Scientific Forecaster Discussion
fxus61 kokx 170545
Area forecast discussion
National Weather Service New York New York
1245 am EST sun Nov 17 2019
the center of strong high pressure shifts through northern New
England overnight and Sunday, then moves offshore Sunday night.
Coastal low pressure approaches on Sunday night and passes to
our southeast on Monday. A second weaker system is expected to
develop well offshore Tuesday night and move away during
Wednesday. High pressure will build by Wednesday night and
settle nearby on Thursday. A cold front will move through on
Friday followed by high pressure to begin next weekend.
Near term /until 6 am this morning/...
high pressure centered over northern New England shifts slowly
eastward overnight. Meanwhile, low pressure off the Carolina
coast shifts NE. The pressure gradient between the two systems
will maintain somewhat breezy conditions, and models agree with
low level moisture/clouds beginning to move in towards the coast
towards daybreak. Scattered light rain over southern New Jersey
and off the coast and into the Delmarva may also move northward
toward Long Island toward daybreak, as some of the hi res
models indicating. For now, high pressure continues to hold the
majority of the clouds and precipitation off the mid Atlantic
coast at Bay. A few high clouds expected across the area
through much of the overnight period. Regardless of how far the
clouds progress and breezy conditions, low temperatures will
still be about 10 degrees below normal in this cold air mass.
Made minor adjustments to temperatures, dew points, and winds,
otherwise the forecast remains on track.
Short term /6 am this morning through 6 PM Monday/...
high pressure moves across northern New England on Sunday while
the coastal storm off the Carolinas continues its path NE.
Lower level clouds will continue to push north through the
forecast area although areas northwest of the city could end up with at
least partial sunshine for a good portion of the day. Moisture
will still be shallow through the day, confined to below 875mb.
Lift will be weak at best, so will go with a dry forecast. High
temperatures will be a little warmer than it was was today, but
still around 10 degrees below normal.
The coastal low begins to travel in a more northerly direction
Sunday night as the associated cutoff low begins to interact
with an approaching longwave trough from the west and upper
ridging weakens over US. Still some model spread regarding
timing and northwest progression of pcpn, but overall it appears that
it eventually becomes likely east NYC with chance pops to the
west. Rain will be the precipitation type for most areas. For some of the
northern zones, whether it be too warm of an elevated warm nose
aloft or a lack of moisture in the dendritic growth zone,
profiles would likely preclude the possibility of snow. This
leaves the potential of freezing rain and maybe even some sleet
for these areas, but with pops only at chance here, will hold
off on issuing any advisories.
The storm center then passes southeast of the 40n/70w benchmark on Monday.
Rain likely for most areas in the morning. Rain chances then
diminish somewhat in the afternoon, but is still likely over CT and
Winds with this storm will be strongest late Sunday night through
Monday morning. Coastal sections during this time will have NE winds
20-25 mph with gusts up to 30-35 mph.
Long term /Monday night through Saturday/...
it will be a progressive long wave pattern during the period.
The eastern US trough will redevelop sort to speak Monday night
with mean upper level troughing through Tuesday night. In the
wake of low pressure in the short term period, moisture will be
lacking in the mid levels. Therefore precipitation chances will
generally lower Monday night into Tuesday. The only fly in the
ointment is with a vort Max rounding the trough which will have
some good positive vorticity advection with it towards and after midnight late Monday
night and into early Tuesday morning. Guidance continues to hint
at the potential for measurable precip for northwestern zones
during this time frame as temperatures begin to cool. For the
time being straying away any measurable frozen precip for far
northwestern zones, but it will be close. Precip amounts would
be very light if it does in fact take place. This will have to
be monitored with subsequent forecast cycles as surface
temperatures in these areas get close to freezing early Tuesday
morning. With mean upper level troughing in place and a surface
trough nearby think it is prudent to maintain at least slight
chance pops into early Tuesday morning for the remainder of the
area. With all profiles above freezing any light or showery
precip would be in the liquid form, even well inland later in
the morning. Despite a good deal of clouds during much of
Tuesday, much of the day should go by generally dry with cool
advection aloft beginning to take hold. This along with a lack
of mid level moisture should limit precipitation despite the
clouds Tuesday and Tuesday night. Overall there will be a lack
of meaningful synoptic scale lift despite the upper level trough
being in place. A storm system will develop well offshore for
Tuesday night into Wednesday morning in response to the actual
upper level low, but will develop too late and too far to the
east and northeast to impact the region.
The 500 mb trough axis then pivots through by 12z Wednesday
morning, followed by transient height rises and ridging late
Wednesday into Thursday. This will lead to high pressure
building in at the surface from the southwest on Wednesday, with
dry conditions expected during the day Wednesday through the
day on Thursday. The baroclinicity and colder air will be
lacking with this high pressure system, therefore temperatures
are expected to average near normal for the mid week.
By Thursday night a northern branch shortwave will dive into
the upper Midwest and Great Lakes. This will translate east and
drag a cold front through the region during Friday. The timing
of the front is difficult, but appears to be more likely during
the first half of Friday. Chance pops for late Thursday night
into much of the first half of Friday seems prudent at this
time. A broad West Coast ridge and broad eastern US trough then
is forecast to follow into next weekend. The source region will
not be nearly as cold as previous high pressure systems,
therefore temperatures should be somewhat seasonable into next
weekend despite the mean upper level trough into the northeast.
Aviation /06z Sunday through Thursday/...
high pressure over New England will move east into the Canadian
Maritimes on Sunday as low pressure off the southeast coast
gradually drifts northward.
VFR with only a few high clouds overnight. Cigs in the 035-040
range encroach from the south Sunday morning, lowering to MVFR
at the NYC Metro and coastal terminals between 13z-16z. Rain
will also begin to overspread the coastal terminals toward
daybreak Monday, with continued MVFR conditions.
Winds remain north/NE through the period. G20-25kt should return
after 14z and continue through the rest of the taf period.
Outlook for 06z Monday through Thursday...
late Sunday night and Monday...IFR conditions are possible
late Sunday night/Monday morning as rain develops, otherwise
MVFR. A brief period of freezing rain is possible at kswf if
precipitation develops early enough. NE winds g20-25kt.
Monday night and Tuesday...mainly VFR.
Wednesday...VFR. Northwest winds g15-20kt.
winds are expected to increase overnight in response to a re-
tightening pressure gradient ahead of an approaching coastal
low. The low will pass southeast of waters on Monday. Gales are
expected on the ocean into Monday, with Small Craft Advisory conds lasting
through Monday on the rest of the waters. Ocean seas eventually
build up to 10-15 ft late Sunday night into Monday morning.
Winds will continue to decrease Monday night with the non-
ocean waters having sub Small Craft Advisory conditions. Out on the ocean seas
will be decreasing, but will still remain elevated through
Monday night and into a good part of Tuesday. Therefore Small Craft Advisory
conditions due to elevated seas will likely continue into
Tuesday out on the ocean. Sub Small Craft Advisory conditions will continue for
all waters late Tuesday through early Wednesday, with marginal
Small Craft Advisory conditions possibly returning out on the ocean late
Wednesday due to 4 to 5 foot seas as a northwest wind increases
late due to a tightening pressure gradient due to building high
no hydrologic impacts are anticipated through the forecast
update was to convert the coastal Flood Watch to a coastal Flood
Warning for the Sunday high tide cycle for those South Shore Back
Bay locations of Nassau and southwest Suffolk.
However, expected tide levels were lowered slightly across the board
for the Sunday and Monday high tide cycles per latest guidance and
overall synoptic evaluation of storm, wind, etc. Fairly large spread
in ensemble guidance is noted, which leads to lower confidence in
exact tide level forecasts.
This timeframe is between full and new moons, which has helped as
large tidal departures are needed for coastal flooding due to
relatively low astronomical tides.
1-2 ft foot departures are needed for minor thresholds, and 2 to 3
ft is needed for moderate during the day. At night, astronomical
tides are about a foot lower, so only localized moderate coastal
flooding would be possible, with areas of minor and some locations
likely falling short of minor coastal flood benchmarks at night.
All of this is due to prolonged east-NE ocean gales through
Monday, accompanied by long period easterly swells of 9-13 ft by
Sunday, and 10-15 ft on Monday. Winds do back to the north
Sunday night and Monday which may help keep departures down
somewhat in spots (areas where northerly winds push water away
from the shoreline).
Elevated water levels with 8-12 ft breakers along the ocean
beachfront will result in beach erosion and flooding, with areas
of dune erosion and localized washovers likely during the times
of high tide Sunday into Monday. The North Shore of Long Island
and the north facing shoreline of the South Fork will also
likely have beach erosion and localized wave splashover issues
due to rough waves as well.
Perhaps some South Shore Back Bay locations may still hover at
or just below minor coastal flood benchmarks for the Monday
night high tide cycle. Otherwise the threat for coastal flooding
will generally subside Monday night into Tuesday.
NYC National oceanic and atmospheric administration weather radio station kwo35 (162.55 mhz) is operating
at reduced power until further notice.
CT...coastal flood advisory from noon today to 4 PM EST this
afternoon for ctz009-010.
New York...coastal flood advisory from 9 am this morning to 1 PM EST this
afternoon for nyz072-074-075-178.
Coastal flood advisory from noon today to 4 PM EST this
afternoon for nyz071-073-078-176-177.
Coastal Flood Warning from 9 am this morning to 3 PM EST this
afternoon for nyz080-179.
Coastal Flood Watch from this afternoon through Monday
afternoon for nyz080-179.
Coastal flood advisory from 11 am this morning to 5 PM EST
this afternoon for nyz079-081.
New Jersey...coastal flood advisory from 9 am this morning to 1 PM EST this
afternoon for njz006-106-108.
Marine...Small Craft Advisory until 6 PM EST Monday for anz330-335-338-
Gale Warning until 1 PM EST Monday for anz353-355.
Gale Warning until 6 PM EST Monday for anz350.