Groton, Connecticut 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

405
FXUS61 KOKX 200802 CCA
AFDOKX

Area Forecast Discussion...CORRECTED
National Weather Service New York NY
402 AM EDT Thu Aug 20 2026

.WHAT HAS CHANGED...
A Flood Watch has been issued for northeast NJ, NYC, Southern
Westchester and western Long Island.

Confidence in heavy rainfall resulting in flash flooding has
increased as well as total rainfall amounts.

The SPC has lifted the marginal risk of severe weather into
portions of our area including most of northeast NJ, NYC and
western Long Island.

&&

.KEY MESSAGES...
1) Showers and potential thunderstorms move through the area
this afternoon through the evening. A period of heavy rainfall
is possible, particularly for northeast NJ, NYC, southern
Westchester and Western Long Island, where a Flood Watch is now
in effect. For the Watch area, peak hourly rainfall rates could
reach around 2 inches with total rainfall amounts expected to be
between 1.5 and 2.5 inches with locally higher amounts
possible.

2) Unsettled weather is expected again this weekend.

&&

.DISCUSSION...
.KEY MESSAGE 1...
A cold front approaches the area today and will stall offshore
through the weekend while the eastern US remains under a
persistent upper level trough. A shortwave rounding the base of
this trough can currently be seen entering the Ohio Valley. This
shortwave will continue to approach our area and aid in
development of a frontal wave. An area of showers and potential
thunderstorms will move through the area this afternoon through
the evening and bring a potential period of heavy rainfall.

Guidance has come into better agreement over the past 24 hours that
this frontal wave will likely track just south of the area. Even
though we will likely fall just north of any significant
instability, strong dynamics are expected given a right entrance
region of an upper level jet, the aforementioned shortwave and
frontogenetic forcing. This forcing will be moving towards a plume
of high pwat (2+ inches) that looks to just stretch into our area.
Additionally, deep saturation is seen in model soundings with the
warm cloud layer approaching 15kft. Most CAMs are in agreement with
this set up being able to produce rainfall rates as high as around 2
inches in one hour. The CAMs have also come into a bit better
agreement that these rates could extend into southern portions of
our area. This is seen in the latest HREF which shows the northern
extent of the 30% chance of 3 inches in 3 hours just touching our
southwestern most zones. This has been an indicator of flash
flooding for events in the past.

Given all of this, confidence is high enough to issue a Flood Watch
for northeast NJ, NYC, southern Westchester and western Long
Island. The Watch runs from 2pm today through 2am Friday, but
may be able to come down a bit earlier for the zones west of
Long Island. Some of the latest guidance really slows the wave
as it passes south of Long Island. This could bring lingering
moderate to heavy rainfall for eastern locations through
tonight. At this time, this is not the likely scenario given
loss of more significant forcing, however, if guidance
continues to trend in this direction, an expansion of the Watch
farther east for Long Island and southern CT can not be
completely ruled out.

While still low confidence, given high shear and little
instability, severe thunderstorms for northeast NJ, NYC and
western Long Island can not be completely ruled out. This would
be mainly an isolated damaging wind gust threat, but given
decent low level curvature in model soundings an isolated
tornado is also possible.


.KEY MESSAGE 2...
Guidance continues to struggle with the next wave of low
pressure for the first half of the weekend as the upper level
trough become negatively tilted. Regardless, another period of
moderate to heavy rainfall is possible. The WPC continued to
include the entire area in a marginal risk of excessive
rainfall.

A cold front approaches on Sunday and will bring a chance of
afternoon/evening thunderstorms. CIPS and CSU MLP continue to
hint at the potential for severe thunderstorms, but it is still
too far out for any specifics.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
A cold front approaches the terminals later Thursday, with an
associated wave of low pressure forming along it. The front and low
pressure will move east of the region late Thursday night.

VFR conditions start out the TAF period until Thursday afternoon.
There could be some brief MVFR to IFR within showers and/or
thunderstorms especially within any heavier rainfall. Timeframe for
these is generally between 18Z and 02Z, relatively earlier farther
west and relatively later farther east. Showers could linger into
early AM Friday but overall, expecting mainly VFR conditions to
return late Thursday night.

Winds during the TAF period will be less than 10 kts but direction
will be quite variable. Low confidence with the wind direction
forecast. We will likely see some terminals have their sea
breezes latter half of the afternoon into early evening. Towards
end of TAF period, a general more northeast to north flow is
forecast.

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

Amendments possible to refine timing of showers/thunderstorms, which
could be a few hours off from TAF.

If confidence increases in thunderstorms, PROB30s will become
TEMPOs.

Amendments possible for the timing of IFR and MVFR, which could be a
few hours off from TAF.

.OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY...

Friday: Mainly VFR. A few showers and MVFR possible during the day.
Higher chances of showers and MVFR late at night.

Saturday: Showers likely. Possible thunderstorms. MVFR to IFR
at times.

Sunday: A chance of showers. Possible thunderstorms. Chance of MVFR
or lower at times.

Monday: VFR.

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

&&

.MARINE...
Sub-SCA conditions generally continue through the middle of next
week. However, with some uncertainty in strength of a wave of low
pressure tonight into Friday, brief 25kt gusts can not be ruled out.

Rip Currents: There is a low risk of rip currents today and Friday
given lack of significant winds and weak swell components. There is
potential for forecast winds to trend higher for tonight into
Friday, but this would be out of the E/NE which should not be enough
to increase the risk level.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...Flood Watch from 2 PM EDT this afternoon through late tonight
     for NYZ071>075-078-080-176>179.
NJ...Flood Watch from 2 PM EDT this afternoon through late tonight
     for NJZ002-004-006-103>108.
MARINE...None.

&&

$$

DISCUSSION...JT
AVIATION...JM
MARINE...JT