NYC Office Forecast Discussion

000
FXUS61 KOKX 210008
AFDOKX

Area Forecast Discussion
National Weather Service New York NY
808 PM EDT Sat Jul 20 2019

.SYNOPSIS...
Region will reside between high pressure over the western Atlantic
and a cold front dropping south across eastern Canada. The cold
front will move across the region late Sunday afternoon into
the evening. A wave of low pressure moves along the front
Monday and Monday night as it slowly pushes through the local
area. High pressure then returns for the remainder of the week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Forecast is mainly on track. Isold pulse showers/tstms have
developed just outside of the local forecast area so have
expanded the schc pops a bit this evening. Slight adjustments
also made to T/Td and sky based on current conds and trends.

Otherwise, high heat and humidity will remain the focus into
this evening with much of the region reporting heat indices 100
to 105.

Forecast area will remain at the southern edge of the westerlies
with broad upper ridging across the southern half of the country
merging with the subtropical high over the western Atlantic.
Anomalously warm heights aloft, deep westerly flow, and high
boundary layer moisture (high humidity) will result in dangerous
heat indices through early this evening. Even overnight, the
urban corridor and coastal sections will see heat indices in the
mid 80s to around 90. While there will be some relief overnight,
it will remain a hazard for living premises that are not
ventilated well or do not have AC.

Lows will be in the upper 70s to lower 80s by daybreak. This
almost 15 degrees above normal.

There is a moderate risk of rip currents at Atlantic Ocean
beaches through this evening.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Upper low descending south and east from Hudson Bay will send
height falls across eastern Canada as well as cold front across
the Great Lakes toward the region. Even so, a deep-layered
westerly flow will result in another day of high heat and
humidity with heat indices once again in the 105-110 range.

There are a few wild cards in play that could limit the heat
somewhat. This includes a more westerly flow with the
potential for some drier air aloft mixing down to the surface.
It may be just enough to keep values lower than Saturday.
Additionally, instability clouds ahead of the approaching cold
front and convective debris form upstream may filter into the
region in the afternoon.

Preference at this time was to go on the warmer side of the
guidance. Even if some drier air is realized in the low levels,
this may in fact allow the airmass to heat up further. Much of
the area will see highs in the lower to mid 90s, with readings
near 100 in the urban corridor of NE NJ.

Cold front and pre-frontal trough will move into the area late
afternoon/early evening. While the airmass ahead of it is
clearly hot and unstable, it may be too warm aloft with capping
and not enough forcing to break it. Wind shear is also weak and
not favorable for organized convection. Thus, there are only low
chances for showers and thunderstorms in the forecast.

Cold front moves through in the evening with any showers
pushing to the south. Drier and cooler air will gradually
filter in overnight into Monday morning.

For Sunday at the Atlantic Ocean beaches, there will be a low
rip current risk.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
The period starts with a frontal boundary near the local area. An
upper level trough digging through the Great Lakes and Ohio Valley
Mon/Mon night will spawn a sfc low on this boundary in the Ohio
Valley Sun night and tracking it eastward Mon and through the local
area Mon night. The location of the front and amount of cloud cover
Monday morning will be key in determining the potential for severe
weather as well as high temps. The oppressive heat will be a thing
of the past by Monday, with highs mostly back in the 80s, although
the humidity will remain. SPC has much of the Tri State in a
marginal risk, but this may even be too high. Shear looks to be
high, but instability could be mainly south of the area limiting the
potential for severe weather. Have maintained chc tstms in the
forecast for the entire area, but this too could be overdone and am
not including any enhanced wording at this time.

Will need to monitor the track of the low, with indications of
1/2 to an inch of rainfall falling on the north side of the low
from the combination of frontogenesis and an approaching
entrance region of an upper jet enhancing lift. Storm total
rainfall amounts may range from 3/4 of an inch to 2 inches.
Highest amounts are currently N and W of NYC, but a slight shift
to the SE would bring the highest amounts right over the most
flood prone areas (NE NJ and NYC).

The front sags back to the south on Tue with pcpn ending. The
upper trough will linger through the middle of the week and
could trigger an isold shower Wed aftn as a shortwave moves
through although it will be battling subsidence from
strengthening ridging. Heights will rise through the remainder
of the forecast period, with dry weather and gradually
increasing high temps.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
A couple of isold showers/tstms NW of the NYC metros could
bring brief IFR/gusty winds to KSWF, also brief MVFR to KTEB and
a brief wind shift to the NW at KEWR as an associated weak gust
front passes through. Otherwise, the terminals will reside
between offshore high pressure and a cold front dropping south
across eastern Canada, with the moving across late Sunday
afternoon into Sunday evening.

The high will maintain a general SW-W flow 10 kt or less
tonight, then winds should veer W after 12Z and increase to
10-15 kt with some gusts close to 20 kt in the afternoon. Do
show winds backing more to the SW along the coast in the
afternoon, but there is some uncertainty.

As the cold front approaches, could see sct late day tstms from
the NYC metros north and west.

.OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY...
.Sunday night...Chance of a tstm early with MVFR or lower conds
mainly NYC metros, otherwise VFR.
.Monday and Tuesday...Chance of showers and tstms with MVFR or
lower conds possible at times.
.Wednesday and Thursday...VFR.

&&

.MARINE...
Sub-SCA conditions are expected into Sunday with a prevailing
W-SW flow. Gusts on the ocean waters will approach 20 kt nearshore,
mainly during the afternoon hours. A cold front moves through
late Sunday afternoon into early evening with the potential for
scattered convection. A northerly flow of 5 to 10 kt develops
in wake of the front.

Seas Mon night/Tue appeared to be too high based on the scenario so
have knocked them down around a foot. Thus, have sub-advsy conds
through the remainder of the period with a relatively weak flow.

&&

.HYDROLOGY...
No widespread hydrologic impacts are expected through the
weekend. However, some brief heavy rain will be possible with
any thunderstorms.

Generally between 1-2 inches of average basin rainfall is expected
Mon into Tue, with the highest amounts N and W of NYC, however this
will depend on the exact track of a wave of low pressure riding
along a frontal boundary. At this time, think urban and small stream
flooding would be most likely, however if the axis of heaviest
rainfall shifts slightly SE, the threat for flash flooding will
increase.

&&

.CLIMATE...
The following are records for Sunday, July 21:

Record high minimum temperatures:

NYC:  82 in 1980
LGA:  83 in 1980
JFK:  79 in 2017
EWR:  81 in 1980
ISP:  76 in 1980
BDR:  76 in 1994

Record high temperatures:

NYC: 104 in 1977
LGA: 100 in 1991
JFK:  99 in 1991
EWR: 103 in 2011
ISP: 101 in 1991
BDR:  98 in 1991

&&

.EQUIPMENT...
NYC NOAA Weather Radio Station KWO35 (162.55 MHz) remains off
the air.

&&

.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Excessive Heat Warning until 8 PM EDT Sunday for CTZ005>012.
NY...Excessive Heat Warning until 8 PM EDT Sunday for NYZ067>075-
     078>081-176>179.
NJ...Excessive Heat Warning until 8 PM EDT Sunday for NJZ002-004-
     006-103>108.
MARINE...None.

&&

$$

SYNOPSIS...FEB/DW
NEAR TERM/SHORT TERM...DW
LONG TERM...24
AVIATION...Goodman
MARINE/HYDROLOGY...24/DW

NWS OKX Office Area Forecast Discussion