Area Forecast Discussion
Issued by NWS Upton, NY

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FXUS61 KOKX 270245
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
1045 PM EDT Mon Sep 26 2016

.SYNOPSIS...
High pressure moves farther out into the Atlantic as a frontal
system approaches from the west tonight. This moves across
Tuesday morning but its associated cold front will become
stationary and linger not too far off the coast for the rest of
Tuesday through Wednesday. Then low pressure over the Ohio Valley
and Mid Atlantic states will move slowly up the coast from late
Wednesday night through Saturday night, bringing an extended
period of unsettled weather. The low will gradually move clear of
the area early next week.

&&

.NEAR TERM /THROUGH TUESDAY/...
The forecast is on track with no major changes made.

The upper level ridge moves east of the region out into the
Atlantic, making the way for an approaching large upper level
cutoff low tonight. The associated upper level jet moves into the
region tonight, with the right rear quad of enhanced lift moving
in by Tuesday Morning.

Expect increasing chances for rain overnight into daybreak
Tuesday along with increasing winds with developing low level jet.
A few gusts up to 30 mph could very well occur especially with
mixing down of momentum via the rain.

Used warmer blend of NAM12/GMOS tonight with abundant clouds,
increasing south to southwest winds and incoming rain to keep
less differences spatially between lows.

There is a moderate risk of rip current development at the ocean
beaches for Tuesday.

&&

.SHORT TERM /TUESDAY NIGHT/...
The upper level low remains nearly stationary Tuesday and Tuesday
Night. The associated jet remains across the Northeast with the
local region staying in the right rear quadrant where lift will be
enhanced.

At the surface, the cold front will move across from west to east
Tuesday morning. However, it appears to slow down on its trek
through the region, lingering out east during the day and then
slowly moving offshore. The front will be weakening at the same
time. The front looks to remain stationary offshore from the model
guidance and with approaching weak low along it, may bring a return
of rain showers for Tuesday night.

Rain showers continue across the region early and then will be slow
to diminish across the coast. Favorable setup for synoptic lift is
evident within the models so do not totally trust model QPF fields
verbatim. A chance of rain showers will remain along the coastline
going into the afternoon and the evening.

Went with middle of guidance using a combination of GMOS and ECS for
max temperatures Tuesday. For min temperatures Tuesday night, used a
combination of MET and ECS.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
There is high confidence in the large scale idea of a cutoff low
digging south from the Great Lakes and upper Ohio Valley Wed
morning, meandering about the Central Appalachians and Ohio Valley
from Thu into Sat night, then slowly weakening and lifting out
toward the Great Lakes and interior Northeast Sunday into Monday.
This should lead to an extended period of unsettled weather and
more much needed rainfall, but details on the timing of any
heavier rain are sketchy. GFS may be took quick to kick an
offshore frontal wave out to the NE and weak offshore ridging,
which would allow heavier rain to arrive late Wed night into Thu.
The idea of a slower offshore low helping to reinforce surface
ridging/cool air damming on its rear flank over New England and
into our area should lead to diminishing PoP or even a dry but
cloudy interval Wed afternoon and much of Wed night, with heavier
rain off to the west. This setup should also lead to a gusty ENE
flow from Wed night into Thu evening. Then as onshore low level
flow increases and flow aloft becomes more difluent, one favorable
time frame for heavier rain to take place may be Thu night.
Another may come Fri night into Sat morning as a mid level
shortwave and upper jet streak lift northward along the coast.

After these features pass, still expect unsettled wx to continue
into Sat night and possibly Sunday, and do not have a completely
dry forecast in terms of PoP until Monday as the upper low
finally weakens and lifts NE to the Great Lakes and interior
Northeast.

Temps should be near to slightly below average in this
unsettled regime.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Cold front approaches tonight and passes through the terminals in
the morning.

S winds will gradually veer through the night, becoming W behind
the cold front in the morning. Strongest winds will be near the
coast overnight due to better mixing with gusts around 20 kt,
possibly as high as 25 kt. Flow veers around to the S/SW in the
afternoon as front stalls offshore and area of low pressure
remains nearly stationary over the Great Lakes.

VFR through the first half of the night, then SHRA move in from
the west with the cold front lowering conditions to MVFR/IFR until
mid to late morning. Ceilings should gradually improve to VFR from
west to east 14Z to 17Z.

.Outlook for 00Z Wednesday through Saturday...
.TUE NIGHT through WED...VFR.
.THU through SAT...Potential IFR/MVFR in showers RA. NE winds
15-20 kt with gusts 25-30 kt possible.

&&

.MARINE...
Expecting winds to increase tonight ahead of the frontal system. SCA
conditions are expected for all waters after 00Z, lasting until 12Z
Tuesday. Then, SCA conditions will be more probable across the
ocean. The ocean seas are also expected to build to 5-6 ft late
tonight into early Tuesday, but SWAN guidance has been recently
overestimating by a foot with ocean seas, so have reduced seas
accordingly.

SCA conditions should REdevelop on the eastern waters on Wed,
then spread westward to all waters Wed night into Thu night via
an increasing pressure gradient between high pressure to the north
and broad/weak low pressure to the southwest, with ENE flow
gusting to 25-30 kt. GFS is alone in advertising a period of
possible gales and think this is overdone, but will keep mention
of low potential in HWO for sake of continuity. Hazardous ocean
seas should linger Fri into Fri night.

&&

.HYDROLOGY...
Between 1/4 to 3/4 inch of rain expected from midnight into
Tuesday morning. No hydrologic impacts are expected at this time
other than typical urban ponding.

Periods of heavier rain with a slow moving low pressure system
pose urban flood issues later this week, with the potential for a
couple of inches of rain.

&&

.TIDES/COASTAL FLOODING...
A persistent moderate easterly flow during mid to late week may
combine with increasing astronomical high tides associated with
the new moon on Friday to cause minor to locally moderate coastal
flooding late this week.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 8 AM EDT Tuesday for ANZ330-335-338-
     340-345.
     Small Craft Advisory until 8 PM EDT Tuesday for ANZ353.
     Small Craft Advisory until noon EDT Tuesday for ANZ355.
     Small Craft Advisory until 10 PM EDT Tuesday for ANZ350.

&&

$$

SYNOPSIS...Goodman/JM
NEAR TERM...JMC/JM
SHORT TERM...JM
LONG TERM...Goodman
AVIATION...DW
MARINE...Goodman/JM
HYDROLOGY...Goodman/JM
TIDES/COASTAL FLOODING...Goodman


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