Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
320 PM EDT sun Oct 4 2015
as Hurricane Joaquin moves out to sea well to our east through
Tuesday...high pressure will build into our region from the west.
The high will crest overhead on Thursday before moving off to our
east Thursday night. Low pressure may cross over or just north of
the tri-state area Friday.
Near term /through tonight/...
dry air emanating from Canadian high pressure to our north has
allowed for sunny skies as of late Sunday afternoon in most areas.
This trend should continue into this evening along with
diminishing winds. However...as deep layer ridging moves off to
the east a bit and a weak short wave trough approaches...moistening
easterly flow in the low levels will develop and act to increase
cloud cover once again...especially after midnight. We have slight
chance probability of precipitation mainly for drizzle and mainly across Long Island as
the low levels moisten back up. Most areas will probably remain
dry however. Winds will continue to diminish.
Short term /Monday through Monday night/...
Monday should be decent with continued diminishing winds. Any
morning clouds should thin to at least partly sunny skies by late
morning or early afternoon. However...the presence of low level
moisture should keep it from being completely sunny. Temperatures
will once again rise well into the 60s.
A weak short wave trough moves through Monday night with little
fanfare. In fact...the column should be dry enough for mostly
clear skies. Winds will be light.
Long term /Tuesday through Sunday/...
the upper level flow at the beginning of the long term will be
characterized by northwesterly flow. Surface high pressure will
remain in control on Tuesday...but weaken through the day. A
northern stream shortwave will pass to the north on Tuesday night
into Wednesday. The best dynamics will stay near the Canadian
border with this shortwave and with a dry atmosphere...no
precipitation is expected. In fact...skies should be mostly clear.
Ridging builds over the region Wednesday night into Thursday. This
will allow Canadian high pressure to build south over the area.
The pattern is progressive so this ridging and surface high pressure
will quickly move to the east on Friday as a wave of low pressure
approaches from the west. This low is associated with a positively
tilted shortwave trough that should swing through Friday night
into Saturday morning. There are still some differences among the
deterministic and ensemble guidance with this system...but they
have come into better agreement over the last day. The system is
relatively quick moving and originating in the northern stream.
There appears to be a brief window for good moisture advection
ahead of the shortwave and enough lift to produce showers. Have
continued to forecast chance probability of precipitation on Friday into Friday night. The
latest GFS is dry on Saturday...but the 12z European model (ecmwf) run does have
another wave on the backside of this trough moving through late Saturday.
With this in mind...have kept slight chance probability of precipitation on Saturday. High
pressure may build back in on Sunday.
Temperatures will average near normal throughout the long term
Aviation /19z Sunday through Friday/...
high pressure remains north of the area through the taf period.
All the area terminals have become VFR...and should remain VFR
through the early evening. Conditions then return to MVFR as stratus
moves in from the east. The MVFR conditions should remain over the
region through the night...and should start to lift to VFR Monday
morning. Main question is what time the VFR conditions return. For
now...thinking between 12z-15z. Any amendments through the taf
period will be for timing of any MVFR or VFR conditions.
High confidence wind forecast as the north-northeast flow continues.
Speeds will remain 15-20 knots with gusts between 20-25 knots. Gusts
diminish this evening...but should return Monday morning.
Outlook for 18z Monday through Friday...
Monday afternoon...VFR with diminishing NE winds. Gusts will be
less frequent and will be 15-20 knots.
Friday...chance sub-VFR late.
all gale warnings have been converted to small craft advisories as
the winds continue to gradually decrease. Isolated 35 feet gusts
will be possible through the early evening hours on the ocean
waters but not widespread enough to warrant a gale.
Otherwise...Small Craft Advisory conditions are likely to continue over the ocean
waters well into Monday night as seas will be slow to come down as
Joaquin passes well offshore. The sound and bays however should be
below Small Craft Advisory thresholds by daybreak Monday.
With a relaxed gradient over the waters Tuesday through
Friday...winds will remain below Small Craft Advisory levels. Gusts to 20 knots are
possible on the ocean Tuesday morning and then again on Thursday and
Friday. Seas on the ocean will continue to subside Tuesday into the
first half of Wednesday...but will still be above Small Craft Advisory levels. Seas
will subside below 5 feet late Wednesday and remain below Small Craft Advisory levels
mainly dry through at least Thursday.
high tide has passed on the South Shore of Long Island and The
Harbor. The departure was 2.3' at Freeport with most other
locations in the 1.5-2' range. High tide at Lindenhurst is just
after 4 PM with about 1.75 of surge. That places them just below
moderate levels. With the NE flow diminishing and astronomical
tides lowering...current advisories will be allowed to expire with
no new advisories needed. The Great South Bay though could still
come close to minor tomorrow afternoon and would suspect a
statement would suffice. All guidance supports this.
A high surf advisory for the South Shore of Long Island remains
in effect through Monday. Expect beach erosion and washover to
occur due to rough seas and battering waves...with surf as high as
8 feet in spots. A long period swell of 12 to 15 seconds is
contributing to the higher seas.
Waves diminish by Tuesday.
CT...coastal Flood Advisory until 7 PM EDT this evening for ctz009.
New York...coastal Flood Advisory until 4 PM EDT this afternoon for
Coastal Flood Advisory until 7 PM EDT this evening for nyz071-
High surf advisory until 6 PM EDT Monday for nyz080-081-178-
Coastal Flood Advisory until 6 PM EDT this evening for nyz080.
New Jersey...coastal Flood Advisory until 4 PM EDT this afternoon for
Marine...Small Craft Advisory until 8 am EDT Monday for anz330-335-338-
Gale Warning until 6 am EDT Monday for anz350-353-355.