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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KOKX 181540
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1140 AM EDT Fri Aug 18 2017

.SYNOPSIS...
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A cold front will slowly move east across the area late tonight, but
will linger across the eastern end of Long Island and Southeast
Connecticut. The front will not totally clear the region until
Saturday night. High pressure will then build in through the
beginning of next week, followed by a midweek cold frontal passage.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Heavy showers with embedded thunderstorms will move east across
Eastern Long Island and SE CT through 1 pm. Hourly rates in
excess of 1.5 inches per hour have caused flash flooding in
parts of Suffolk County and widespread minor to locally moderate
flooding from the NJ/NYC Metro area east this morning.

Satellite imagery shows a SW/NE dry slot advecting NE from VA/MD
across SE PA, that should advect NE across the Lower Hudson
Valley by 18z.

This will increase sfc based and low lvl instability resulting
in the development of convection mainly aft 20z this afternoon
from SW to NE.

The highest chc for severe wx will be from NYC N and W, where
SPC placed this area under a Slight Risk. The greatest threat
is for damaging wind gusts. Stay tuned.

Because precipitable water values remain high -- close to 2 to 2.2
inches, heavy rain causing mainly urban flooding will remain
possible.

There is a moderate risk of rip currents at ocean beaches,
potentially becoming high this afternoon.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
Models at times can struggle with the precipitation forecast
with the departure of large mid level ridges above 580dm. So,
forecast will adjust for this in situation where there is more
forcing and precip is too low and vice versa.

The upper level trough will be approaching the region tonight.
The height falls become more remarkable late tonight into
Saturday morning and this is when the trough moves eastward a
greater distance. The region will be getting closer to the right
entrance region of this jet. The trough amplifies and shortens
its wavelength during the day Saturday. 500mb heights lower
20-30 m from early morning until early evening. Vorticity still
increasing with height tonight and Sat looking at 925, 850, and
700mb levels.

Still have a threat of gusty winds and heavy rain with
thunderstorms tonight. High precipitable waters near 2 inches
still will be in place as will the vertical wind shear.

A cold front will continue to approach tonight. The cold front
moves into the region late tonight into Saturday but does not
totally clear the region until Saturday night.

However with aforementioned dynamics, pops still in place for
parts of the CWA during Sat evening with possibility for
isolated shower activity.

West to Northwest flow behind the cold front later Saturday
night and continued ridging will promote mainly dry conditions.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Shortwave trough pivots northeast of the region on Sunday, with
generally zonal upper flow over the region for early to mid of next
week, between southern ridging and a closed low moving into Hudson
Bay.

At the surface, high pressure builds into the region Sunday, and
then gradually sinks south and east of the region Monday into
Tuesday. The result will be dry and seasonably warm conditions on
Sunday, giving way to increasing heat and humidity Mon into Tue.
Perhaps some afternoon shower/tstm activity along a lee trough Tue
afternoon depending on any energy sliding through the upper flow
aloft, but low predictability at this point.

Decent model agreement with shortwave energy digging into the Great
lakes Tue into Tue Night and then towards the NE US on Wed. An
associated frontal system will bring the next chance for organized
shower and tstm activity late Tue into Wed.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
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A cold front approaches late today.

Showers and thunderstorms have worked their way out of the city
and are across the eastern half of the terminals late this
morning. However, MVFR/IFR ceilings continue in the wake. Some
improvement is likely this afternoon before another round of
showers and thunderstorms arrives around 21z. Thunderstorms are
likely this evening with the cold front approaching until about
01z. Gusty winds and heavy rain possible in any thunderstorm.

Southerly winds will increase this afternoon, mainly between 10
to 15 kts. Gusts to 25 kt possible across much of the region
this afternoon, but especially along the coast. Higher gusts
possible with any thunderstorm.

For tonight, fog/stratus with MVFR or lower conds may linger
through the overnight.

     NY Metro Enhanced Aviation Weather Support...

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

KJFK TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
this afternoon and evening.

The afternoon KJFK haze potential forecast is YELLOW...which implies
slant range visibility 4-6SM outside of cloud.

KLGA TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
afternoon and evening.

The afternoon KLGA haze potential forecast is YELLOW...which implies
slant range visibility 4-6SM outside of cloud.

KEWR TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
afternoon and evening.

The afternoon KEWR haze potential forecast is GREEN...which implies
slant range visibility 7SM or greater outside of cloud.

KTEB TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
afternoon and evening.

KHPN TAF Comments: MVFR cigs could prevail. Amendments possible
for timing and coverage of showers and thunderstorms this
afternoon and evening.

.OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
.Saturday-Monday...VFR. light NW wind becoming SW by Late
Sunday and Monday.
.Tuesday...Iso shra/tstms possible with MVFR or lower
conds...otherwise VFR.
-- End Changed Discussion --

&&

.MARINE...
SCA on ocean today through tonight with sub SCA on other waters.
Overall sub SCA conditions expected Sat and Sat night with
offshore flow developing behind cold front.

Winds and seas are expected to remain blw sca lvls on all waters
Sun thru Wed as high pressure builds across the waters.

&&

.HYDROLOGY...
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Heavy showers and thunderstorms resulted in 1 to 3 inches of rain
this morning from the Metro NJ/NYC area east across Long Island.

Another round of heavy showers and thunderstorms will be possible
this evening ahead of the cold front. Rainfall accumulations
are expected to be around a half an inch to an inch, with
locally higher amounts possible in thunderstorms.

It still remains difficult to pinpoint where heavier showers
and thunderstorms will develop. There is a chance of flash
flooding with the more likely flooding hazard being minor
flooding of poor drainage and urban areas especially tonight
with places that received heavy rain during the morning.

Impacts from potential showers and thunderstorms Tuesday into
Wednesday are uncertain at this point.
-- End Changed Discussion --

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ350-353-
     355.

&&

$$
SYNOPSIS...JM/NV
NEAR TERM...GC/JM
SHORT TERM...JM
LONG TERM...NV
AVIATION...IRD
MARINE...GC/JM/NV
HYDROLOGY...GC/JM/NV