discussion on 2023-07-16

000
FXUS61 KOKX 161505
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1105 AM EDT Sun Jul 16 2023

.SYNOPSIS...
-- Changed Discussion --A slow moving cold front will approach from the west today and
passes through the area late tonight. High pressure will then
briefly build across the area on Monday. Unsettled weather is
likely to continue through the rest of the week with the
potential for a series of frontal boundaries.-- End Changed Discussion --

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --Flood Watch remains up for the entire forecast area late through
midnight.

Tornado Watch in remains in effect until 3 PM for eastern
sections of the Lower Hudson Valley, southern CT, and LI.

The heaviest rainfall so far today has occurred with bands
across eastern LI and southern New Haven with rainfall rates of
2 to 3 inches/hour and storms totals up to 5 inches. Additional
activity moving in from the SW may shift the focus for a time
farther west. This will be closely monitored.

Overall, the forecast remains on track with the potential for a
significant flood event (possibly major) through the day today
as a frontal system works into the area ahead of another
shortwave being sent east out of the longwave trough. All the
players are there with record PWAT values of 2.25-2.50 inches,
moderate instability, and enhanced low-level convergence ahead
of the approaching front.

The biggest forecast challenge for this event is to pinpoint
where the heaviest axis of rain will set up across the forecast
area. On average, we are looking a widespread 1 to 3 inch
rainfall with localized amounts 4 to 6 inches. At this time, its
hard to rule out the potential for a few isolated spots
with even higher amounts. Rainfall rates of 1 to 2 inches per
hour remain likely with localized 3+.

WPC maintains the moderate risk of Excessive rainfall across much of
the forecast area.

In addition to the flooding threat, the Storm Prediction Center
has placed much of the area in a slight risk of severe weather
today. The main threat will be isolated tornadoes and strong
gusty winds.

Clouds and rainfall today should result in a cooler day, with highs
around 80.-- End Changed Discussion --

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
Lingering convection in the evening is forecast to work east of
the area during the early morning hours. The cold front is
expected to clear eastern LI/SE CT toward daybreak. Lows are
forecast to be a few cooler, ranging from the upper 60s inland,
to the lower 70s along the coast.

.LONG TERM /MONDAY THROUGH SATURDAY/...
No significant changes have been made to the long term and have
followed the NBM closely for this update.

A persistent longwave upper trough will remain in place over
eastern North American through the time frame, with a series of
shortwave impulses riding through every other day or so this
week with chances for showers/tstms. On Mon we will be in
between impulses and the day should be very warm and somewhat
humid, with highs mostly from the upper 80s to lower 90s, and
afternoon dewpoints from the mid 60s NYC north/west to the lower
70s across Long Island and SE CT. The next chance for organized
convection arrives as the longwave trough axis swings through,
with a marginal risk of excessive rainfall fcst for the Hudson
Valley. Slightly cooler high temps (85-90) and slightly higher
dewpoints (upper 60s/lower 70s) on Tue should yield similar heat
index values to those of Monday.

Max heat index values for the two days should be mostly below 95,
with the possible exception of the urban corridor of NE NJ and some
spots along the north shore of Long Island, with only E Union County
meeting local heat advy criteria of two consecutive days of 95+ heat
index.

Some haze may also be possible Mon night into Tue, per extrapolation
of latest HRRR guidance suggesting some smoke from western Canada
wildfires crossing the Appalachians during that time.

Wed looks like a mostly dry day with shortwave ridging briefly
moving across, then the next organized chance of showers/tstms
should arrive Thu-Fri as the longwave upper trough becomes re-
established. Forecast per NBM currently shows dry conditions for Sat
but confidence in this is low especially east of NYC with
deterministic global models showing a wave of low pressure moving
NNE through the adjacent Atlantic waters.

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --A slow moving cold front will approach from the west today and
passes through the area late tonight. Multiple rounds of showers
and thunderstorms are forecast to precede the front and impact
the terminals into early this evening. Weak high pressure
briefly builds in for Monday.

Conditions will vary between MVFR and IFR this morning with
an overall gradual improvement to MVFR. Occasional VFR
conditions are possible as well this afternoon, but mainly
across the NYC and Lower Hudson Valley terminals. In addition,
any heavy rainfall associated with thunderstorms will produce
brief IFR conditions.
u
A southerly flow is expected through this evening with the
coastal terminals gusting to around 20 kt into this afternoon.
Winds will then diminish this evening, perhaps going light and
variable for a time, before a wind shift to the NW during the
early morning hours.

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

Ceilings will vary some IFR and MVFR heading into early this
afternoon, then between MVFR and VFR this afternoon.

Amendments are likely for the timing of showers and
thunderstorms through this afternoon.

OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY...

Monday: Early morning MVFR possible in cigs at KGON, otherwise
VFR.

Tuesday: MVFR or lower in chance of showers and thunderstorms.

Wednesday: VFR.

Wednesday Night - Thursday: MVFR or lower in chance of showers
and thunderstorms.

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

.MARINE...
Ahead of an approaching frontal system, southerly winds will
strengthen to around 15 kt on the ocean waters by morning,
increasing seas around 5 ft. A SCA has remains in effect today and
tonight between Fire Island Inlet and Montauk Point.

Sea up to 5 ft may linger on the ocean waters daytime Mon per NWPS
and GFSwave, especially out east. Confidence in this is low as
sustained winds in the persistent S flow daytime Sunday peak only
briefly between 15-20 kt, and will be lighter out of the SW daytime
Mon, so SCA has not been extended into this time frame.

.HYDROLOGY...
-- Changed Discussion --A Flood Watch is in effect for the entire CWA late tonight and
Sunday.u

There is the potential for a significant to major flood event today
as a frontal boundary works across the area. All of the area except
eastern LI is under a Moderate Risk for Excessive Rainfall. The
potential is there for scattered to numerous flash floods. On
average, we are looking a widespread 1 to 3 inch rainfall with
localized amounts 4 to 6 inches. At this time, its hard to rule out
the potential for a few isolated spots receiving 7+ inches.
Rainfall rates of 1 to 2 inches per hour remain likely.
Confidence continues to increase for someone in the CWA to see
localized significant flooding.

A marginal risk of excessive rainfall is forecast for the Hudson
Valley for Tuesday, as another passing disturbance helps generate
showers/tstms with heavy rainfall. An ongoing risk may continue with
successive systems later this week.-- End Changed Discussion --

.TIDES/COASTAL FLOODING...
There is a high risk of rip current development at all the ocean
beaches today and Monday as southerly swells increase.

.OKX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --CT...Flood Watch through this evening for CTZ005>012.
NY...Flood Watch through this evening for NYZ067>075-078>081-
176>179.
High Rip Current Risk until 9 PM EDT this evening for NYZ075-
080-081-178-179.
NJ...Flood Watch through this evening for NJZ002-004-006-103>108.
MARINE...Small Craft Advisory until 6 AM EDT Monday for ANZ350-353.-- End Changed Discussion --