831
FXUS61 KPHI 150758
AFDPHI

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

.SYNOPSIS...
Weak high pressure over the area moves offshore late Friday, then a
cold front slowly works its way across our region Sunday night
before moving offshore on Monday. Meanwhile, Hurricane Ernesto will
track well east of our region during the weekend. High pressure
builds in from the west later Tuesday through Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Broad high pressure will continue to be the dominant feature through
the near term forecast period but it will be weakening and slowly
drifting eastward through this timeframe.

Temperatures early this morning are in the upper 50s to mid 60s
across the area with a few spots in the heart of the urban corridor
remaining near 70. Skies are clear with light winds which is
resulting in some valley fog/patchy ground fog, particularly in
northwest New Jersey. The valley fog may extend southward into the
Lehigh Valley as we head towards dawn this morning.

For the daytime hours today, temperatures will be in the mid 80s
across most of the area (some upper 70s at the coast and higher
elevations). With the center of the high slowly drifting to the
east, winds look to be even lighter today compared to yesterday
(less than 10 mph for most locations). A sea breeze looks to again
develop this afternoon, and with the light flow, may make it into
the I-95 corridor by this evening. Skies look to be partly to mostly
sunny as some cumulus develops in the afternoon hours. Some mid and
upper-level shortwave energy may once again help spark a few
isolated showers or a thunderstorm this afternoon/evening, most
likely in northern New Jersey as well as along the sea breeze in
southern New Jersey.

With cumulus and any convection once again rapidly dissipating after
sunset, conditions tonight will be quite similar to early this
morning. Surface high pressure becoming centered near/south of the
region will lead to mostly clear skies and light to calm winds. Lows
mainly in the 60s expected.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
Turning more humid to start the weekend and also an increase in the
chances for showers and thunderstorms. Dangerous rip currents and
surf are expected due to distant Hurricane Ernesto.

A closed low centered over the Midwest and Upper Great Lakes Friday
will slowly shift eastward through Saturday night. Some weak ridging
in the mid levels Friday is forecast to slide across our area, which
will support a weak area of high pressure. This along with a slower
eastward advancement of the closed low results in a dry Friday, at
least during the daytime hours. While some clouds are expected to
increase, a slower arrival of the aforementioned trough should
result in more sunshine hanging on longer Friday. The low-level flow
turns more southerly Friday and this will start to advect more low-
level moisture into our area, however a warm front is forecast to
still be to our west and southwest. As a result, a very warm Friday
afternoon is forecast with many areas getting into the upper 80s
(some spots could touch 90 degrees). Ample boundary layer heating
may lower the dew points some during peak heating, then these start
to inch up through the 60s at night. Showers and thunderstorms well
to our west during the day Friday are forecast to arrive into at
least our western zones during the evening and spread eastward
overnight. This is also within a moisture plume as precipitable
water values increase to 1.5-2.0 inches. Some of this activity
however may dissipate with an eastward extent given lowering
instability and it outrunning the main forcing for ascent.

As we go through Saturday, a humid air mass is forecast to
overspread our area as a warm front arrives and boosts the dew point
to 70 degrees or above. An initial band of convection looks to push
across our western and northern areas with this possibly extending
father south. The precipitable water values are forecast to be
around 2 inches, and this will set the stage for locally heavy
rain (possibly localized flash flooding) associated with the
convection. There may be multiple rounds of showers and some
thunderstorms (some possibly organized into clusters), with an
increase especially later in the afternoon and evening as
height falls overspread our area with the incoming upper-level
trough. The intensity of the thunderstorms will depend on the
extent of the cloud cover (instability), and the shear magnitude
which looks to be on the weak side in our area. Weaker mid level
lapse rates may also hold down the instability some. Overall
though as of now, an isolated risk for severe thunderstorms
is mainly to our west and southwest.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Summary...Some showers and thunderstorms continue into early next
week as a cold front works its way across our area and then
offshore. Hurricane Ernesto remains well offshore into Monday,
although dangerous surf and rip currents will continue for a while
longer.

Synoptic Overview...An upper-level trough shifts eastward and
settles across the Northeast and Mid-Atlantic regions. This trough
may be reinforced around mid-week. At the surface, low pressure
tracks to our north Sunday into Monday and a cold front then crosses
our area Sunday night into Monday. A weak surface low may develop
across our area Sunday night into Monday along the occluded
front/triple point. A secondary cold front may move through during
Tuesday, then high pressure gradually arrives later Tuesday through
Wednesday.

For Sunday and Monday...Surface low pressure tracks to our north
with a trailing cold front working its way across our area Sunday
night into Monday. As the trough axis gets much closer, a secondary
low may develop along the occluding front/triple point as it crosses
our area. A humid air mass (dew points into the lower 70s) will
remain in place ahead of the cold front and this keeps the
precipitable water values at around 2 inches. Forcing for ascent
with the incoming trough and front/low will result in showers and
some thunderstorms especially each afternoon and evening. A locally
heavy rain risk is present, although the flash flooding potential at
this time looks to be on the low side. The intensity of
thunderstorms is less certain as this will depend on the extent of
the showers, cloud cover and magnitude of the instability. The PoPs
increase with these peaking mostly each afternoon and evening. This
trough will keep Hurricane Ernesto and its associated moisture
maximum well east of our area.

For Tuesday and Wednesday...The upper-level trough is forecast to
remain over the East, with it possibly being reinforced some into
Wednesday. While the initial cold front is well offshore, a
secondary cold front may move through from the northwest sometime
during Tuesday. Meanwhile, surface high pressure centered near the
Midwest tied to a ridge should build toward our area. While a shower
or thunderstorm cannot be ruled out with the presence of the trough
aloft and the incoming secondary cold front, the chances look
reduced given additional drying and surface high pressure building
more into our area. Dew points are forecast to lower and the
temperatures also cool.

&&

.AVIATION /08Z 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.

Today...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 beginning around 18-20Z. Sea-breeze
my end up penetrating further inland toward I-95 given the
prevailing background flow. High confidence overall, moderate
confidence in sea- breeze timing.

Tonight...VFR with mostly clear skies. Winds light and variable
to calm at times. High confidence.

Outlook...

Friday through Sunday...Times of sub-VFR conditions due to showers
and some thunderstorms some of which could be locally heavy,
starting Friday night into Saturday.

Monday..Some additional showers and thunderstorms around.

&&

.MARINE...
No marine headlines are anticipated through tonight. Winds around 5-
10 kts with seas around 1-2 feet. Fair weather.

Outlook...

Friday...The conditions are anticipated to be below Small Craft
Advisory criteria.

Saturday and Sunday...Small Craft Advisory conditions especially for
the Atlantic coastal waters, mainly for elevated seas due to larger
swells from distant Hurricane Ernesto.

Monday...The Small Craft Advisory conditions may continue as
seas/swells slowly subside.

Rip Currents...

Today...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 rip currents at the Jersey Shore and
at Delaware Beaches.

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 with a long period swell of 12-14 seconds developing.
Given the increasing period, wave height, and winds, there is a
MODERATE risk for the development of dangerous rip currents for
the Jersey Shore. With winds more parallel/slightly offshore,
there is a LOW risk for the development of dangerous rip
currents for Delaware Beaches.

For Saturday and Sunday, Hurricane Ernesto will track well east
of our region. However, larger swells arriving from this storm
and breaking into the surf zone will result in very dangerous
rip currents at the Jersey Shore and at the Delaware Beaches.

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

&&

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

&&

$$

SYNOPSIS...Gorse
NEAR TERM...AKL
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...AKL/Gorse
MARINE...AKL/Gorse