000
FXUS61 KOKX 272139
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
539 PM EDT Sun Sep 27 2020
.SYNOPSIS...
Weak low pressure passes nearby tonight. A slow moving frontal
system then approaches from the Ohio Valley on Monday and
Tuesday, moving across the area Wednesday into Wednesday night.
Waves of low pressure will move along the frontal boundary, bringing
an extended period of unsettled conditions. A series of reinforcing
cold fronts will then follow at the end of the week with high
pressure returning next weekend.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Warm advection light showers ahead of a weak low pressure
circulation continue to track north towards Long Island.
Initial band of these showers weakened somewhat as they moved
onshore, but another band is approaching. This process will
continue through this evening with scattered showers across the
area tonight due to a combination of the weakening low pressure
nearby and PVA ahead of a shortwave approaching from the Mid
Atlantic.
Rainfall will be on the light side - possibly in the
form of drizzle. Any fog will probably be on the lighter side
and just patchy as suggested by turbulent mixing parameters in
forecast soundings. The clouds and dewpoints in the 60s will
help keep low temperatures 10-15 degrees above normal.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
The shortwave shifts through the forecast area during the day
Monday. Not as significant, but still present, is lift from a weak
jet streak aloft. Cannot rule out showers at any given point of the
day, but overall probably less of a chance towards late in the day
as the sources of lift exit. Moisture is still shallow, so any
shower activity will probably be light in intensity.
The high temperature forecast is a little challenging due to
uncertainty surrounding how much the cloud cover dissipates during
the afternoon. Thinking it will be similar to Sunday afternoon where
it`s partly to mostly cloudy with the higher cloud cover east of the
city. Temps aloft will not have changed all that much as well. NBM
was used for high temps, which best matches this thinking.
Lift remains on the weak side through Monday night, but will
increase from the west late at night as PVA increases ahead of an
approaching shortwave. Low chances of showers, and once again,
patchy fog development.
There is a moderate risk of rip currents at the Atlantic Ocean
beaches on Monday due to a building southerly swell and
strengthening onshore winds.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
An unsettled Tuesday through the end of the week continues to become
more likely as deterministic models and ensembles slowly come into
better agreement. Differences arise with timing of specific
features, but overall much needed rainfall is becoming likely
Tuesday through early Thursday morning.
A longwave trough over the eastern CONUS with two separate
shortwaves, one within the northern stream and one in the southern
stream, will help draw up tropical moisture from the Atlantic and
Gulf of Mexico. The longwave trough will only slowly pivot towards
the east coast Tuesday into Wednesday, but will send a cold front
towards the region. Several waves of low pressure will ride along
the front, with the first coming late Tuesday through Wednesday
morning. This wave will largely be associated with the northern
stream trough and will help send the cold front into the region. The
cold front then is likely to stall over or just to our east late
Wednesday into Wednesday night. At the same time, the southern
stream shortwave energy will quickly lift northward. This depicted
by the GFS and ECMWF, which develop a deepening wave of low pressure
that lifts along the Middle Atlantic and northeast coast into
Thursday morning. However, there are some deterministic models (CMC,
ICON) and members of the GEFS that are much quicker/drier. A blend
of the GFS and ECMWF were used in this forecast as they have been
the most consistent the last several runs.
The most significant rain is expected late Tuesday into Wednesday
morning and then again Wednesday night. Showers on Tuesday are
likely to be associated with warm advection and increasing low level
flow. More organized rain showers will then become widespread as
large scale lift maximizes over a tropical air mass. Showers should
diminish in coverage, and possibly end for a time later Wednesday
afternoon before becoming widespread again with the second wave of
low pressure Wednesday night. Conditions should dry out Thursday
morning as the energy and low lift quickly to the northeast.
Rainfall amounts are a bit challenging as the placement of heaviest
rain is still in question. Three quarters to an inch and a half is
forecast Tuesday through Wednesday morning. Another inch to inch and
a half is possible Wednesday night with a total on average around 2
inches. Locally higher amounts are possible in heavier rain. Due to
the long duration of the event as well as very dry antecedent
conditions and high flash flood guidance values, no significant
flooding is anticipated. Minor urban and poor drainage flooding
would be the main concern. There is some CAPE on soundings Tuesday
afternoon/evening away from the coast, so have mentioned thunder
here. Otherwise, have kept thunder out of the forecast.
Dry conditions briefly return late Thursday morning through Friday
morning. A series of secondary cold fronts will move through the
region. The longwave trough will also remain in place across the
eastern states with its axis to our west. There are hints at another
vort max within the trough moving towards the region on Friday. This
energy may act upon the baroclinic zone just offshore to develop
another low pressure. Differences are quite high among the guidance
in its location and whether it develops offshore or closer to the
region. Have capped PoPs off at chance for the eastern half for now.
High pressure then builds into the weekend.
Above normal temperatures Tuesday and Wednesday will trend to near
seasonable levels Thursday and Friday. Below normal temperatures are
then expected next weekend.
There is a high risk of rip currents at the Atlantic Ocean
beaches on Tuesday due to a southerly swell and strengthening
onshore winds.
&&
.AVIATION /22Z SUNDAY THROUGH FRIDAY/...
Area of high pressure over the Atlantic maintains the
persistent flow. Low pressure approaches from the west late
Monday.
Light east to southeast winds will gradually become more
southerly near sunrise but remain around or under 10kts.
MVFR conditions will likely become IFR tonight. All areas are
expected to drop to IFR tonight from a combination of low
ceilings and patchy fog. ISP and GON in particular will have to
be monitored for LIFR possible overnight.
Could see scattered showers and drizzle overnight with
additional showers possible over the Lower Hudson Valley
terminals Monday.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Low ceilings possible again tonight. Timing may require
amendments.
.OUTLOOK FOR 18Z MONDAY THROUGH THURSDAY...
.Monday...Chance of IFR/MVFR conditions. Chance of showers,
mainly during the day.
.Tuesday...Chance of IFR/MVFR conditions. A chance of showers. A
slight chance of thunderstorms. S-SW wind gusts around 20 kt.
.Wednesday...IFR/MVFR with showers likely. SW wind gusts
15-20kt day into early evening.
.Thursday...Chance of MVFR. Chance of showers. SW wind gusts
15-20kt day into early evening.
.Friday...VFR. W winds less than 15kts. Afternoon showers
possible.
Detailed information, including hourly TAF wind component
forecasts, can be found at:
http:/www.weather.gov/zny/n90
&&
.MARINE...
Swells have increased on the ocean a little more than guidance, so
will go with a SCA for elevated seas east of Fire Island Inlet
tonight through Monday. It is possible however that waves are
averaging below 5 ft across most of the zones at times. More
confidence in waves staying below 5 ft Monday night. Winds now
through Monday night will be on the lighter side, generally around
10 kt and onshore.
Seas build on the ocean Tuesday ahead of a slow moving cold front.
Seas should then will be around or just above 5 ft Tuesday night and
continue to build through Wednesday. Winds may also gust to around
25 kt Tuesday night into Wednesday as the cold front nears the
waters. SCA conditions may also occur late Wednesday night into
Thursday on all waters as low pressure and the cold front move
across the waters. Ocean seas may remain elevated through Friday,
but winds should remain below 20 kt Thursday night into Friday.
&&
.HYDROLOGY...
A slow moving frontal boundary and several waves of low pressure
will bring a significant rainfall Tuesday into early Wednesday and
then again Wednesday night into early Thursday. Total rainfall
amounts average around 2 inches with locally higher amounts
possible. Due to dry antecedent conditions, the long duration of the
event, and high flash flood guidance, no significant flooding is
anticipated. Minor urban and poor drainage flooding is the main
threat.
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
NJ...None.
MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ350-353.
&&
$$
SYNOPSIS...JC/DS
NEAR TERM...JC/DS
SHORT TERM...JC
LONG TERM...DS
AVIATION...DJ
MARINE...JC/DS
HYDROLOGY...JC/DS
NWS OKX Office Area Forecast Discussion
