Flash Flood in Connecticut, September 19, 2016

Area Forecast Discussion
National Weather Service New York NY
756 AM EDT MON SEP 19 2016

.SYNOPSIS...
A weakening frontal system will move into the area today and
tonight, then slowly pass just to the south on Tuesday. High
pressure from the Ohio Valley will then build in through mid week,
before slowly shifting offshore Thursday and Thursday night.
Another cold front will approach from the north Friday night, and
move across early Saturday. Canadian high pressure will then
settle in for the remainder of the weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Radar shows two areas of concern for heavy rainfall: One band
that has developed along the leading edge a cold pool laid down
by earlier showers/tstms, currently extending from Bridgeport to
NYC to Philadelphia that has produced local totals from 1.0-1.5
inches; and expansing area of heavy showers extending from the
ocean waters up across central and eastern Long Island. Given
motion of upstream activity in SE PA and southern NJ will have to
watch NYC metro, Long Island, and coastal and SE CT for potential
training of cells and at least minor if not localized flash
flooding. Still on target for many areas receiving over an inch,
with localized totals of 2+ inches. This rainfall courtesy of a
weakening front moving into the area, with favorable combination
of PW increasing to near 2 inches, upper level divergence in the
right rear quadrant of jet streak to the north, weak mid level
shortwaves moving up the coast, weak low level convergence on the
nose of a 25-kt southerly SW LLJ, and weak instability.

It will be warm and rather humid today, with high temps in the
upper 70s to around 80, and dewpoints in the upper 60s and lower
70s.

There is a moderate risk for rip currents at the ocean beaches.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Chances for showers/isolated thunder diminish tonight from west to
east, but cannot rule out periods of heavier showers out east via
any waves of low pressure riding along the weakening boundary.
Lows tonight will be in the 60s to lower 70s.

Still could see isold-sct showers on Tuesday especially in the
morning, especially closer to the coast, until the front passes a
little farther south and washes out. With more sunshine especially
north/west, except temps to rise to the lower and mid 80s in most
places, and upper 70s across far eastern Long Island and SE CT.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Jet stream stays north of the region Tuesday night through Friday
with a quasi-zonal flow in the mid to upper levels. By the weekend,
mid and upper level shortwave with associated jet stream push
southward into the Northeast.

At the surface, winds will shift to a more northwest direction as
high pressure builds in from the Ohio Valley Tuesday night. The high
pressure area centers over the region on Wednesday with sea breeze
development allowing for more onshore flow. The high then shifts
slowly offshore Thursday through Thursday night with a more
consistent return southerly flow developing. An ambient weak
pressure gradient will be in place Friday with a weakening cold
front approaching Friday night. The front moves across early
Saturday with Canadian high pressure to follow to close out the
weekend.

The next chances of rain showers will be mainly associated with the
cold front Friday night into Saturday but the previous run of the
ECMWF model indicated a weak area of low pressure near the region
which could present another chance of rain sometime Friday. However,
the more recent run has backed off of this scenario, keeping the
weak low and associated rain well south of the region.

Otherwise, expecting mainly dry weather with above normal
temperatures with the region being on the eastern side of a longwave
ridge extending from the Central through Eastern U.S. for much of
the long term. Behind the cold front for next weekend, the airmass
will be a much cooler one with temperatures forecast to be closer to
respective normal values. The gusty northwest flow will allow for
more efficient dry and cold air advection.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
A weak cold front slowly weakens over the area today. High
pressure gradually builds in tonight into Tuesday.

MVFR/IFR conds early this morning with stratus and moderate to
heavy rain shower activity. Band of +shra with embedded tsra is
sinking south of the nyc metro terminals this morning...and should
sink se of the eastern terminals through around 15z. This should
end the threat of tsra...but moderate to locally heavy rain will
continue in its wake. Rain should become more iso- sct through
the afternoon. Widely scattered shower activity could linger into
this evening...particularly for eastern terminals.

Uncertainty in degree of improvement of cigs this afternoon.
Likelihood for coastal terminals to remain mvfr/ifr through the
day...but potential for a period of improvement to vfr in the
afternoon for KEWR/KTEB/KSWF. With light winds and abundant
moisture...likelihood for mvfr/ifr conditions re-developing this
evening and continuing overnight...possible lifr or lower for
outlying terminals.

Generally light southerly flow today for coastal terminals...light
and variable interior. Light and variable winds tonight.

     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: Sparse tsra coverage through around 13z.
Ceilings likely remain at mvfr...possibly ifr...levels through the
day.

KLGA TAF Comments: Sparse tsra coverage through around 13z.
Ceilings likely remain at mvfr...possibly ifr...levels through
the day.

KEWR TAF Comments: Sparse tsra coverage through around 13z.
Brief vfr conds possible in the afternoon.

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

KTEB TAF Comments: Sparse tsra coverage through around 13z.
Brief vfr conds possible in the afternoon.

KHPN TAF Comments: Ceilings likely remain at mvfr/ifr levels
through the day.

KISP TAF Comments: Sparse tsra coverage through around 14z.
Ceilings likely remain at ifr levels through the day.

.Outlook for 12Z Tuesday through Friday...
.Tuesday monring...Improvement to VFR Tuesday morning.
.Tuesday Afternoon-Friday...VFR.
.Friday Night-Sat...MVFR or lower possible in any shra.

&&

.MARINE...
Winds and seas will remain below SCA levels through much of the
period. The next chance of SCA conditions could come Saturday
night and Sunday on the ocean, as a significantly cooler air mass
builds in on a gusty NW flow.

&&

.HYDROLOGY...
There is a threat for localized flash flooding today, with
potential for swaths of 2+ inches not out of the question,
especially across coastal/SE CT and Long Island. Otherwise,
rainfall of at least 1-1.5 inches of rain appears likely, with
minor urban and poor drainage flooding.

If heavy rainfall rates coincide with times of high tide today,
the urban flood threat would be exacerbated for low lying locales.

&&

.TIDES/COASTAL FLOODING...
Astronomical tide levels continue to run high. Water levels of
less than a foot above astronomical high tides today would reach
minor coastal flooding benchmarks. Some locations along Jamaica
Bay and the south shore back bays of Nassau County may come
close, especially if heavy rain occurs just before or coincides
with high tide.

&&

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

&&

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