000
FXUS61 KOKX 212003
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
403 PM EDT Wed Jun 21 2023
.SYNOPSIS...
-- Changed Discussion --
High pressure remains over the Gulf of Maine, slowly sliding
out into the open Atlantic through Thursday ahead of an
approaching warm front. Low pressure over the midwest meanders
toward the northeast and weakens on Friday as frontal boundaries
remain nearby through Sunday night before dissipating. Another
frontal boundary approaches for Monday, but this will also
remain nearly stationary through the middle of next week.-- End Changed Discussion --
&&
.NEAR TERM /THROUGH THURSDAY/...
-- Changed Discussion --
Upper ridging remains strong across southern Canada into New
England, while an anomalous and large closed upper low spins
across the southeastern US/Tennessee River valley with a
sheared out vort axis rotating around it up the coast. Deep
southerly flow ahead of this low will have a weak low pressure
wave and warm front riding up the Mid Atlantic coast towards the
region tonight.
This set-up will have stratiform rain gradually overspreading
coastal portions of the region tonight in association with
approaching low/mid level frontogenetic zone and easterly jet.
There are competing factors in terms of determining rainfall
amounts tonight into Thursday, manifesting in quite a spread of
rainfall amounts. In favor of moderate to locally heavy rain is
strong theta-e advection, relatively strong llj for June, PWATS
increasing to 1 1/2 to 2", and increasing warm rain processes
as warm cloud layer increase to 10-12 kft. On the other hand,
factors against are initially dry mid levels and subsidence, and
models indicating the approaching surface wave/warm front will
be weakening, along with its associated llj and frontogenetic
forcing.
Have leaned towards the heavier rainfall scenarios, as this
suite of guidance has better initialized the strength of the
llj this far north and northward extent of rainfall this
afternoon into Central NJ (ECMWF, GFS, NAM 3km). Exact axis of
heavy rain is a bit uncertain, associated with evolution of
easterly jet and position of coastal front. Greatest consensus
appears to be across LI and possibly into SW CT (with
orographics) late tonight thru early Thu aft. Elsewhere,
generally a light to moderate rainfall late tonight into early
Thu afternoon.
Winds may slacked a bit this evening as surface ridging noses
over the local areas, but breezy conditions expected to resume late
tonight into Thu aft between new England high and approaching
mid Atlantic low pressure wave. A modest ENE winds of 15 to 20
mph with gusts 25-30 mph along the coast. A few gusts up to 35
mph are possible Thu am. Winds gradually subside Thu afternoon
as high pressure continues to depart.
Lows tonight will range from the lower to mid 50s inland, to
around 60 for city/coast. Highs on Thursday will be well below
seasonable (about 15 degrees below), generally holding in the
mid 60s.-- End Changed Discussion --
&&
.SHORT TERM /THURSDAY NIGHT/...
-- Changed Discussion --
Anomalous large closed upper low slowly lifts towards Ohio
Valley, with with its sheared out vort axis lifting north of
the region.
Surface warm front approaches, while baroclinic zone lifts
north Thu evening. Although forcing will be weakening,
saturated low and mid levels will maintain cloudy and drizzly
conditions.
Potential for next shortwave to approach towards Fri AM, which
would invigorate shower activity and possibly embedded tsra
ahead/along warm front.
Warmer and moist air advecting in will have temps nears
seasonable.-- End Changed Discussion --
&&
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
The long term will continue to be characterized by a blocky pattern
atypical of mid to late June for this part of the country. A cutoff
low over the mid-West will slowly meander toward the Northeast and
remain somewhere over the Northeast through the weekend, weakening
as it does so. With surface high pressure well off the East Coast
and the weak surface low to our west, a southerly flow develops,
bringing in a stream of moist air which can be traced to the Gulf of
Mexico. Through the weekend, models continue to show PWAT values of
between 1.75" to just over 2.00". With frontal boundaries nearby
providing some lift, southerly flow providing warm and moist air,
combined with the persistence inherent with a blocked pattern, a
prolonged period of precipitation is expected. While a washout is
not expected, there does appear to be more in the way of rain than
dry periods for now. And, in fact, there is the potential for minor
urban and poor drainage flooding, and the possibility of flash
flooding cannot be ruled out at this point, especially with any
areas that receive thunderstorms, putting their rainfall totals
closer to the 2.00" range previously mentioned. This would be in
addition to any rain previously received Wednesday night into
Thursday night. The Weather Prediction Center has placed the entire
forecast area in a marginal risk of excessive flooding for Friday,
with the marginal risk limited to north and west of New York City
for Saturday and Sunday. The CSU-MLP shows a 15-40% of exceeding
flash flood guidance for Sunday (higher probabilities away from the
coast), with 5-15% chance for much of the rest of the area for
Saturday and Monday.
Thereafter, a brief respite is possible for Sunday night into Monday
morning (though there is still a slight chance to a chance for
showers and thunderstorms) before the approach of another frontal
system and upper level trough from the west for Monday. This system
could remain nearby through the middle of the week, though there are
some model differences with how progressive this next frontal system
is, with the GFS being the typically more progressive solution.
Though conditions look to be humid for much of the long term,
temperatures will be held down during the day thanks to clouds and
rain, and should be near normal for this time of year, in the upper
70s to lower 80s.-- End Changed Discussion --
&&
.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
High pressure anchored off the New England coast will drift
eastward as low pressure and an attendant warm front lift
northward into the Mid Atlantic region.
In between these two systems, E winds have increased to 15-20
kt with infrequent gusts to 20-25 kt at terminals closest to the
coast, while inland terminals are mostly sustained 10-15 kt
with gusts mostly just under 20 kt. Winds should diminish a
little toward evening, then back more to the NE and increase
again to these same values late tonight and continue into Thu
morning, with gusts more frequent than has been the case today
so far.
Rain will be moving in late tonight into Thu morning as well,
reaching the NYC metros and Long Island some time between
06Z-09Z, and KSWF/CT terminals by 12Z-13Z. MVFR cond should hold
off for a couple of hours, mostly not coming in til daybreak. An
axis of heavier rainfall may develop and bring IFR cond to KISP/KBDR
by afternoon.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
No unscheduled AMD expected.
OUTLOOK FOR 18Z THURSDAY THROUGH SUNDAY...
Thursday afternoon: Showers. MVFR expected, IFR possible. E
winds G15-25kt along the coast.
Friday through Monday: Showers/MVFR likely, with chance of
tstms/IFR. Best chance for tstms will be from the NYC metros
north/west each afternoon and evening.
Detailed information, including hourly TAF wind component
forecasts, can be found at: https:/www.weather.gov/zny/n90
&&
.MARINE...
-- Changed Discussion --
SCA gusts may weaken a bit across LI Sound and nearshore bays
this evening as upper ridging briefly noses in, but these winds
are likely to resume late tonight into Thursday afternoon, with
easterly gradient tightening between mid Atlantic low and
slowly departing New England high. SCA continues for all waters
into Thu evening. Ideal fetch for seas of 3 to 4 on LI Sound and
6 to 9 ft on the ocean. Winds gradually subside below SCA late
Thu into Thu eve, with ocean seas gradually following suit.
Winds and seas are expected to fall below SCA levels Friday and
Saturday as weak low pressure remains in the vicinity. Waves
may approach 5 ft on the ocean waters Sunday afternoon into
Sunday night for the central and eastern ocean zones, but may be
limited to a small portion of the outer waters of these marine
zones. The eastern ocean zone is more likely to reach 5 ft or
higher late Sunday night. There is a higher chance for both
these zones Monday afternoon.
Winds look to remain below 25 kt through the long term, but may
approach 25 kt on the ocean waters late Monday into Monday night as
the southerly flow increases with the approach of the next frontal
system.-- End Changed Discussion --
&&
.HYDROLOGY...
-- Changed Discussion --
A widespread 1/2 to 1" of rainfall is likely across much of LI
and S CT, with 1/4 to 1/2" of rain elsewhere. A narrow axis of 1
1/2" is possible where coastal front sets up. The probability
of 1"/3 hr is low in this stratiform rain environment, and with
antecedent dry conditions, not expecting any flooding concerns
even if higher amounts are realized.
The Weather Prediction Center has placed the entire forecast area in
a marginal risk of excessive rainfall for Friday and western
sections of the forecast area (the Lower Hudson Valley and northeast
New Jersey) in a marginal risk for Saturday and Sunday. As a more
humid air mass works into the region, PWAT values may rise to 1.75"
to just over 2.00". Any locations in the aforementioned areas could
see up to 2.00" of rainfall in a short period of time. However,
there is a great deal of uncertainty as to certain features that
would be the focus of the development for thunderstorms, such as the
upper low, its surface reflections, and frontal boundaries.
Therefore, even areas outside of the aforementioned locations may
see heavy rainfall, but at this time, the potential is lower than
where there is currently a marginal risk.-- End Changed Discussion --
&&
.TIDES/COASTAL FLOODING...
-- Changed Discussion --
Water level may approach the minor flood thresholds along the south
shore bays on Nassau County with the strong easterly flow w/ tonight
high tide, but expected to stay just below. Some splashover
bulkheads and onto piers is possible though for areas facing the
open bay waters.
There is a high risk of rip current development for all ocean
beaches thru Thursday with building easterly wind swell. Breaking
surf likely builds to 5 to 7 ft with a strong e to w longshore
component, which will likely also enhance beach erosion.-- End Changed Discussion --
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...High Rip Current Risk through Thursday evening for NYZ075-080-
081-178-179.
NJ...None.
MARINE...Small Craft Advisory until 8 PM EDT Thursday for ANZ331-332-
335-338-340-345.
Small Craft Advisory until 8 AM EDT Friday for ANZ350-353-355.
&&
$$
SYNOPSIS...JP/NV
NEAR TERM...NV
SHORT TERM...NV
LONG TERM...JP
AVIATION...BG
MARINE...JP/NV
HYDROLOGY...JP/NV
TIDES/COASTAL FLOODING...NV