorms possible
in the early evening hours.

Sunday: Mainly VFR. Showers and thunderstorms becoming likely late
day into the night. S-SW wind gusts 15-20 kt.

Monday: Mainly VFR. Chance of showers and thunderstorms, mainly in
the morning.

Tuesday: VFR.

Wednesday: MVFR or lower at times with showers and thunderstorms
possible.

Detailed information, including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90

&&

.MARINE...
Conditions will remain below SCA levels through at least Saturday.
Marginal SCA conditions possible for ocean waters leading to NY
Harbor and surrounding near-shore waters with afternoon coastal
jet development and seas of 3 to 5ft.

Higher confidence in SCA for winds and seas on the ocean water
Saturday Night into Sunday as S-SW flow strengthens. Gusts
up to 30kt possible Sunday aft. Nearshore non- ocean waters may
see advisory gusts conditions as well Sunday aft.

SW flow 20-25 kt on the ocean with a few higher gusts to 30 kt
Sunday night will maintain significant wave heights of 6-8 ft
during that time frame, lowering only to 5-7 ft daytime Mon as
SW flow 15 kt continues. These seas should then gradually
diminish below 5 ft Mon night as a cold front passes and winds
shift offshore.

Conditions fall below small craft late Monday night into
Tuesday morning.

&&

.HYDROLOGY...
Isolated thunderstorms may produce brief heavy downpours that
could lead to brief nuisance flooding, but the threat for more
significant flooding this evening has ended.

Low and localized flash flood threat on Saturday with any slow
moving isolated to scattered tstm activity across interior.

Low flash flood threat late Sunday into Sunday Night with
possible scattered convection development along/ahead of pre-
frontal trough/cold frontal passage.

Another chance for locally heavy rain may come from late Wed into
Thu with another frontal system. PW again increases close to 2
inches and deep layer SW flow could favor training of cells, but
this remains inherently uncertain 5-6 days out.

&&

.TIDES/COASTAL FLOODING...
A moderate rip current risk should continue at the ocean
beaches on Saturday via combo of 3-ft SW wind waves and 2-ft
long period SE swell. A high risk is likely for Sunday as S-SW
flow increases to 20- 25 kt and 5-ft S wind waves increase to
6-8 ft in the afternoon.

Will only mention the high risk in the SRF and HWO and hold off
on rip current statement issuance, to avoid any confusion with
the moderate risk for Saturday.

&&

.CLIMATE...
Here are current record high temperatures thru Sunday...

Saturday, June 22:

NYC: 98(1988)
LGA: 99(1988)
JFK: 94(2012)
EWR: 101(1988)
ISP: 94(2012)
BDR: 93(1949)

Sunday, June 23

NYC: 96(1888)
LGA: 95(1965)
JFK: 94(2010)
EWR: 97(1965)
ISP: 91(1999)
BDR: 91(2010)

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Sunday for CTZ005>009.
NY...Heat Advisory until 8 PM EDT Sunday for NYZ067>075-176-178.
     Heat Advisory from noon Saturday to 8 PM EDT Sunday for NYZ078-
     177.
NJ...Heat Advisory until 8 PM EDT Sunday for NJZ002-004-006-103>108.
MARINE...None.

&&

$$

SYNOPSIS...BG/NV
NEAR TERM...DR/NV
SHORT TERM...NV
LONG TERM...BG
AVIATION...DR/JT
MARINE...BG/NV
HYDROLOGY...BG/NV
TIDES/COASTAL FLOODING...
CLIMATE...DR