Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
643 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 Monday/...
mostly clear skies continue across much of the area as drier air
emanated from Canadian high pressure to our north.
However...recent satellite and observations across southeast
Connecticut and southeast Long Island have shown a stratocu deck
moving moving back into the area.
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 continue to increase cloud cover
late this evening and overnight...especially from the city east.
We have slight chance probability of precipitation mainly for drizzle across southern Long
Island as the low levels moisten back up. Most areas will
probably remain dry however. Winds will continue to diminish.
Lows will be in the lower and middle 40s inland to the upper 40s
and lower 50s closer to the coast.
Short term /Monday night through Tuesday/...
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 night 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 /00z Monday through Friday/...
high pressure remains north of the area through the taf period.
VFR initially...although MVFR clouds should move in from the east as
the evening progresses...with Long Island and southeast CT terminals the
most likely to experience MVFR ceilings overnight. For terminals
north and west of NYC...VFR conditions expected with few to scattered
Any lower clouds around 2 to 3 kft will lift around the 12-14z time
frame Monday morning...except possibly a little longer eastern
VFR during the afternoon as clouds scatter.
Wind forecast...northeast winds this evening should back slightly to
the north/northeast overnight and continue through the day Monday.
An occasional gust is possible tonight for coastal terminals. More
frequent gusts are expected Monday morning...but winds should
diminish somewhat during the afternoon.
Outlook for 00z Tuesday through Friday...
Monday night...VFR with diminishing NE winds.
Friday...chance sub-VFR late in showers.
winds will continue to gradually diminish overnight. 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 and all coastal flood advisories have been
cancelled. No new advisories needed will be needed as we should
fall short of minor coastal flooding benchmarks with high tide
cycles on monda. The Great South Bay though could still come
close to minor tomorrow afternoon and a statement may be needed.
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.
New York...high surf advisory until 6 PM EDT Monday for nyz080-081-178-
Marine...Small Craft Advisory until 4 am EDT Monday for anz330-335-338-
Small Craft Advisory until 6 am EDT Tuesday for anz350-353-355.