Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 140620
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
220 AM EDT Tue Aug 14 2018

.SYNOPSIS...
A slow moving low will be in the vicinity through Tuesday, then
finally exit eastward Tuesday night. Weak high pressure will slide
across Wednesday into Thursday night. Low pressure and an attendant
frontal system will approach on Friday, then move across Friday
night. Weak high pressure then builds in on Saturday and Saturday
night. Another weak low will cross the area on Sunday, followed by
weak high pressure briefly returning on Monday.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Upper low to our west opens and shifts NE towards central NY. At
the surface, a stationary front runs across the tri-state area.
Not much on radar as of midnight, but isolated showers and
thunderstorms could pop up at any time. Have lowered PoPs and
adjusted cloud cover forecast based on latest observations and
trends. May need to add some fog to the forecast across Long
Island where cloud cover had diminished earlier this evening.
Satellite indicates some stratus trying to spread there, which
could prevent dense fog from forming. Low temperatures will be
averaging around 70.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
Showers and isolated thunderstorms are expected to redevelop as
the mid-upper level low shifts eastward increasing cyclonic flow
and lift over the area on Tuesday. This will help convective
initiation, resulting in more showers and possible thunderstorms
especially during the late morning-afternoon hours.
Southwesterly flow will develop increasing low level moisture
and keeping the threat of flash flooding over areas that
received heavy precip today and over this past weekend.

As the associated surface trough passes to the east Tuesday
night, drier air will filter in, bringing an end to the
rain/storms sometime Wednesday morning.

There is a moderate risk of rip currents for Atlantic beaches
through Tuesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
At the start of the period, the upper low responsible for heavy
rain and flash flooding of late will open up into a trough and
lift out on Wed. While a weak sfc trough may persist, an upper
ridge will be moving across from Wed into Thu night and keep the
area mostly dry, with only slight chance PoP sneaking into
western sections Thu night as heights aloft begin to fall with
passage of the ridge axis.

With more in the way of sunshine late this week, a 3-day period
of 90-degree heat looks likely for the NYC metro area from Wed
into Fri. Dew points on Wed look like they should be low enough
to keep the heat index from touching 95, but as dewpoints
increase ahead of the next frontal system, heat index values
should exceed 95 on Thu and possibly Fri in NYC and surrounding
areas, possibly also up the Hudson River Valley and into SW CT.
Heat advisories will probably be needed for Thu-Fri, with just a
little lingering uncertainty for Fri, as max temps and heat
index values could fall short if convective initiation with an
approaching weak low and trailing frontal system were to begin
earlier than the expected late day time frame. More about this
frontal system in the Hydrology section.

Sat should be more on the dry side, with only slight chance PoP
as the area sits in between the departing frontal system and a
sharpening upper trough to the west while a weak sfc trough and
marginal instability linger. This trough is forecast to close
off into an upper low as it moves into New England on Sunday,
with another chance for showers. Monday looks dry with weak
ridging sfc and aloft moving across.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Low pressure and an attendant stationary front will lift north
this morning. An upper level low will approach this afternoon.

IFR cigs possible at the NYC metros and KISP late tonight til
around sunrise just before the front jumps northward and
southerly flow commences. Gradual improvement through MVFR and
then VFR expected after sunrise and into early afternoon, with
S-SW flow around 10 kt, and some G15-18KT at the NYC metros and
KISP. As the upper low approaches, chances for tstms with IFR
conds and gusty/erratic winds should increase after 18Z-20Z from
the NYC metros north/west. Some of this activity could make it
to KBDR/KISP toward evening.

.OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY...
.Tonight...MVFR conds possible in leftover showers and isold
tstms, manly in the evening.
.Wednesday-Thursday...Mainly VFR.
.Friday...MVFR or lower conds possible in late day/evening
showers/tstms from the NYC metros north/west.
.Saturday...Mainly VFR.

&&

.MARINE...
Made minor changes with this update to reflect the latest
trends in observations and guidance. The forecast appears on
track.

Winds and seas will remain below SCA levels through Tuesday,
although any tstms that develop could produce locally hazardous
conditions. A brief period of increasing southwesterly flow
Tuesday night into early Wednesday could produce waves around 5
ft on the ocean waters. During the late week period, winds
should remain rather light, and seas should remain below 5 ft on
the ocean waters, and 1 ft or less on non ocean waters.

&&

.HYDROLOGY...
Rainfall amounts through Tuesday night should average below a
half inch, however locally up to an inch or two of rain is
possible in thunderstorms. Any area that does experience
locally heavy rainfall, given very wet antecedent
conditions,could experience localized flash flooding.

There should be a lull in the precipitation from Wednesday
through Thursday.

An approaching frontal system could produce showers/tstms with heavy
rain Fri afternoon and evening. Given PW increasing to over 2 inches
and deep later SW flow nearly parallel to the approaching frontal
boundary, there is potential for heavy rain with individual cells
and also training of cells, mainly from the NYC metro area
north/west.

&&

.TIDES/COASTAL FLOODING...
While overall tidal levels continue to slowly fall, there is
still some potential for high tides to be around minor coastal
flood benchmarks Tuesday night over the south shore back bays of
New York City and Nassau County. A coastal flood statement may
be needed for this.

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off
the air for an extended period of time.

&&

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

&&

$$
SYNOPSIS...Maloit/99
NEAR TERM...JC/Maloit/99
SHORT TERM...99
LONG TERM...Goodman
AVIATION...JMC/Goodman
MARINE...Goodman/Maloit/99
HYDROLOGY...Goodman/Maloit/99
TIDES/COASTAL FLOODING...
EQUIPMENT...



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