Scientific Forecaster Discussion
fxus61 kokx 271813
Area forecast discussion
National Weather Service New York New York
213 PM EDT Sat may 27 2017
multiple weak waves of low pressure pass to the south through
Monday, as high pressure gradually builds down from southeastern
Canada. This high retreats to the northeast Monday night. A
series of weak fronts or troughs of low pressure cross the area
Tuesday through Thursday. Weak high pressure then builds in
through Friday, as a front stalls to the south of Long Island.
Near term /until 6 PM this evening/...
a dissipated convective complex will continue to pass just to
the SW/S of the area this afternoon. An isolated shower possible
across NYC Metro and Point North & west due to combined associated
shortwave forcing and weak instability this afternoon.
Highs today will be near normal...generally holding or slowly
falling from the upper 60s along south coasts in wake of sea
breeze. Across NYC/New Jersey Metro and interior lower to mid
70s...before sea breezes marches through.
There is a moderate risk of rip currents at the ocean beaches
today due to residual 3 ft southerly swells.
Short term /6 PM this evening through 6 PM Sunday/...
northern stream 850-500 hpa ridging builds in tonight, as
onshore flow sets up below 900 hpa. Could end up seeing some
patchy drizzle late tonight/into early Sunday morning as a
result. Lows tonight should be a few degrees above normal.
The aforementioned ridge axis transits over the area Sunday,
with moisture trapped under the subsidence inversion making for
a mostly cloudy day. Given expected cloud cover and onshore
flow, did cut back on highs to around 5-10 degrees below normal.
This was based on blending NAM/ecwmf 2-meter temperatures in
with met/ecs guidance and a mix down from 975-925 hpa per BUFKIT
Long term /Sunday night through Friday/...
the northern stream ridge slides offshore Sunday night, allowing
for light rain to overspread most of the area with some modest
isentropic ascent (could remain dry over far eastern portions).
A northern stream shortwave rotates across the area around the
base of a closed low over Ontario/northern Great Lakes Monday.
Even with onshore flow, showalter indices are progged down to -2
to -4 by afternoon in response to fairly steep mid-upper level
lapse rates, have opted for showers, with a chance of
thunderstorms by afternoon. Given showalter indices cannot rule
out some locally strong storms and cannot 100% rule out a
severe cell or two. The main threat would be large hail - with
wet bulb zero heights progged at 8-9 thousand feet late Monday
afternoon/early Monday evening. The marine inversion likely will
prevent any gusts to severe levels.
The showers with embedded thunderstorms should come to an end
from SW to NE Monday night as the shortwave trough exits to the
The closed upper low and longwave trough will be slow to move
east through the middle to late part of next week as a series
of shortwaves rotate through the trough, while at the surface
weak lows, or troughs move through the area. There remains a lot
of uncertainty with the timing and placement of the systems
through the upcoming week. As a result, there could be a
prolonged period of unsettled weather. Will carry slight chance
to low chance probabilities through Thursday, highest over
northern zones, closest to the closed low/any shortwaves
rotating around it. For now have gone with a dry forecast
Thursday night and Friday as the main axis of the opening
closed low is progged to lift to the northeast.
Aviation /18z Saturday through Thursday/...
weak high pressure remains over the terminals today thru Sunday.
VFR. Sea breezes with winds mostly S to southeast at 10 knots or less
today, then light southeast tonight. MVFR cigs late tonight into mid-
Outlook for 18z Sunday through Thursday...
Sunday night...late night MVFR with chc shra/IFR.
Monday...MVFR conds likely and IFR conds possible. Showers
likely and chance of tstms.
Tuesday-Wednesday...mainly VFR. Chance of showers/tstms mainly
northwest of the NYC Metro terminals.
quiet through Sunday night as ocean swells subside and winds
remain light. Southeast winds increasing to 15-20 kt on Mon could
lead to ocean seas reaching 5 ft again Mon afternoon/evening.
Otherwise, outside of any tstms on Monday, winds/seas on the
waters should remain tranquil.
no significant widespread hydrologic impacts are expected
through at least the middle of next week.
the combination of high astronomical tides and southerly swell
will keep water levels within striking distance of minor coastal
flood benchmarks for the night time high tide cycles into
Widespread minor coastal flooding is expected for the high tide
cycle tonight along the South Shore bays of
Brooklyn/Queens/Nassau, also for the shores of
Westchester/Fairfield along western Long Island Sound. A coastal
flood advisory continues. Brief and localized minor coastal
possible for the remainder of the western Li sound...lower New York/New Jersey
Harbor and SW Suffolk.
Tides lower for Sun night high tide...but surge likely increases
a bit with strengthening se flow. The net result...looks to be
potential for additional widespread minor coastal flooding for
the southern bays of western Li...with localized and brief
minor flooding for the remainder of areas that have been
affected over the last several days.
CT...coastal flood advisory from midnight tonight to 3 am EDT
Sunday for ctz009.
New York...coastal flood advisory from midnight tonight to 3 am EDT
Sunday for nyz071.
Coastal flood advisory from 9 PM this evening to 2 am EDT
Sunday for nyz075-178-179.