030
FXUS61 KPHI 160804
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
404 AM EDT Fri Aug 16 2024

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

&&

.NEAR TERM /THROUGH TONIGHT/...
Broad high pressure moving offshore will bring us a dry end to the
work week before the next low pressure system begins to approach the
region tonight.

Temperatures early this morning are in the mid 60s across much the
area with a few spots in the heart of the urban corridor remaining
above 70 and higher elevations dipping below 60. Skies are again
mostly clear with light to calm winds. Temperatures are forecast to
fall into the low 60s across most of the region though the urban
corridor is expected to remain in the upper 60s. We are again seeing
indications this morning of the formation of some valley fog/patchy
ground fog, but again, this should burn off relatively quickly after
sunrise.

For the daytime hours today, temperatures will be in the upper 80s
to near 90 across most of the area (a few upper 70s remaining
sprinkled in at the coast and higher elevations) as southerly flow
returns to the region with the high sliding offshore. While the
center of the surface high is drifting away, the arrival of the
upper level ridge will increase subsidence and should keep the
entire area dry through the day today. The ridge then passes
offshore later this evening into tonight.

With the departure of the upper-level ridge and surface high, the
next low pressure system will then begin to approach our region
tonight. Guidance maintains a slightly slower progression so most of
the area should stay dry tonight and any areas that do see some
widely scattered showers, likely won`t see them until well after
midnight tonight. PoPs 20-40% for the western third of the region
(increasing from east to west) with lower PoPs everywhere else. With
increasing clouds and continued light southerly winds, lows look to
be in the upper 60s to near 70 across most of the region.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
Showers and some thunderstorms increase during the weekend as a slow
moving system arrives from the west.

As low pressure moves into the eastern Great Lakes on Saturday,
another shortwave will slide out ahead of it, resulting in showers
and some thunderstorms increasing by later Saturday afternoon and
night. Southerly will result in a humid air mass as dew points
increase into the upper 60s to low 70s Saturday then into the lower
to perhaps mid 70s on Sunday. Given the precipitable water values of
around 2 inches, locally heavy rain will occur with any heavier
convective cells especially along and north/west of I-95. The
coastal areas may remain dry during much of Saturday. While some
convective may attempt to organize into a few small clusters across
mainly parts of our western zones, the severe weather risk looks to
mainly be to our west and southwest where there is a Marginal Risk
(level 1 out of 5).

As we go through Sunday, additional showers and thunderstorms are
expected especially in the afternoon and evening as increasing
forcing for ascent overspreads the region and a cold front starts to
arrive. The available moisture, with precipitable water values
around 2 inches, will once again lead to potentially locally heavy
rain. As the front gradually works its way across our area later
Sunday, a secondary low develops along it in the vicinity of our
area. This may assist in focusing a cluster of showers/thunder with
locally very heavy rain. As a result, the flash flooding risk has
increased some for Sunday afternoon and evening from about the urban
I-95 corridor to the north and west (Slight Risk, level 1 out of 4,
for excessive rainfall leading to flash flooding for parts of our
area). While the deep-layer shear is forecast to be on the weaker
side, enough instability along with steepening low-level lapse
rates may result in an isolated severe thunderstorm risk
(Marginal Risk, level 1 out of 5) with locally strong winds the
main threat, especially if some convective cores become strong
enough to promote more efficient downdraft winds due to water
loading.

While PoPs for measurable rainfall are included in the region for
the entire weekend, it is not expected to be a washout and the
greatest showers and some thunderstorms should be mostly each
afternoon and evening. In addition, Hurricane Ernesto will track
northward with its center remaining several hundred miles east of
our area, and this will keep the associated moisture maximum also
out to sea. Therefore while there will be no direct impacts to our
area from the hurricane, larger swells will be driven into the coast
resulting in rough surf conditions and there will also be
dangerous/life-threatening rip currents.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Summary...Some showers and thunderstorms Monday, then improving
conditions along with it becoming noticeably cooler and less humid.

Synoptic Overview...An upper-level trough remains across the East
however this is forecast to weaken some with time. At the surface, a
cold front is forecast to be shifting offshore Monday, then a
secondary cold front arrives during Tuesday. An area of high
pressure builds eastward later Tuesday and settles over our area
Wednesday into Thursday.

For Monday...An upper-level trough will continue to overspread the
East, and this will drive a cold front offshore of our area. While a
humid air mass will continue, some lowering of the high dew points
is expected to occur late in the day and especially at night.
Forcing for ascent with the arriving trough and slowly exiting front
will result in some additional showers and thunderstorms especially
in the afternoon and early evening. Plenty of moisture in place will
once again provide the potential for some locally heavy rain.

For Tuesday through Thursday...The upper-level trough is forecast to
remain over the East, although it may weaken some with time. Some
guidance has indicated the trough becomes reinforced Tuesday,
however some of that same guidance has now shifted this more up into
New England. A secondary cold front may move through from the
northwest Tuesday, and while this looks to be weak at this time kept
in slight chance PoPs (20 percent) for possible isolated showers.
Meanwhile, surface high pressure centered near the Midwest tied to a
ridge builds toward our area later Tuesday, then it should settle
over our area Wednesday into Thursday. A noticeably cooler and less
humid air mass is forecast to continue to advect into our area, with
most of the area topping out into the 70s both Tuesday and Wednesday
and then perhaps a touch warmer on Thursday.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Early this morning...VFR with some passing clouds. Winds light and
variable to calm at times. High confidence.

Today...VFR with some scattered cumulus clouds and building cirrus.
Winds light in the morning becoming S-SSW around 5-10 kts in the
afternoon. Sea breeze at KMIV/KACY after 18-20Z may lead to a subtle
wind shift to the SSE. High confidence on prevailing VFR conditions.

Tonight...VFR conditions expected with increasing mid-level clouds,
particularly after 06Z. An isolated shower may approach KRDG/KABE
after 09Z. SSE winds around 5 knots or less. High confidence on
prevailing VFR conditions.

Outlook...

Saturday and Sunday...Times of sub-VFR due to showers and some
thunderstorms, some with locally heavy rain, especially each
afternoon and evening. Some areas of stratus possible.

Monday...Times of sub-VFR with some showers and thunderstorms,
especially in the afternoon and evening.

Tuesday...VFR.

&&

.MARINE...
No marine headlines are anticipated through the day today. For
tonight, a Small Craft Advisory remains in effect for Atlantic Ocean
coastal waters beginning at 10 PM EDT. Seas initially 1-2 feet this
morning building to 2-4 feet later this afternoon. Seas begin to
exceed 5 feet late this evening and continue to build towards 5-7
feet by late tonight. Winds of 5-10 kts with gusts around 15 knots
expected throughout the period.

Outlook...

Saturday and Sunday...A Small Craft Advisory now in effect through
Sunday night for the New Jersey and Delaware Atlantic coastal waters
for seas 5 to 7 feet due to larger swells from distant Hurricane
Ernesto. The conditions on Delaware Bay are anticipated to stay
below Small Craft Advisory criteria.

Monday...Small Craft Advisory conditions linger as seas slowly
subside on the Atlantic coastal waters. The conditions on Delaware
Bay are anticipated to stay below Small Craft Advisory criteria.

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

Rip Currents...

Today...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 and 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.
Breaking waves could reach as high as 5 to 8 feet. Some beach
erosion is possible. The high risk of rip currents could linger into
early next week as well.

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

&&

.TIDES/COASTAL FLOODING...
With long period swells and rough seas/surf expected to arrive this
weekend from distant Hurricane Ernesto coinciding with an
approaching full moon on Monday, at least some spotty minor coastal
flooding is anticipated to develop along the Atlantic coasts of New
Jersey and Delaware, Delaware Bay, and the tidal Delaware River. The
primary high tide cycles of impact will be evening to nighttime high
tides, perhaps beginning as early as Saturday in some areas. As long
period swells persist and astronomical high tides increase Sunday
and Monday, more widespread minor coastal flooding may be possible
with the evening to nighttime high tides those days.

Anyone with interests in these areas that are susceptible to minor
coastal flooding should monitor the latest forecasts and remain
alert for any advisories that may be issued in future updates as
confidence in the forecast increases.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...High Risk for Rip Currents from late tonight through Sunday evening
     for NJZ014-024>026.
DE...High Risk for Rip Currents from late tonight through Sunday evening
     for DEZ004.
MD...None.
MARINE...Small Craft Advisory from 10 PM this evening to 6 AM EDT
     Monday for ANZ450>455.

&&

$$

SYNOPSIS...Gorse
NEAR TERM...AKL
SHORT TERM...Gorse
LONG TERM...Gorse
AVIATION...AKL/Gorse
MARINE...AKL/Gorse/Staarmann
TIDES/COASTAL FLOODING...Staarmann