000
FXUS61 KOKX 281532
AFDOKX
Area Forecast Discussion
National Weather Service New York NY
1132 AM EDT Fri Jul 28 2023
.SYNOPSIS...
High pressure over the Western Atlantic remains in control
through tonight. A cold frontal passage is expected Saturday
afternoon and evening. High pressure will then begin building
from Southern Canada on Sunday into Sunday night and remain in
control through the middle of next week. A frontal system could
impact the area late next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
Forecast remains on track early this morning. Only minor
adjustments to temperature and dew point to reflect the most
recent observations.
Changes to the heat headlines: Have cancelled the Excessive
Heat Warning for NE NJ and NYC metro and replaced with a heat
advisory. Otherwise, the heat advisory remains in effect for
Long Island, Southern Connecticut, Lower Hudson Valley, and
Western Passaic.
The justification for the cancellation of the Excessive Heat
Warning has been the consistent trend in recent days for heat
indices to peak 100-102 this afternoon. While it is not
entirely out of the question to see a few localized spots reach
a peak heat index around 105, do not think it will be
widespread enough to warrant the continuation of the warning.
The other factor is that the flow is a bit more westerly
compared to Thursday, which typically allows dew points to mix
out or lower in the afternoon. Rather than seeing dew points
persistently in the low to mid 70s, they will likely fall to the
upper 60s to around 70 in the afternoon. Some of the raw model
output indicates dew points could lower to the middle 60s in
some spots in NE NJ. Have not gone this aggressive yet, but is
something that could prevent the heat index from rising higher
than currently anticipated.
These factors do not change the overall message that it will
still be very hot and humid. The flow aloft is generally zonal
with the core of the ridging/anticyclone remaining across the
southern US. Heights may briefly rise into the afternoon as
well. The atmosphere aloft is much drier compared to Thursday.
Model soundings indicate a pretty strong cap between 6 and 8
kft. No convection is expected given these negating factors.
Actual air temperatures will quickly rise into the upper 80s
this morning then low to middle 90s in the afternoon. Some
upper 90s are possible across NE NJ. Max heat indices will
generally be 96 to 100 across the area, but 100-102 in NE NJ
and NYC metro.
Warm and very humid conditions continue tonight. Heights should
start to fall a bit in response to broad shortwave troughing
digging into the northeastern US from southeast Canada. Have
continued to forecast dry conditions for tonight, but there
could be some remnant convection from earlier activity to our
NW that may near the Lower Hudson Valley towards day break
Saturday. Lows in the NYC metro and urban NE NJ may struggle to
fall below 77-80 degrees with the rest of the area generally in
the low to middle 70s.
&&
.SHORT TERM /SATURDAY THROUGH SUNDAY/...
Heat Advisory remains in effect for the entire area on Saturday.
The risk for severe thunderstorms has increased a bit with SPC
now including much of the region in a slight risk.
A relatively strong cold front will move across the area in the
afternoon and evening. There may be some initial shortwave energy
that moves across in the morning. Given that instability will be on
the increase, cannot rule out some elevated convection in the
morning. The chances for convection appear higher in the
afternoon and evening with the cold front passage. Several CAMs
are hinting at a frontal wave on the front as it moves into the
area. This could enhance the coverage of convection and
potentially the severe weather threat. Confidence in the
location of this wave is very low at this time. The CAMs have
also been inconsistent with many of the recent events with
regards to placement/timing of specific mesoscale features and
the resulting convection. Model soundings, specifically the GFS,
indicate a middle level cap holding on until the cold front
passage in the late afternoon and evening. The NAM/NAMnest
indicates a cap in the morning, but it weakens quickly in the
afternoon with a line of convection moving with the front late
in the day. There is enough evidence to support raising PoPs to
likely in the afternoon and evening from N to S give falling
heights and convergence along the front. Forecast confidence is
still relatively low on coverage of severe weather, but the
atmosphere appears to become quite unstable with CAPES close to
2500 J/kg. 0-6 km bulk shear values may also range from 35 to 40
kt. The overall convective evolution should continue to become
clearer over the next 24 hours.
The main severe threat is from damaging wind gusts. A localized
brief tornado cannot be ruled out as there is some directional
low level shear on the latest soundings. Locally heavy rainfall
is possible in any thunderstorm leading to potential of
localized flash flooding.
There has not been much change to the thinking with regards to the
heat and humidity for Saturday. Highs should top out a few degrees
lower than Friday in the upper 80s and low 90s outside of the NYC
metro and urban NE NJ where highs in the low to mid 90s are
forecast. Dew points look a bit higher compared to Friday, so max
heat indices overall are similar, generally 95-102, highest in
the NYC metro and NE NJ.
The cold front sinks south of the area Saturday evening and
Saturday night. Any convection should push offshore with the
front. Cooler and drier air will begin to advect in behind the
front.
Much cooler and lower humidity levels are expected on Sunday.
The upper level pattern shifts back to one that has been more
persistent for much of the summer, with upper level troughing
over the NE US and upper level ridging over the western and
central US. High pressure will begin building in from southern
Canada on Sunday. Heights will continue falling aloft as the
upper trough settles overhead. The GFS has been most aggressive
with an amplified piece of energy within the flow moving through
Sunday afternoon. Other models are less aggressive, but have
kept PoPs at slight chance for a shower in the afternoon.
Otherwise, highs will be a few degrees below normal for this
time of year in the lower to middle 80s.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Next week is setting up to feature the most comfortable airmass
we have seen in several weeks. High pressure starts to build in
Sunday night, dropping down from Southern Canada. It looks to
become centered over the area on Wednesday before shifting
offshore. Aloft, an upper level ridge sets up over the east
coast, with multiple embedded shortwaves swinging through and
assisting in reinforcing shots of cooler, drier air.
This will be an anomalously dry airmass for this time of the
year. Dewpoints on Wednesday will be in the upper 50s. The 7/28
00z run of the GFS has pwat values of 0.5 inches to 0.6 inches
across the area at 12z on Wednesday. The current lowest recorded
pwat value of the OKX sounding on 8/2 per SPCs Sounding
Climatology Page is 0.56.
High temperatures each day will be in the upper 70s to mid 80s.
These temperatures are about 5 degrees cooler than normal for
late July/early August. Stuck mostly with the NBM for
temperatures, except Tuesday night. With the global models in
decent agreement of the location of the high being nearly
centered overhead, thinking there will be good radiational
cooling conditions that the NBM was not capturing. Blended in
some of the MEX guidance to get low 50s across the interior and
LI Pine Barrens.
Dry conditions and mostly sunny skies are expected through
Wednesday. Wednesday night, an upper level low and associated
surface low approach, moving through eastern Canada. The system
could impact the area as early as Thursday, but looks to drag a
cold front through later. There are still timing, strength and
location differences this far out in the guidance as expected.
Had enough confidence to keep the NBM low end chance PoPs
starting Thursday afternoon.
&&
.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
A surface trough remains near or over the area, with high
pressure anchored over the western Atlantic.
VFR. Light NW flow becoming W/SW at 7-12kt by this afternoon.
Seabreeze development will be likely by mid to late aftn. Flow
stays out of the W/SW through Friday night, but weakens to
around 5 kt.
...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty...
Timing of multiple wind shifts today may vary by 1-2 hours.
OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY...
Saturday: Mainly VFR. Chance of mainly afternoon and evening showers
and thunderstorms with MVFR possible.
Sunday: Mainly VFR. Slight chance of an afternoon shower.
Monday-Tuesday: VFR.
Detailed information. including hourly TAF wind component forecasts,
can be found at: https:/www.weather.gov/zny/n90-- End Changed Discussion --
&&
.MARINE...
A Marine Weather Statement continues for Long Island Sound. The
US Coast Guard still indicates a large debris field caused by
recent flooding across New England.
sub-SCA conditions are now expected on all waters through
tonight. S-SW winds increase on Saturday ahead of the next cold
front. There may be some gusts close to 20 kt, but winds likely
stay below 25 kt. However, seas build to 5 ft Saturday afternoon
into Saturday night, especially east of Fire Island Inlet.
Otherwise, sub-SCA conditions are expected Sunday through the
middle of the week with high pressure building over the waters.
There is potential for a frontal system to impact the area late
in the week and it could bring building seas to 5 ft or greater
in a strengthening SW/S flow.
&&
.HYDROLOGY...
Locally heavy rain which could lead to localized flash flooding
is be possible with the cold frontal passage on Saturday
afternoon and evening.
No hydrologic concerns are expected Sunday through next week.
&&
.TIDES/COASTAL FLOODING...
There is a moderate rip current risk today. On Saturday, with and
increasing SW flow and building waves, there is a high rip current
risk.
&&
.CLIMATE...
Today`s (July 28) Record High Temperatures
Central Park...97 (1892, 1931, 1949, 1999)
LaGuardia......98 (1949)
JFK............98 (1949)
Newark........101 (1949)
Islip..........96 (1999)
Bridgeport.....95 (1949)
Today`s (July 28) Record High Minimum Temperatures
Central Park...80 (2020)
LaGuardia......83 (2020)
JFK............79 (2020)
Newark.........80 (2020)
Islip..........77 (2020)
Bridgeport.....77 (2020)
&&
.OKX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Saturday for CTZ005>012.
NY...Heat Advisory until 8 PM EDT Saturday for NYZ067>075-078>081-
176>179.
NJ...Heat Advisory until 8 PM EDT Saturday for NJZ002-004-006-
103>108.
MARINE...None.
&&
$$
SYNOPSIS...DS/JT
NEAR TERM...DS/MW
SHORT TERM...DS
LONG TERM...JT
AVIATION...JMC/JT
MARINE...DS/JT
HYDROLOGY...DS/JT
TIDES/COASTAL FLOODING...
CLIMATE...