400
FXUS61 KOKX 132001
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
401 PM EDT Thu Jun 13 2024

.SYNOPSIS...
High pressure moves farther out into the Atlantic through
tonight. A cold front approaches Friday and moves across Friday
night. High pressure returns for the weekend before sliding
offshore early next week.

&&

.NEAR TERM /UNTIL 8 AM FRIDAY MORNING/...
High pressure will further weaken tonight and move farther out
east into the Atlantic. After the decrease of the cumulus and
overall mostly clear conditions to start tonight, expecting an
increase in clouds from west to east overnight.

With some low to mid level Q vector convergence noted more so
by the GFS with this not indicated as much with the NAM, have a
slight to low end chance of showers late overnight into early
Friday morning for parts of the southern coastlines covering the
area from coastal CT through coastal NE NJ, NYC and Long Island.
In the mid levels, the models do convey weak positive vorticity
advection on the backside of the mid level ridge traversing the
local region between 2AM and 8AM Friday.

With the southerly flow continuing along the coast and
increasing clouds late, went with more mild low temperatures.
Lows used a combination of NBM and consensus of all guidance,
with values mainly in the mid 60s to near 70.

&&

.SHORT TERM /8 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Upper level trough moves east into the Northeast with associated jet
streak extending from central New England into the Canadian
Maritimes on Friday. The right rear quad of the jet stays in Central
to Northern New England, so northern parts of the forecast region
will have relatively more shear and forcing for more organized
thunderstorms. Around 35-40 kt of 0-6 km AGL shear is forecast
across the interior sections of the region with values closer to 30
kt across Long Island.

For Friday night, the main mid level trough moves across overnight
into early Saturday morning. Models are indicating the upper level
jet streak to expand Friday night, putting the local area closer to
the right rear quadrant of the jet. The 0-6 km AGL shear across the
entire region increases to near 40 kt to 45 kt.

In terms of instability, surface CAPE values are forecast to reach
near 1000 to 1500 J/kg north and west of NYC across the interior
areas, with much less CAPE towards the coast. The surface CAPE
decreases overall to a few hundred J/kg and shifts to be along the
coast for Friday night.

The combination of these factors will provide greater potential for
severe thunderstorms north and west of NYC with less potential for
severe thunderstorms farther east. The SPC has highlighted the
interior areas north and west for a slight risk of severe
thunderstorms with the rest of the forecast region having a marginal
risk of severe thunderstorms.

The structure and form of the showers and thunderstorms will likely
some combination of clusters and a broken squall line. The broken
squall line will be focus of where there could be potentially severe
downbursts of wind. The wind is the main threat with these and to a
lesser extent that of large hail.

Mid level trough approaches Friday with some models indicating a
small wavelength shortwave ahead of the main trough that moves in
for the late afternoon into evening timeframe. At the surface, a
parent low slightly deepens as it moves northeast within Southeast
Canada. Its associated cold front will approach the local region.
There will likely be a pre-frontal trough developing out ahead of
the cold front that will set the stage for initial convection on
Friday afternoon. POPs forecast were taken from a combination of
CAMs that have some variations with individual clusters of
convection but do present a general agreement with a broken line of
convection as well as multiple clusters of convection that move
across north and west of NYC in the early to mid afternoon and then
make their way to the western half of the forecast region late
afternoon into early evening. This late Friday afternoon into early
Friday evening convection will encompass NE NJ, NYC, Lower Hudson
Valley, SW CT and Western Long Island. Thereafter, for mid to late
Friday evening, much of the convection is expected to be across Long
Island and Southern CT. Forecast does have this convection lingering
into the overnight across these areas but thunder chances will
decrease as the night progresses. So, expect mainly showers to
persist along the coast overnight but diminish in coverage going
into early Saturday morning.

High temperatures for Friday are for much of the area from the NBM
where much of the day is expected to be dry with relatively more
sunshine. N&W of NYC covering much of Lower Hudson Valley, interior
NE NJ, and interior SW CT, have 3/4 NBM and 1/4 CONSAll for highs,
which depicts relatively cooler temperatures than using the NBM
alone. Here there are forecast relatively more clouds with showers
and thunderstorms starting earlier in the day. The range of high
temperatures is from the mid 70s to near 80 along much of the
immediate coastline to near 90 for parts of NE NJ and NYC. With
dewpoints mainly in the mid 60s, many locations will have max heat
index values a few degrees higher than the actual temperature.
Still, this gives mostly upper 80s to lower 90s for the max heat
index for much of the Lower Hudson Valley, NE NJ, and NYC.

Low temperatures for Friday night uses a consensus of raw model
data, with a range from the upper 50s to mid 60s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
**Key Point**

* Increasing confidence in a prolonged heat wave mid to late next
  week. Heat indices may approach or exceed 100F at times.

Heights climb on Saturday as the front clears the coast and the
upper trough axis shifts east and offshore. Behind it, a 1024 mb
surface high builds in from the Great Lakes through the weekend as a
subtropical ridge develops and settles over the East, likely
producing the first heat wave of the summer locally.

Ahead of the heat, quite a comfortable June weekend is expected with
abundant sunshine from the nearby high, and afternoon temperatures
within a couple degrees of 80. A relatively dry air mass with dew
points in the 50s should complement this well. Dry conditions are
expected, with some fair weather cu on Saturday, and perhaps
increasing cirrus on Sunday. Sunday morning looks even a bit chilly
in parts of the region with the high pressure nearby, clear skies,
and light flow perhaps allowing efficient cooling overnight yielding
upper 40s across the far interior and the LI Pine Barrens. Utilized
a MAV/MET blend over blended guidance to better capture this.

Ridging then builds late this weekend and early next week with a
590+ dm ridge developing over the Southeast in response to a
vigorous trough swinging onshore the Pacific Northwest. This ridge
amplifies as it settles over the East mid to late next week, and
global ensemble means peg H85 temperatures around 20C much of this
time. This should yield temperatures into the low to mid 90s away
from the coast by next Wednesday, if not Tuesday. Persistent
southerly or southwesterly flow around the offshore surface high
will advect in some higher dew pts, likely into the 60s, leading to
heat indices potentially approaching or exceeding 100F at times.
This could eventually necessitate heat headlines as we move closer.

Given the potential duration of the heat, it`ll be important to take
precautions to protect one`s health, particularly those without
effective cooling and/or adequate hydration. Some heat-sensitive
industries and infrastructure will likely be impacted by the extent
of this heat as well.

&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
VFR through most of the TAF period.

A cold front approaches from the NW late Friday bringing
unsettled weather late Friday into early Saturday morning. Best
chance of TSRA 18-22z Friday KSWF and 20-00z Sat across city
terminals. Heavy rain and gusty winds possible in any TSTM
Friday.

S-SW Winds 10-15kt with gusts to 25kt at the coast continue
into early evening. Tonight, gusts diminish but winds are
expected to remain around 10 kt overnight into Friday morning.
Stronger winds possible in vicinity of stronger TSTMs Friday
afternoon and evening.

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

No unscheduled amendments likely through 18z Friday.

OUTLOOK FOR 18Z FRIDAY THROUGH MONDAY...

18z Friday: MVFR or lower possible in showers/tstms late
afternoon or evening.

Saturday through Monday: VFR.

Tuesday: VFR expected. CHC of MVFR in afternoon SHRA/TSTM mainly
NW of city terminals

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

&&

.MARINE...
More southerly flow this afternoon with gusts expected to 20-25
kt. The gusts will be occasional as warmer air moving in aloft
will limit mixing. So, do not have SCA for any of the forecast
waters as the 25 kt gusts are just expected to be occasional.
Seas on the ocean expected to remain below SCA thresholds and
well below SCA thresholds for non-ocean waters. Wind subside
tonight with wind gusts on Friday to near 20 kt. Winds subside
again Friday night with wind direction eventually becoming more
NW.

Sub SCA conditions are expected on all waters this weekend thru
early next week.

&&

.HYDROLOGY...
For much of the area, there is a marginal risk of flash flooding.
Would expect mostly minor poor drainage flooding in low lying and
urban areas but localized flash flooding cannot be ruled out.
The progressive nature of the thunderstorms is expected to keep
much of any flooding more minor with fast movement of the
thunderstorms. Will just have to monitor potential for multiple
rounds of thunderstorms.

The HREF shows that north and west of NYC is there is potential
(around 10 percent chance) for hourly rain rates of 1 inch per hour
late Friday afternoon into early Friday evening. The chances are
less than 10 percent for the rest of the area for 1 inch per hour
rainfall rates.

The total rainfall amounts from Friday afternoon through Friday
night range from around 0.5 to 0.75 inch to near 1 to 1.5 inches.
NYC is around 1 inch for the storm total rainfall forecast. Locally
higher amounts will be possible.

No hydrological issues are expected this weekend through mid next
week.

&&

.TIDES/COASTAL FLOODING...
There remains a moderate rip current risk this afternoon for the
ocean beaches, and a high risk for most ocean beaches Friday.
Eastern Suffolk beaches are expected to have a moderate rip current
risk on Friday.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...None.

&&

$$

SYNOPSIS...JM/DR
NEAR TERM...JM
SHORT TERM...JM
LONG TERM...DR
AVIATION...IRD
MARINE...JM/DR
HYDROLOGY...JM/DR
TIDES/COASTAL FLOODING...