Forecast Discussion

527
FXUS61 KPHI 061101
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
701 AM EDT Thu Aug 6 2026

.WHAT HAS CHANGED...
The Heat Advisory was extended through Saturday for the I-95
corridor and portions of central and southern New Jersey, and
now includes coastal Monmouth County.

The end time of the Heat Advisory for Carbon and Monroe
Counties was changed to end at 8 PM this evening.

&&

.KEY MESSAGES...
1. Hot and very humid conditions are expected to persist
through Tuesday of next week. A Heat Advisory is in effect for
portions of the area.

2. There are daily chances for showers and thunderstorms through
Saturday, as well as much of next week. There is at least a
marginal risk each day for localized heavy rainfall leading to
flash flooding and locally damaging wind gusts with any stronger
thunderstorms that develop.

&&

.DISCUSSION...
KEY MESSAGE 1...Hot and very humid conditions are expected to
persist through Tuesday of next week. A Heat Advisory is in
effect for portions of the area.

A relatively stagnant synoptic pattern is developing across our
region. Quasi zonal mid and upper level flow will be in place
through the middle of next week as Bermuda high pressure
persists offshore. This will keep a steady stream of very warm
and moist air in place across the region through the period.

A prolonged period of hot and, most notably, very humid
conditions is expected to remain in place for the next several
days. We look to have a weak cold frontal passage early Sunday,
ushering in slightly drier air. This will give some slight
reprieve from the excessive humidity, though highs will still
be in the upper 80s to low 90s. Moisture advection will return
again by Monday though, and hot and very humid conditions are
anticipated to return Monday through Tuesday. A somewhat
stronger cold front looks to come through late Tuesday or
Wednesday, which will help break the excessive heat and humidity
some.

A Heat Advisory remains in effect for portions of eastern
Pennsylvania, much of New Jersey except the far southern
counties, as well as New Castle, Delware. The Heat Advisory was
expanded to include coastal Monmouth County, as southwesterly
surface winds should prevent the sea breeze from making much
inland progress there. The end time of the Heat Advisory for
Carbon and Monroe Counties was changed to end at 8 PM this
evening, as the forecast for Friday has trended well below
advisory criteria. The Heat Advisory for the I-95 corridor and
portions of central and southern New Jersey was extended through
8 PM Saturday, where confidence is highest in heat indices
reaching near or over 100 degrees on Saturday. Elsewhere in
eastern Pennsylvania and northern New Jersey, the Heat Advisory
remains in effect through 8 PM Friday.


KEY MESSAGE 2...There are daily chances for showers and
thunderstorms through Saturday, as well as much of next week.
There is at least a marginal risk each day for localized heavy
rainfall leading to flash flooding and locally damaging wind
gusts with any stronger thunderstorms that develop.

A relatively stagnant synoptic pattern is developing across our
region. Quasi zonal mid and upper level flow will be in place
through the middle of next week as Bermuda high pressure
persists offshore. This will keep a steady stream of very warm
and moist air in place across the region through the period,
with varying kinematics and forcing aloft. Mid level flow does
appear to increase by early next week, which may be more
supportive of better organized and stronger convection compared
to this week.

Diurnally driven instability will be in the 1000-2000 J/kg each
afternoon through the next several days along with PWats in the
1.5-2" range. Mean flow will be predominantly southwesterly and
relatively weak through Saturday. This will support a continued
localized heavy rainfall threat with potential for flash
flooding, although water loaded downdrafts could cause localized
wind damage. Areas with very saturated ground from recent rains
will be most prone to experiencing trees falling.

Convection today should be confined primarily northwest of the
I-95 corridor where forcing aloft is most supportive, though
cannot rule our some storms making it as far southeast as the
I-95 corridor. SPC and WPC maintain a Marginal Risks in this
area. On Friday, convection looks to be greater in coverage, and
perhaps more organized given the forcing and shear profiles. So
we could see a somewhat greater damaging wind threat if any
organized linear structures materialize. However, low level
lapse rates will be poor and there`s a notable lack of mid level
dry air to strengthen downdrafts. Overall, looking at marginal
risks of flash flooding and damaging wind gusts with greater
coverage and organization of storms anticipated on Friday.

Details for Saturday`s convection remain unclear, but we could
certainly end up with some potential for flash flooding and severe
storms again. Current indications in the guidance support a
later timing of storms during the evening or even overnight
depending on the timing of a weak cold front and shortwave
trough.

We look to have a weak cold frontal passage by early Sunday,
ushering in slightly drier air. This combined with subtle
subsidence aloft will help briefly limit convection potential on
Sunday and also give some slight reprieve from the excessive
humidity, though highs will still be in the upper 80s to low 90s.
Moisture and forcing aloft will return by Monday as mean flow
shifts more westerly and mid level flow increases. This should
result in a greater severe thunderstorm threat compared to this
week, and perhaps slightly lower flash flooding threat, but the
details into the period early next week remain unclear. Long
story short, Monday and Tuesday look to continue the hot and
humid conditions and daily thunderstorm chances.

A somewhat stronger cold front looks to come through late
Tuesday or Wednesday, which will help break the excessive heat
and humidity some, but the pattern aloft may still support
diurnally driven convection.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Today...Any restrictions around 12Z will quickly improve to VFR
by 13-14Z. Afternoon SHRA/TSRA may impact KRDG/KABE, then
KTTN/KPNE/KPHL/KILG. Have opted to include PROB30 groups for
TSRA at the I-95 terminals, where the probability of direct
impact form this activity is lower. Southwest winds 5-10 kts,
becoming gusty at ACY/MIV by 18Z. High confidence in prevailing
VFR conditions much of the day, but low confidence on SHRA/TSRA.

Tonight...Any SHRA/TSRA taper off in the evening. Generally
VFR, though patchy fog possible. South winds 5 kts or less.
Moderate confidence overall, low confidence on any fog
developing.

Outlook...

Friday through Monday...Restrictions possible in afternoon and
evening SHRA/TSRA each day, though Sunday looks dry, and patchy
fog possible at night.

&&

.MARINE...
No marine hazards expected through tonight. Southerly winds
increasing to 15-20 kts by this afternoon, diminishing some
overnight. Seas 2-4 feet.

Outlook...

Friday through Monday...No prevailing marine hazards are
forecast. However, there could be some afternoon and evening
showers and thunderstorms Friday, Saturday, and Monday, which
could locally increase winds and seas. South to southwest winds
10-20 kts and seas 2-4 feet, greatest in the afternoon and
evening periods.

Rip Currents...

For today, south to southwest winds will increase to 15 to 20
mph in the afternoon with breaking waves in the surf zone of 1
to 3 feet. There will be a light easterly swell with a period
around 10 seconds. Opted to go with a MODERATE risk for the
development of dangerous and life threatening rip currents for
Cape May and Atlantic Counties, where the wind will have a
greater onshore component, and a LOW risk elsewhere for the
Jersey Shore and for Delaware Beaches.

Conditions will be fairly similar on Friday, thus maintained the
same risk levels as today.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
PAZ070-071-102-104-106.
Heat Advisory from 10 AM this morning to 8 PM EDT Friday for
PAZ060>062-101-103-105.
Heat Advisory from 10 AM this morning to 8 PM EDT this evening
for PAZ054-055.
NJ...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
NJZ010-012>015-017>020-027.
Heat Advisory from 10 AM this morning to 8 PM EDT Friday for
NJZ001-007>009.
DE...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for
DEZ001.
MD...None.
MARINE...None.

&&

$$

DISCUSSION...Robertson/Staarmann
AVIATION...Staarmann
MARINE...MPS/Staarmann

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Data at: 0000 UTC 03 Sep 2023

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