783
FXUS61 KPHI 150540
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
140 AM EDT Thu Aug 15 2024

.SYNOPSIS...
High pressure over the area moves offshore late Friday. A cold
front will slowly work its way across the region over the region
until departing on Monday. Meanwhile, Hurricane Ernesto will
remain well east of the coasts through the weekend. High
pressure builds in from the west starting on Tuesday.

&&

.NEAR TERM /THROUGH TODAY/...
Broad and weak surface high pressure will continue to influence
our region through Thursday as it migrates eastward. Tranquil
weather conditions will continue through the term.

Some upper-level shortwave energy is posed to pass through early
this morning. The isolated convection that developed earlier has
dissipated, and no additional convection is expected. A
tranquil night is on tap. Mostly clear skies with lows mainly in
the low to mid 60s (upper 50s at higher elevations) expected.
Light NNW winds and/or winds going light and variable for most
locations. Some very light patchy ground or valley fog may
occur.

For Thursday, high temperatures in mid 80s for most locations;
highs in the mid to upper 70s for the higher elevations and
coasts. Winds 5 kts or less, favoring a N to NW direction, or
remaining light and variable through much of the period. A sea-
breeze will likely develop, given the weak overall flow, and
could penetrate fairly inland by the evening. Some upper-level
shortwave energy could again pass through during the afternoon
and evening; a few isolated pop-up showers should not be ruled
during these time frames for areas, mainly north of the Philly
metro and along the sea breeze in interior southern New Jersey.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...
High pressure will be over the Northeast and will extend down
into the Mid-Atlantic Thursday night before lifting to the
northeast Friday night. With the high still influencing the
local area on Friday, this results in a slower approach of the
cold front.

Tranquil conditions Thursday night, and then clouds increase
throughout the day Friday. Temperatures will warm to several
degrees above normal with lows in the 60s Thursday night and
then highs in the mid to upper 80s with cooler temperatures at
the coasts and in the mountains on Friday. With the slower
approach of the cold front, showers really will not get going in
the western zones until after midnight Friday night, and even
then, PoPs are capped at chance.

Scattered showers and thunderstorms continue into Saturday, but
the activity really gets going by Saturday afternoon as
shortwave energy moves in from the west. Although temperatures
will be a few degrees shy of normal, dew points will rise into
the upper 60s and low 70s, so it will feel humid and muggy.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
What is currently Hurricane Ernesto will stay well east of the
Jersey Shore this weekend. However, large swells will impact the
coasts this weekend with elevated surf and dangerous rip
currents.

Low pressure over the Great Lakes will have a trough extending
down through the Ohio and Tennessee Valleys and into the Mid-
Atlantic. A cold front will extend down from this system and
will slowly work its way east over the weekend. Shortwave energy
exiting from the base of the trough will spin off a secondary
low near the Delmarva Peninsula Saturday night. With southerly
flow ahead of this system picking up moisture from the Atlantic
Ocean as well as Tropical Storm Ernesto which should be several
hundred miles east of Atlantic City, dew points will be up in
the low 70s, resulting in PWATs up around 2 inches. This will
result in periods of heavy rain Saturday night, which could lead
to localized flooding.

This secondary low departs by Sunday morning, and then there
may be a lull in the precip until Sunday afternoon. Low pressure
moves into central New York on Sunday, dragging the cold front
closer to the region. Another round of showers and thunderstorms
will develop Sunday afternoon and evening. Cold front then
works its way through the region Sunday night, and should be
cleared by Monday morning.

The trough, however, will lag behind the cold front, and a
secondary cold front will develop with this trough. Another
round of showers and thunderstorms will develop Monday afternoon
with the passage of this secondary front, but PoPs for now will
be capped mostly at chance with a small area of likely PoPs in
the southern Poconos. The trough, however, may get hung up over
the East Coast. While dew points will be coming down on Monday
behind the initial cold front, this secondary front will not
exactly moisture-starved with dew points in the 60s. By this
point, Ernesto will be long gone.

With that trough over the area, unsettled weather may continue
into Tuesday and maybe even Wednesday.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Early this morning...VFR/SKC. Winds 5 kts or less, favoring a N
to NW direction. Some sites (e.g., KMIV/KACY) will see winds go
light and variable for the period. High confidence.

Thursday...VFR. Winds 5 kts or less, favoring a N to NW
direction, or remaining light and variable through much of the
day. A sea- breeze will likely once again develop causing a
SE/SSE wind shift for at least KMIV/KACY. Sea-breeze my end up
penetrating further inland toward I-95 given the prevailing
background flow. High confidence overall, low confidence in sea-
breeze timing and distance.

Outlook...

Thursday night through Friday...VFR.

Friday night through Sunday night...Sub-VFR conditions from
time to time in SHRA, which may be heavy at times Saturday night
and Sunday night. Scattered TSRA as well.

Monday...Generally VFR. Scattered afternoon SHRA/TSRA possible
that may result in brief sub-VFR conditions.

&&

.MARINE...
No marine headlines are anticipated through Thursday. Winds
5-10 kts. Seas 1-2 feet. Fair weather.

Outlook...

Thursday night through Friday...Sub-SCA conditions.

Friday night through Sunday...SCA conditions expected, mainly
for elevated seas due to larger swells from Ernesto.

Monday...SCA conditions may continue as seas will be slow to
subside.

Rip Currents...

Thursday...Light north winds will become south 5 to 10 mph in
the afternoon as sea breezes develop. Breaking waves will be
around 1 foot with a 9 second period. Therefore, there is a LOW
risk for the development of dangerous and life threatening rip
currents at the Jersey Shore and at Delaware Beaches.

On Friday, south winds will increase to 10 to 15 mph with
occasional gusts up to 20 mph in the afternoon. Breaking waves
will average 2 to 3 feet. Given the flow will be parallel to the
Jersey Shore, there is a MODERATE risk for the development of
dangerous and life threatening rip currents for the Jersey Shore
and a LOW risk for the development of dangerous rip currents
for Delaware Beaches.

Over the weekend, Hurricane Ernesto will pass well east of the
mainland. Large swells from this storm will result in elevated
seas that should result in dangerous and life threatening rip
currents at the Jersey Shore and at Delaware Beaches for at
least Saturday and Sunday.

For specific beach forecasts, visit weather.gov/beach/phi

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...MPS
NEAR TERM...AKL/Staarmann/Wunderlin
SHORT TERM...MPS
LONG TERM...MPS
AVIATION...AKL/MPS/Staarmann/Wunderlin
MARINE...MPS/Wunderlin