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Forecast Discussion for New York City/Upton, NY

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077
FXUS61 KOKX 212016
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
416 PM EDT Sun Jun 21 2026

.WHAT HAS CHANGED...
While overall rainfall totals have decreased slightly, high
hourly rates are still possible Monday afternoon into Monday
night. There is still potential for isolated flash flooding.

Portions of northeast NJ and NYC are now in a slight risk (level
2/5) of severe thunderstorms for Monday afternoon and evening.

Small Craft Advisory issued for the ocean waters, the NY Harbor
and the South Shore Bays.

High Rip Current Risk issued for the ocean beaches of NYC,
Nassau and western Suffolk

&&

.KEY MESSAGES...
1) Isolated late day showers and a rumble of thunder possible,
mainly across the interior.

2) Heavy showers and thunderstorms Monday afternoon and night
will bring the potential of urban and poor drainage flood
impacts, as well as localized flash flooding. A severe
thunderstorm can also not be ruled out.

3) Showers and thunderstorms are possible again Thursday and
Friday.

4) A high rip current risk expected for late day Monday for the
ocean beaches of NYC, Nassau and western Suffolk, and may be
ongoing at all the ocean beaches into part of Tuesday morning.
See Marine section for details.

&&

.DISCUSSION...
.KEY MESSAGE 1...
The passage of a shortwave this afternoon along with some
surface convergence along sea breezes and a surface trough may
develop isolated shower activity. Instability is very shallow,
but there is decent agreement in a few hundred J/kg of CAPE
between -10 and -20 C to support a few lightning strikes (with
the exception of the HRRR which appears to be over mixing).
Dry sub-cloud layer also supports locally gusty winds in any of
the isolated showers. Any shower development this afternoon
will quickly dissipate this evening as the shortwave energy
passes to the east.

.KEY MESSAGE 2...
Low pressure over the Mississippi Valley will continue to move
east toward our area this evening. At the same time, an
associated warm front will approach from the south and linger
over or near the area before the low pulls a cold front through
early Tuesday morning. This system will pull up tropical
moisture from the south with guidance consistently showing PW
around 2 inches. This combination brings the threat for
potential heavy showers and thunderstorms Monday afternoon
through Monday night.

Latest guidance continues to struggle on placement of the warm
front as well as heaviest axis of precipitation. However, CAM`s
have started hinting at more widespread higher totals being
farther north across the Lower Hudson Valley and southern CT.
This can be seen in the 12Z HREF LPMM with a few stripes of
1.5-2.0 inches in these areas. Given this environment, any
shower or thunderstorm that does develop will have the potential
to put down high hourly rates, mainly up to 1.0-1.5 inch/hr, but
upwards to 2 inches in one hour can not be ruled out. This can
be seen in the 12Z Hi-res guidance on the WPC URRD with a few
members showing just under 2 inches in one hour. Confidence is
still too low at this time for the issuance of a Flood Watch.
While these higher rates do cause concern for urban areas, if
they occur elsewhere they will likely not cause flash flooding
due to how dry we have been. There is too much uncertainty in
coverage and location. Additionally, several area river and
streams are running well below normal, toward their 10th
percentile. This helps lower the risk for river and stream
flooding. Guidance will have to continue to be monitored over
the next 24 hours as a Flood Watch can not be completely ruled
out.

Additionally, while confidence is still relatively low, there is
potential for some of these thunderstorms to become severe. This
is mainly due to the potential location of the warm front and
decent low level curvature in model hodographs. The main threats
will be damaging wind gusts and an isolated tornado. The SPC has
nudged a slight risk of severe tstms into Staten Island and
Union County in NE NJ, and a 2% tornado risk into all of NE NJ
and NYC. Except for far eastern Long Island and SE CT, the rest
of the area is under a marginal svr risk.

.KEY MESSAGE 3...
Southwest flow aloft looks to set up by late Thursday into
Friday ahead of the next shortwave/cold front. This would help
to trigger the potential for showers and a few thunderstorms.
Confidence is starting to increase that the greatest potential
ends up on Friday when the shortwave axis is currently progged
to move across the area. Any severe/hydro impacts are uncertain
at this time since this is 5-6 days out.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Hi pres builds in tngt, followed by an approaching frontal sys
for Mon.

Mainly VFR thru tngt. Some showers with brief MVFR cond are
possible til about 00Z. Can`t rule out thunder as well, but
not high enough probability to include in TAF.

A few shwrs possible aft 14Z Mon with a warm front, then IFR
cigs expected after 18Z. Heavier shwrs and tstms possible late,
but mainly aft 00Z Tue, so held off including in the TAF except
for KSWF where probs are earlier.

NW-W winds this aftn weaken and give way to sea breeze flow.
Winds then become light/variable aft 00Z into Mon mrng. E-SE
flow around 10 kt develops aft 14Z.

Some mrgnl LLWS may develop close to 00Z Tue.

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

Some variability in wind direction can be expected thru
this eve.

Any shwrs or tstms this aftn will be capable of producing wind
gusts aoa 35 kt. Coverage and prob too low to include in TAF.

.OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY...

Rest of Monday: Becoming IFR with locally hvy shwrs and tstms
developing, especially aft 00Z. E winds becoming S.

Tuesday: IFR in the mrng, becoming VFR. N flow 10-20 kt.

Wednesday: VFR with NW flow.

Thursday: VFR with increasing S flow.

Friday: MVFR or lower possible in shwrs and tstms.

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

&&

.MARINE...
A southerly flow will strengthen as low pressure approaches from
the west. All waters except the Sound and Peconic/Gardiners Bays
are now under a Small Craft Advisory from late Monday through
Monday night. This is due to 25-30 kt gusts and 5-ft seas for
the ocean waters. There is potential for the other waters to
be added in subsequent forecasts.

Thereafter, winds and seas should remain below SCA criteria.

Rip Currents:

The rip current risk for the rest of today is moderate at the
Suffolk beaches, where a 3-ft S swell @ 7 seconds persists.

On Monday, the rip current risk will be moderate for much of the
day, then increase to high after 5 PM at the ocean beaches of
NYC, Nassau and western Suffolk as S flow increases to 20 kt and
associated wind waves build to 4-5 ft, at a time when lifeguards
and beach patrols will be coming off duty. RCMOS forecast
followed for the most part as it is well aligned with the trend
in winds/seas.

The high risk will expand to all ocean beaches Mon night, and
may still be ongoing into part of Tue morning especially at
the Suffolk beaches, as residual 3-4 ft wind waves continue
with winds still partly onshore. Otherwise, a mostly moderate
risk expected for Tue as winds turn offshore and seas slowly
subside.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...High Risk for Rip Currents from Monday afternoon through Monday
     evening for NYZ075-080-178-179.
NJ...None.
MARINE...Small Craft Advisory from 2 PM Monday to 6 AM EDT Tuesday for
     ANZ338-355.
     Small Craft Advisory from 6 PM Monday to 6 AM EDT Tuesday for
     ANZ345-350-353.

&&

$$

DISCUSSION...JT
AVIATION...JMC
MARINE...BG/JT

Previous Forecast Discussions may be found at
NWS New York City/Upton, NY (OKX) Office Forecast Discussions.
(Click 'Previous Version' there to view past versions successively.
Some may differ only in time posted.)

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