Scientific Forecaster Discussion
fxus61 kokx 221220
Area forecast discussion
National Weather Service New York New York
720 am EST sun Jan 22 2017
a stationary front will remain off the southern mid Atlantic coast
today, with areas of weak low pressure riding east along it.
Meanwhile, another low will move across the southern states today,
and intensify into a major coastal storm tonight into Monday,
while high pressure builds southeast into New England. This
combination will produce very strong east winds from late tonight
into Monday night. The low will pass over or just south and east
of the coastal waters on Tuesday. High pressure will build in the
wake of the storm on Wednesday. A cold front will then slowly
approach from the west and move through on Thursday.
Near term /until 6 PM this evening/...
cancelled dense fog advy as vsbys have lifted in most places,
except perhaps right along immediate south facing coastlines.
Widespread fog was across the region as a saturated air mass under
an inversion remains into early morning. At the upper levels
weak ridging moves east.
Skies should remain cloudy this afternoon as a weak low moves
along a stationary front off the Delmarva coast. Some associated
light rain possible this afternoon, especially late, as ridging
aloft finally beings to move east.
Short term /6 PM this evening through Tuesday/...
significant coastal storm expected late tonight into Tuesday with
high winds, heavy rain, and coastal impacts.
A closed low over the Southern Plains will continue to intensify
and move east to the southern mid Atlantic region on Monday. The
eventual result will be a strong surface low developing over the
southeast states Sunday night and riding up the coast through
Monday, reaching a position just south of Long Island by late
Monday night. The low will interact with high pressure building
south from Quebec to produce a very tight pressure gradient and
long easterly fetch from south of Newfoundland. Model spread is
closing with regard to timing of the strongest winds and heaviest
rain, with the strongest winds expected Monday afternoon and
Strong winds...upgraded coastal areas to a High Wind Warning for
high confidence in sustained 30-40 mph with gusts 60-70 mph.
Highest winds expected across Long Island, particularly on the
east end and along the South Shore. This based on excellent
potential for downward momentum Transfer of a 70-75 kt 950-975 mb
low level jet via both mixing in either a well-mixed or moist absolutely
unstable boundary layer. The storm also presents high potential
for a Gravity wave event to unfold and enhance downward momentum
Transfer, as a highly unbalanced/ageostrophic upper level flow
develops in the exit region of an intense upper jet streak moving
up the coast, with large duct function values present in the low
levels over and just south of the County Warning Area.
Precipitable water of 3-4 Standard deviations above avg continues to be signaled.
Coastal front development and orographic lift over eastern faces
of hilly terrain will be favored for the heaviest rainfall.
Embedded convection not out of the question late Monday/Mon eve
ahead of approaching closed low and with warm conveyor belt
feeding into the region. Based on ensemble/operational output,
expect rainfall of 1-3 inches with locally higher amounts.
Models still indicated low-level cad under an 700 mb-8 warm nose late
tonight through Monday afternoon over the region. Based on strong
dynamics and a deep enough cold layer well northwest of NYC Mon, should
see a prolonged mix of sleet and rain well northwest of NYC through the
day on Mon mainly across Orange/Putnam/W Passaic, where up to an
inch of accumulating sleet is possible, with lower amounts across
interior SW CT along/north of I-84.
Winds and heavy precip should fall off later Mon night from wet-
east as the low level jet moves NE...but how quickly is still in question.
The slow moving storm will pass on Tuesday. With the associated
upper level low remaining over the region, will continue to
mention likely/Cat pop mainly in the morning.
Long term /Tuesday night through Saturday/...
rain chances should gradually diminish through Tuesday night.
Generally looking at mostly dry conditions Wednesday through
Saturday. A cold front will bring cooler conditions for the end of
the long term period.
Expect highs Tuesday through Thursday in the middle and upper 40s, a
good 10 degrees above normal. Friday and Saturday, high temperatures
fall back to near normal, with high in the upper 30s and lower
Aviation /12z Sunday through Thursday/...
weak low pressure rides along a stationary front to the south
today. A coastal storm then approaches tonight.
Widespread IFR to LIFR conditions will persist through
13-16z. Conditions begin to improve around 15-16z, with MVFR
conditions possible by that time. Timing is uncertain at this
time, and there is a chance IFR conditions remain into the
afternoon. With the approach of the low from the south tonight,
rain becomes likely later this evening and overnight.
Light winds initially become east to northeast, 5 to 10 knots. Winds
increase through the day, to near 15 knots with gusts 20-25 knots
this evening. Winds increase further late tonight.
Outlook for 12z Monday through Thursday...
Monday-Monday night...IFR in rain and fog. Low level wind shear. Rain and sleet at
kswf. East-NE wind 25-35 knots g40-50kt, occasional higher gusts near the
Tuesday-Tuesday night...rain tapering off by afternoon with
improving ceilings into the evening. Northwest winds g25-35kt, highest in
Wednesday and Thursday...VFR. SW winds 15-25 kt.
dense fog remains across the forecast waters through the morning.
An intensifying storm moving up the coast will bring hurricane
force wind gusts to the ocean waters Monday into Monday evening
and possibly even the eastern sound/bays Mon evening. Ocean has
been upgraded to a hurricane force wind warning, while storm
warnings remain in effect for the remaining waters, with peak
winds 50-60 kt expected. Before then, gales are likely to develop
quickly tonight, followed by storm force winds developing from
south to north through the day on Mon.
Max seas could peak at 20-22 ft on the ocean, 9-12 ft from Orient
Point east, and 8-9 ft on central Long Island Sound, per combo of
wavewatch/nwps guidance and wind/wave climatology.
Winds start to diminish on Tuesday, however there could be a
period of northwest gales on the back side of the storm late day Tue into
Tue evening on the ocean. Ocean seas will also take quite some
time to fall below 5 ft thereafter.
quantitative precipitation forecast late tonight into Monday will likely be in the 1-3 inch
range, with locally higher swaths possible with the heaviest
rainfall Mon afternoon/eve. If high end rainfall amounts are
realized, this will bring a threat for moderate urban flooding
and minor small stream flooding in NE New Jersey and the lower
Hudson Valley. This would be exacerbated by coincidence of high
tide with the heavy rain Mon eve. Potential for minor flooding on
larger rivers is slight.
a strong coastal storm will impact 2 successive high tide cycles of
at least minor coastal flooding. The first tide cycle to be impacted
is late tonight into early Monday morning. Minor coastal flooding is
expected in spots as astronomical tides run a little higher than the
late afternoon/evening tides. East/northeast winds are increasing
during this time, but will not be quite at their peak.
Expect the lower New York Harbor areas to experience minor coastal
flooding, along with the South Shore and eastern bays of Long
Island, and western Long Island Sound.
Then, attention turns toward the next high tide cycle late Monday
afternoon/evening. Potential for moderate coastal flooding for
southern and eastern bays and beachfront communities of Li with this
Monday evening high tide, and widespread minor coastal flooding
The moderate coastal flood potential will increase if the slower
coastal low movement (stronger east/NE winds Mon evening) comes to
fruition...with even a low potential for major flood thresholds to
be reached in the most vulnerable communities such as Lindenhurst
and Freeport. A coastal Flood Watch has been issued to address this
moderate flood threat. Minor coastal flooding could linger for the
southern and Eastern Bay areas for the Tuesday morning high tide
cycle as well.
An ensemble of guidances is showing potential for surge to build to
2 to 3 ft Mon am...and 3 1/2 to 4 1/2 ft by Monday evening.
The highest threat for coastal impacts will be for flood prone
locales along the South Shore bays of Li/NYC...eastern bays of
Li...lower New York/New Jersey Harbor including tidally affected rivers...and
western Li sound.
The other concern will be for widespread dune erosion and localized
washovers at Atlantic Ocean beaches from elevated waters levels
and an east to west sweep of 8 to 12 ft surf Mon into Tue.
CT...High Wind Warning from 1 am Monday to 1 am EST Tuesday for
Coastal flood advisory from 6 am to 10 am EST Monday for
New York...High Wind Warning from 1 am Monday to 1 am EST Tuesday for
Coastal Flood Watch from Monday afternoon through Monday
evening for nyz079>081-179.
Coastal flood advisory from 4 am to 8 am EST Monday for nyz074-
Coastal flood advisory from 6 am to 10 am EST Monday for
New Jersey...High Wind Warning from 1 am Monday to 1 am EST Tuesday for
Coastal flood advisory from 4 am to 8 am EST Monday for njz006-
Marine...dense fog advisory until 10 am EST this morning for anz330-335-
Storm Warning from 1 am Monday to 1 am EST Tuesday for anz330-
Hurricane force wind warning from 1 PM Monday to 1 am EST
Tuesday for anz350-353-355.