252
FXUS61 KPHI 160845
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
445 AM EDT Mon Sep 16 2024

.SYNOPSIS...
High pressure will be in control through tonight. An area of
low pressure tracks northwestward into and across the Carolinas
through the middle of this week, bringing increasing chances for
showers across our area. Unsettled conditions persist through
the end of the week, though high pressure tries to build in for
next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
Temperatures this morning have cooled rather quickly in well-
sheltered areas despite some cloud coverage. Some areas will begin
the morning with a rather cool start with temperatures dipping into
the low 40s for some. Patchy shallow fog cannot be ruled out at some
locations.

High pressure remains in place across coastal New England, but is
expected to begin to weaken as a tropical low off the coast of the
Carolinas inches north and west. Modest onshore flow between the two
systems will remain in place with NE winds this morning becoming
more ENE to E this afternoon with some gusts 20 to 25 mph,
especially closer to the coast. This along with increasing cloud
coverage will likely hinder temperatures from warming much this
afternoon, thus forecasted highs are only expected in the upper 70s
with some low 70s across the Pocono Plateau. That said, dew points
will be creeping back up, returning to the low to mid 60s across the
coastal plains south and east of the I-95 corridor.

Cloud coverage Monday night will help keep temperatures rather mild
with lows only cooling down to the upper 50s and mid 60s. Some high
res guidance suggest an isolated shower or two may be possible
closer to daybreak Tuesday as our tropical low off the Carolinas
crawls further north and west and the very fringes of its outer rain
bands may reach the Delmarva or the southern Jersey Shore. Impacts
remain minimum for this early morning timeframe.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Potential Tropical Cyclone 8 continues to meander off the coast of
the Carolinas and will move northwestward today. The storm will make
landfall this evening and move into central NC and western Virginia.
The associated tropical moisture will be advected northward into our
region, bringing the potential for some tropical downpours, with
forcing supplied by several shortwaves moving around the eastern
side of an upper level low setting up over the Piedmont/Blue Ridge
Mountains.

The first and perhaps strongest wave comes through late Tuesday.
Guidance has trended later with rain and embedded thunderstorms
overspreading the region, and Tuesday now looks mainly dry with the
exception of southern zones within the Delmarva peninsula. Thinking
the heaviest rain will now come more late Tuesday Night into
Wednesday morning. With PWATs pushing 2 inches, some heavy downpours
are possible. However, total rainfall amounts have come down, though
the spread among guidance remains large, indicating a low-confidence
forecast. The 25th and 75th percentile of total rainfall amounts
from the NBM ranges between a half inch (25th percentile) and two
inches (75th percentile) from Philadelphia on south. However, the
message remains the same overall. Some heavy rain is possible,
though really not expecting widespread flooding issues given how dry
it has been as of late, and where the heaviest axis of rainfall
looks to set up (over the sandy and absorbent soils of Delmarva and
southern New Jersey). A MARGINAL risk for excessive rainfall is
in place for the middle of the week, which is about right given
the factors mentioned above. The forecast right now has around
half an inch to an inch from Philadelphia on south, with locally
higher amounts possible. Rainfall amounts gradually diminish
the further north you go from the Philadelphia metro area.

Temperatures look to be in the 70s both Tuesday and Wednesday, with
mild overnight lows expected given the tropical airmass. Lows both
Tuesday and Wednesday Night will be in the 60s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
A relatively stagnant pattern will likely exist for the back half of
the week, with a closed upper low level low somewhere in the
vicinity. This closed low will eventually transition to an open
trough and slowly push over the region and then offshore. This will
result in unsettled conditions through Thursday Night, with rain
chances around 20-40% through that period, with perhaps a rumble of
thunder mixed in there. Not overly impactful rain overall-beneficial
if anything.

Most of the deterministic and some of the ensembles want to try to
have a ridge building in over a trough off to the south/southeast
for the end of the week and into the weekend. The placement of these
features will have large implications for the weekend weather. A
stronger ridge, which would have more influence over the region,
shunting the trough and area of low pressure to the south and
east. This would result in drier weather while a weaker ridge
would result in the trough staying nearby, bringing some showers
and unsettled weather. Would lean toward the drier solution at
the moment, though some showers would remain possible over far
South Jersey and Delmarva Friday into Sunday.

Given the abundance of moisture and onshore flow setting up through
the end of the week, expect muggy days and lots of cloud cover. This
will suppress daytime highs to be near/just below normal with mild
overnight lows and less of a diurnal range of temperatures. The
weekend looks like it could a bring a drier and more early autumn-
like airmass with low 70s for highs and 50s for lows.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Rest of tonight (through 12Z)...VFR, however some low clouds will be
near KACY and KMIV especially by daybreak and some localized fog
cannot be ruled out. East-northeast winds around 5 knots becoming
locally light and variable to calm. Low confidence on stratus
development and timing as well as any fog.

Monday...Some low clouds possible in the morning, otherwise VFR with
some cumulus and also high level clouds. East-northeast winds
increasing to 8-15 knots through the morning. Some gusts to 20-25
knots, mainly at KACY. Low confidence regarding low clouds in the
morning.

Monday night...Low clouds begin to develop with MVFR/IFR CIGs. Winds
E becoming NE around 5-10 kts. Moderate confidence.

Outlook...

Tuesday through Tuesday Night...MVFR/IFR conditions possible
especially from KPHL on south with low clouds and rain arriving
later in the day, continuing into the overnight hours.

Wednesday through Wednesday Night...Periods of MVFR/IFR likely with
scattered showers and isolated thunderstorms. Low clouds hang around
in between periods of rain.

Thursday through Friday...Sub-VFR conditions possible (40-60%) with
scattered showers and isolated thunderstorms. Low clouds likely to
be around in between periods of rain.

&&

.MARINE...
Added Small Craft Advisories for northern coastal waters off
Monmouth County NJ beginning Monday morning and the lower Delaware
Bay beginning Monday afternoon. Now all coastal waters and the lower
Delaware Bay will be under a SCA. Seas will continue to build to 4-7
feet through today and tonight. ENE winds will gust to 25 kts for
the southern coastal waters and lower Delaware Bay.

Outlook...

Tuesday through Tuesday Night...Small Craft Advisory in effect
for the ocean zones through Tuesday Night as seas of 5 to 6 feet
are expected with periods of 25 kt gusts. Small Craft Advisory
in effect for the lower Delaware Bay through Tuesday as gusts
hover around 25 kt. No marine headlines expected for the upper
Delaware Bay at this time.

Wednesday through Wednesday Night....SCA conditions possible (50-
60%) as seas hover around 4 to 5 feet. An extension may be needed to
the existing Small Craft Advisory.

Thursday...Small Craft Advisory conditions possible (50%) as seas
near 5 feet.

Thursday Night through Friday....Small Craft Advisory conditions
likely (60-70%) on the coastal waters as seas build toward 5 to 6
feet. Gusts near 25 kt as well, which may necessitate an SCA for the
Delaware Bay.


Rip currents...

For Monday and Tuesday, east winds will average 15 to 20 mph
with breaking waves of 2 to 4 feet with an 8 to 9 second
period. This results in a HIGH risk for the development of
dangerous and life threatening rip currents for the Delaware
Beaches and Jersey Shore. A Rip Current Statement is now in
effect for both Monday and Tuesday.

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

&&

.TIDES/COASTAL FLOODING...
Continued onshore flow will result in some minor tidal
flooding, mainly along the Atlantic coast and within the
Delaware Bay. Coastal Flood Advisories were issued for tonight`s
high tide for coastal locations in South Jersey and southern
Delaware. For the Delaware Bay, a Coastal Flood Advisory was
issued for Cumberland County, NJ and Kent, DE. For the upper
Delaware Bay, tidal Delaware River, and central and northern NJ
coast (north of Atlantic County), only spotty minor flooding is
expected for tonight`s high tide.

As we get into the middle of the week, water is
anticipated to continue to pile up in the back bays and up the
Delaware River with prolonged onshore flow. This may result in
further advisories as early as Tuesday evening. However, only
minor flooding is expected at this time. Will let the current
advisories for Monday night run their course before deciding on
an extension and/or expansion of the Coastal Flood Advisory.

No tidal flooding is expected along the Eastern Shore of
Maryland currently.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...Coastal Flood Advisory from 6 PM this evening to midnight EDT
     tonight for NJZ021>025.
     High Risk for Rip Currents through Tuesday evening for NJZ024.
     High Risk for Rip Currents through Tuesday evening for NJZ014-025-
     026.
DE...Coastal Flood Advisory from 6 PM this evening to midnight EDT
     tonight for DEZ002>004.
     High Risk for Rip Currents through Tuesday evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory from noon today to 6 PM EDT Tuesday for
     ANZ431.
     Small Craft Advisory from 8 AM this morning to 6 AM EDT
     Wednesday for ANZ450.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ451>455.

&&

$$

SYNOPSIS...Hoeflich
NEAR TERM...MJL
SHORT TERM...Hoeflich
LONG TERM...AKL/Hoeflich
AVIATION...Hoeflich/MJL
MARINE...Hoeflich/MJL
TIDES/COASTAL FLOODING...Hoeflich