NWS New York, NY wrote its last area forecast discussion before the first event at Aug 12, 5:29 PM EST, 1 hour 6 minutes earlier.
Area forecast discussion, Aug 12, 5:29 PM EST, 1 hour 6 minutes before
Area Forecast Discussion
National Weather Service New York NY
629 PM EDT FRI AUG 12 2016
.SYNOPSIS...
The heat wave will continue through the weekend. A cold front
will slowly approach on Sunday, pass through Sunday night, and
stall to the south from Monday into Tuesday. The front will return
north as a warm front Tuesday night into Wednesday morning, with w
weak low pressure trough lingering from later Wednesday into
Thursday. A weak cold front will pass late Thursday night into
Friday.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
Scattered thunderstorms were developing at 19Z across the region.
There was still a little CIN across southeastern Connecticut and
eastern Long Island, but this should be overcome across most of
the area by 5 pm. LAPS has VGP around 0.25 across the area, so
there is an enhanced severe risk where boundaries can locally
increase the shear and lead to better organization. Wet
microbursts will remain a threat with the strongest storms.
Satellite shows a band of cirrus drifting through the area, so
this may be indicative of some upper level convergence and a
limiting factor for thunderstorm development through about 5 pm.
Heat indices were around 105 across almost all of the county
warning area. As a result, the excessive heat warning was expanded
to include all but the Twin Forks of Long Island and coastal New
London county. In these areas, a heat advisory remains in effect
through Saturday.
Thunderstorm coverage should decrease after 3Z, but continued
activity cannot be completely ruled out due to potential residual
boundaries.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
The airmass is virtually unchanged for Saturday, so forecast heat
indices should closely resemble Friday. A blend of various data
was used to populate the temperature and dewpoint grids, with the
MAV notably too cool but the GMOS close with regard to dewpoint.
Chances for scattered thunderstorms again, particularly in the
afternoon and evening. There is actually quite a bit of DCAPE
progged by the NAM, with over 1000 J/kg. In addition, there is low
level directional shear and high EHI. Main limiting factor is
still a lack of deep layer shear, with only about 20-25 kt progged
which is not adequate to balance the high CAPE. Regardless, if
storms do develop there will be a severe threat.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
***HEAT AND OPPRESSIVE HUMIDITY TO CONTINUE INTO SUNDAY***
Front approaching on Sunday looks slower to arrive. Given model fcst
H8-10 thicknesses similar to those of today and WSW flow, little
change in air mass otherwise, even some pre-frontal compressional
warming, see no reason not to continue to forecast temps 3 deg or so
above combined MET/MAV guidance, with highs in the mid/upper 90s,
and dewpoints siding closer to more humid MAV numbers, mostly mid
70s, with some afternoon mixing to the lower 70s confined mainly to
NYC metro. With this in mind, have high confidence in heat index
reaching or surpassing 100 over most of the area, possibly 105 for
NYC metro, Long Island, the Hudson Valley, and coastal and SE CT,
and those areas which have hit 105 today. Have therefore extended
the Excessive Heat Warning into Sunday for all but coastal New
London and eastern Long Island, and even there higher dewpoints may
put the heat index close to 105 with oppressively humid maritime air
coming in via onshore flow.
Approaching cold front should trigger sct thunderstorms mainly
inland late Sunday afternoon, then spreading toward the coast Sunday
evening. Mid level winds 35-40 kt, slow moving nature of the front,
mainly unidirectional flow parallel to the front, and PW over 2
inches suggest stronger storms capable of producing damaging winds
and very heavy rain.
Conditions should be less oppressive Mon-Tue after the weak fropa,
with somewhat lower temps (highs upper 80s/lower 90s) and humidity
levels (dewpoints around 70), with max heat indices still reaching
90-95. A warm front will then approach late Tuesday night into
Wednesday, with chances for thunderstorms, and timing of fropa
somewhat uncertain at least per model guidance. ECMWF is probably
too fast with warm fropa Tue night, and GFS may be too suppressed,
stalling the warm front over the area or just to the south all day
Wednesday due to its flatter ridging to the south and a slightly
stronger northern stream over the Canadian Maritimes. Climatology
and model biases argues for suppression Tuesday night, and then warm
fropa Wednesday morning.
Expect high temps mainly 85-90 Wed-Fri, with high humidity on Wed
and possibly Thu, then drier conditions Fri after a weak cold
frontal passage.
&&
.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
High pressure remains anchored off the Mid-Atlantic coast into
Saturday afternoon.
Primarily VFR through the TAF period. However, with threat of
isolated-scattered showers/thunderstorms into this evening cannot
could see brief period of MVFR or lower conditions if a stronger
storm passes over a terminal. If any storm were to pass over a
terminal, could also see gusts to at least 30-40 kt as well.
Scattered convection in the NY Airspace, and convection will
continue to develop into this evening. Will continue to carry TEMPO
groups indicating potential for SHRA/TSRA to impact the terminals
through around 02Z.
Lastly there is also a very low chance for MVFR fog and/or stratus
early Saturday morning, but confidence in this is too low to
reflect in the TAFs.
Generally SW flow 10 KT or less for most terminals, but S flow
10-15 KT at coastal terminals. SW flow continues into Saturday,
with afternoon sea breezes likely.
...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: SHRA/TSTMs possible through around 2z. Brief
period MVFR or lower and gusty winds possible if a storm goes
right over terminal.
KLGA TAF Comments: SHRA/TSTMs possible through around 2z. Brief
period MVFR or lower and gusty winds possible if a storm goes
right over terminal.
KEWR TAF Comments: SHRA/TSTMs possible through around 2z. Brief
period MVFR or lower and gusty winds possible if a storm goes
right over terminal.
KTEB TAF Comments: SHRA/TSTMs possible through around 2z. Brief
period MVFR or lower and gusty winds possible if a storm goes
right over terminal.
KHPN TAF Comments: SHRA/TSTMs possible through around 2z. Brief
period MVFR or lower and gusty winds possible if a storm goes
right over terminal.
KISP TAF Comments: SHRA/TSTMs possible through around 2z. Brief
period MVFR or lower and gusty winds possible if a storm goes
right over terminal.
.OUTLOOK FOR 18Z Saturday through Wednesday...
.Saturday afternoon-Wednesday...Mainly VFR. However, scattered
afternoon/evening SHRA/TSRA each day could result in brief MVFR or
lower conditions.
&&
.MARINE...
A small craft advisory remains in effect for tonight on the
ocean. Wavewatch has been running high so have adjusted seas
downward through Saturday night. Conditions could deteriorate to
small craft advisory levels again Saturday night. Elsewhere,
scattered thunderstorms capable of producing strong winds will be
the main threat.
There is an outside chance 5-ft seas could linger into Sunday
morning, otherwise expect winds (outside of thunderstorms) and
seas to stay below SCA criteria from Sunday through Wednesday night.
&&
.HYDROLOGY...
With precipitable water remaining generally between 2 and 2.5
inches, any thunderstorms that develop through Saturday will be
capable of producing torrential rainfall. With storm motion
generally expected to be less than 20 kt, there will be the threat
of localized flash flooding from any slower moving strong storm.
Thunderstorms with a cold frontal passage late day Sunday into
Sunday night, and with a warm frontal approach and passage late
Tuesday night into Wednesday, may be capable of producing torrential
rainfall with rainfall rates 1-2 inches per hour and localized flash
flooding.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 10 PM EDT Sunday for CTZ012.
Excessive Heat Warning until 10 PM EDT Sunday for CTZ005>011.
NY...Heat Advisory until 10 PM EDT Sunday for NYZ079-081.
Excessive Heat Warning until 10 PM EDT Sunday for NYZ067>075-
078-080-176>179.
High Rip Current Risk until 9 PM EDT this evening for NYZ075-
080-081-178-179.
NJ...Excessive Heat Warning until 10 PM EDT Sunday for NJZ002-004-
006-103>108.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ350-353-
355.
&&
SYNOPSIS...JMC/Goodman
NEAR TERM...JMC
SHORT TERM...JMC
LONG TERM...Goodman
AVIATION...Maloit/MPS
MARINE...JMC/Goodman
HYDROLOGY...JMC/Goodman