Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 231336
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
936 AM EDT Sun Apr 23 2017

.SYNOPSIS...
High pressure builds over the northeast today and moves offshore
of southern New England late today into Monday. A wave of low
pressure over the southeastern states moves off the southeast
coast Monday, then tracks up along the eastern seaboard through
midweek. High pressure will build back in for the end of the
week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Region will lie in a near zonal upper flow today between a
polar upper low over Hudsons Bay and a closing upper low moving
through the deep south. At the surface...high pressure builds
into the region this morning and then east this afternoon into
tonight.

Mostly sunny conditions today with sunshine occasionally filtered
by jet cirrus. Light NE flow in the morning expected to give
way to afternoon return flow and s/se sea breezes. Early/mid
afternoon sea breeze will limit temps along the south coastal
areas to the upper 50 to lower 60s...and mid 60s for NYC/NJ
metro with mid to late afternoon sea breezes. Temps across the
far N & W interior should be able to rise into the upper 60s to
around 70 with deeper mixing and outside of maritime influence.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
The surface high moves offshore of the southern New England
coast tonight into Monday as the weak zonal flow remains
aloft. Meanwhile in the southern stream a low closes off over
the Tennessee Valley this morning and then moves slowly in the
flow. The low emerges from the southeastern coast late tonight
into Monday. The northward progression of the low will depend on
the strength of the surface high nosing into the coastal plain.
With the weakening of the high late Monday the low will then
start to move northward. As a result much of the area will
remain dry through Monday with slight chances mainly late Monday
morning into the afternoon across NYC and Long Island.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Monday night into Tuesday the NAM becomes slower than other
guidance in moving the low north, and leaned toward the slightly
faster solutions as the northern high continues to weaken and
little ridging remains aloft. The system will remain rather weak
and then weaken Tuesday night into Wednesday and the upper low
moves along a northern stream trough digging into the central
states as a mid Atlantic ridge builds.

Timing and amplitude differences become more apparent in the H5
pattern at the end of the week and into next weekend.

Winds will increase and become gusty Mon night and Tue. 30-40
kt LLJ lifts through Tue aftn/eve...but a low level inversion
should keep most of these winds aloft. These stronger winds will
also depend on where the low tracks. If the low tracks over NYC
the higher winds will remain to the east.

The forward progression of the system is also uncertain...and
current forecast may be too quick decreasing pops to chc Wed
morning. System departs Wed night with ridging aloft developing
over the east and a broad trough out west. This will lead to
warming temps through the remainder of the week. A cold front
moves towards the area on Thu...but most guidance has
showers/tstms mostly dissipating before it reaches the region.
This front is then forecast to stall near the area into next
weekend with potential waves of low pressure keeping it
unsettled.

As for temperatures, near seasonable levels through mid week,
if not a bit cooler during the daytime due to cloud cover and
rain. A significant warmup is possible for the end of the week
with rising heights aloft.

&&

.AVIATION /13Z SUNDAY THROUGH THURSDAY/...
VFR as high pressure builds from the west this morning and passes
east this afternoon.

N-NNE winds this morning will turn to the S-SE early this
afternoon. Timing of wind shift may be off by 1-2 hours in
TAFs. Speeds will be 10 kt or less.

Winds diminish tonight and become light and variable outside of
city terminals.

.OUTLOOK FOR 12z MONDAY THROUGH THURSDAY...
.Monday...VFR during the day. Chance MVFR in rain at night.
.Tuesday...IFR/LIFR in rain. NE gusts 20-25 KT near coast possible
during the day.
.Wednesday...MVFR possible early, becoming VFR.
.Thursday...VFR.

&&

.MARINE...
A long period east to southeast swell will slowly subside
through the day. Otherwise with high pressure building over the
forecast waters today winds and seas will remain below small
craft levels. The high will move offshore tonight into Monday. A
low pressure system will move off the southeastern coast
Monday, then track slowly northward along the coast into
Wednesday, and then weaken.

With an increased surface pressure gradient expected Monday
night into Tuesday night, easterly winds will increase, and
become gusty. Small craft gusts will become likely late Monday
night into Tuesday night across the forecast waters, with ocean
seas building to 5 feet or greater late Monday night into
Tuesday night. There will be the potential for gusts to approach
gale force on the ocean waters late Monday night into Tuesday
and possibly into Tuesday night. However, confidence is low as
mixing will be limited over the still cool ocean waters. Will
continue to highlight the potential in the HWO, Hazardous
Weather Outlook. A small craft advisory will likely be needed
for Monday night.

Ocean seas will be slow to subside and may remain at small craft
levels into Friday.

&&

.HYDROLOGY...
Between 1/2 and 1 1/2 inches of rainfall is possible late
Monday into Wednesday. Amounts will depend on the track of low
pressure moving along the eastern seaboard.

No hydrologic impacts are anticipated at this time.

&&

.TIDES/COASTAL FLOODING...
Potential for minor coastal flooding for vulnerable coastal
communities...mainly along the southern bays of Western LI and
Western LI Sound...with the Tue eve high tide cycle. This is in
response to a low pressure system moving northward along the
eastern seaboard. Only 1/2 to 1 ft of surge is needed to reach
minor flood thresholds Tue evening.

&&

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

&&

$$
SYNOPSIS...MET
NEAR TERM...NV
SHORT TERM...MET
LONG TERM...24/MET
AVIATION...DS
MARINE...24/MET
HYDROLOGY...NV
TIDES/COASTAL FLOODING...NV


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