Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
733 PM EDT sun Aug 30 2015
a surface trough will move into the region tonight and move south
of Long Island Monday. A back door cold front moves across late
Monday night. High pressure will keep hot and humid conditions
across the region through much of the week. A weak cold front will
move through Thursday night...but it will still be warm and mainly
dry through next weekend.
Near term /until 6 am Monday morning/...
forecast is generally on track. Adjusted probability of precipitation a bit this evening and
also made minor adjustments to T/TD/wind and sky grids to better
reflect current conds and trends.
Middle level shortwave and associated higher positive vorticity advection move mostly south
of the region with a stronger one tracking across southeast
Canada. At the surface...there will be a weak surface trough
moving towards the region. This will keep an abundance of clouds
overhead for the night. The lows were taken from the relatively
warmer side of guidance of the mav MOS...with values expected to
be warmer than the previous night with southwest flow.
Cooling temperatures with coverage of any convection remaining
decreasing into this evening. However...the environment will
still be somewhat unstable with some elevated instability ahead of
the surface trough. With these aforementioned factors...there will
be a slight chance for showers and thunderstorms for tonight
across all locations.
There is a continued moderate risk for the development of rip
currents into this evening.
Short term /6 am Monday morning through Monday night/...
the shortwave weakens south of the region Monday. A high amplitude
ridge from the west will begin to build in. However...at the
surface...the trough will remain and the daytime should enhance it
with the sea breeze giving some increase in the temperature gradient
within the region across the coast. The cooler temperatures will be
advected into the region from the more southerly flow. This will
converge against places that have southwest flow. The probability of precipitation overall
will not be high...just a slight chance of showers and thunderstorms
close to the coast...but with the airmass becoming increasingly warm
and humid...instability will be larger as cape increases to
approximately 500-1000 j/kg. Inland...drier conditions should
prevail. An overall very warm day expected. A mav/met blend was used
for highs...yielding values from the middle 80s to lower 90s across a
majority of the region.
Once the heating wanes down for Monday evening...the environment
will become more stable and the high amplitude ridge from the west
will continue to build in. The surface trough will have pushed south
of Long Island. There will be a weak back door cold front moving
across late. Overall...the greater influence will be from the
ridge and the subsidence from the ridging will lead to lessening
clouds. However...despite light winds...lows will not change too
much compared to the previous night. The relatively warm and
humid airmass will remain though as warm air advection increases
at the 850mb level.
There is a moderate risk for the development of rip currents on
Long term /Tuesday through Sunday/...
the main theme of the long term period will be the continuation of
heat and humidity across the region.
Models are in pretty good agreement with the 500 mb pattern across noam
through the period. A late season heat wave is expected for parts of
the tri-state area this week as a deep layered ridge encompasses the
eastern US. A southerly flow for much of the week will keep humidity
levels high as well. The hottest day...heat and humidity combined
looks to be Thursday with moisture pooling ahead of a weak cold
front. Not expecting heat advsy criteria to be met...although heat
indices will range between the upper 80s to lower 90s each afternoon
through Wednesday with 90 to 95 on Thursday. Although parts of NYC may reach a
95 degree heat index Thursday...not expecting it for 2 consecutive
days. Therefore...no advsy is anticipated for the city either.
It will be a fairly dry week with only a few showers/thunderstorms with the
weak boundary Thursday/Thursday evening and again Friday/Friday evening as another weak
boundary approaches from the north...this time with weak shortwave
energy. The flow becomes Ely Friday...but the combination of the upper
energy...low level convergence and the orographic influence could
trigger a few showers/tstms.
The onshore flow will also provide some relief from the heat
especially at the coast Friday through sun. Temperatures will still be 5 to 10
degrees above normal though.
Aviation /00z Monday through Friday/...
a weak trough of low pressure will cross the tri-state this
evening...then stall out south of Long Island into Monday.
VFR conditions are anticipated through the taf period. An isolated
shower or thunderstorm cannot be ruled out...but confidence very low
for any activity to impact any particular Airport.
Winds become SW under 10 knots at city terminals tonight and light SW
or variable elsewhere. West-southwest-west-northwest winds at around 10 knots develop by middle
to late Monday morning and into early Monday afternoon. Wind speeds
should increase during the afternoon...10 to 15 knots. Occasional gusts
to 20 kts possible...especially at kjfk.
Outlook for 00z Tuesday through Friday...
Monday night-Wednesday night...VFR. Afternoon seabreezes probable
Thursday...most likely VFR. Isolated showers/thunderstorms
possible. Afternoon seabreezes probable.
Friday...most likely VFR. East winds g15-20kt possible. Isolated-
scattered showers/thunderstorms possible.
primarily a weak pressure gradient through Monday night. The winds
will be mainly less than 15 knots out of the southwest to south.
There could be a round of gusts Monday afternoon but these are
expected to be up to 20 knots. Seas on the ocean may get to 5 feet
Monday night. However...with the weak pressure gradient...did not
think winds would supply a strong enough fetch to increase seas to
5 feet. Therefore capped the ocean seas at 4 feet Monday night.
Sub-advsy conds are expected on all waters through the
remainder of the period.
any shower or thunderstorm through Monday could result in a brief
heavy downpour...with perhaps a quick quarter of an inch in
rainfall amounts. There could be some locally minor flooding but
confidence in this is low with coverage of convection forecast
Overall...no widespread significant rainfall is forecast through
with a recent full moon...brief minor inundation is possible
during the times of high tide across the typically vulnerable
coastal locales into the start of the work week.