416
FXUS61 KPHI 162338
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
738 PM EDT Mon Sep 16 2024

.SYNOPSIS...
High pressure will be in control through tonight. One area of low
pressure tracks northwestward into the Carolinas while a secondary
low passes off to our east, bringing increasing chances for showers
across our area through midweek. Unsettled conditions persist
through the end of the week as high pressure tries to build in for
next weekend and early next week.

&&

.NEAR TERM /THROUGH TUESDAY/...
No significant changes with the early evening update. High
pressure to the northeast continues to weaken allowing an
increased onshore flow with added moisture to continue over the
area. Areas of rain currently remain well to the south of our
region. However, later this evening, we may see the first
showers begin to move into northern Delmarva. On Tuesday the
pops continue to increase, reaching up into central NJ and the
Lehigh Valley of PA. Overall QPF is expected to be less than a
tenth of an inch for tonight and Tuesday, with the highest
totals across Delmarva. Lows tonight will remain on the mild
side with the onshore flow and clouds in place. Readings will
fall to the mid/upper 60s for the S/E areas and mid/50s to low
60s elsewhere.

On Tuesday, it`ll continue rather cloudy as the onshore flow
continues scattered showers are expected, especially for the
southern half of the CWA, as moisture associated with a low pressure
system approaches. Up across the far north, breaks in the clouds and
some limited sunshine is possible. Highs on Tuesday will be similar
than todays with mid/upper 70s common. Winds will be Northeast to
East around 10 mph.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
The remnants of Potential Tropical Cyclone 8, its associated
tropical moisture, and a secondary coastal low will be the main
talking points of the short term period. Tropical moisture will
be advected north during the term resulting in periods of heavy
rain supported by several shortwaves embedded in the upper flow.

The first wave still looks to be on pace to affect the region late
Tuesday night into the day on Wednesday. This will be associated
with a secondary coastal low that develops off the Carolinas
separating itself from the upper low associated with PTC8. This
secondary low will lift northward paralleling our coastline while
remaining offshore. The biggest difference at this point amongst
models, is just how far offshore this secondary low will be. If the
low, takes a closer track to the coast, then more in the way of
heavy rain looks plausible during the day on Wednesday. If the track
is further offshore as indicated by some guidance, there may be
enough dry air filtering in from the north to keep any beneficial
rainfall offshore. Regardless, PWATs are forecast to be around 2
inches, so some tropical related downpours are possible through the
period. In terms of the flood risk, the risk really isn`t that high
due to the dry conditions that have occurred over the past couple of
weeks. This is supported well by the Weather Prediction Center which
now keeps only southern NJ and the Delmarva in a Marginal Risk for
Excessive Rainfall on Wednesday.

Heading into Wednesday night and Thursday, the forecast varies
significantly due to the fact that global and short-range guidance
are struggling to depict the upper pattern. The GFS keeps an open
deep trough over the East Coast, while the ECMWF closes the trough
into a closed low which meanders overhead. So, while there is
potential for showers to continue into Wednesday night and Thursday,
the confidence in this in actually occuring is low. As a result,
have kept a 20-40% chance of showers across the entire region during
this period. Storm total rainfall through Thursday is expected to be
around 0.50-1.00 inches from the I-95 south and east with roughly
0.25-0.50 inches north and west of I-95.

In terms of temperatures, we are looking at highs in the 70s on
Wednesday and Thursday with lows in the 60s thanks to the tropical
airmass in place.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The blocking pattern aloft will likely continue as a deep trough
will remain within the vicinity of the East Coast through much of
the period. This will yield unsettled and cool conditions through
the end of the week, before turning potentially more tranquil to
kick off the weekend into next week.

As of now, most of the deterministic guidance keeps the deep upper
trough over the East Coast through about Saturday before an upper
ridge begins to move over the top into early next week. This will
keep the threat for showers and cool weather to occur through
Friday, before high pressure builds to our north and east for
Saturday onwards. While there will still be a chance of a shower or
two over the southern portions of the area, for the most part the
forecast is trending drier for the weekend and into early next week.
However, with blocking patterns, weather features are often
difficult to predict, so there likely will be some variance to the
forecast in the coming days.

In terms of temperatures, most of the region does appear to stay on
the cooler side of normal with temps mostly in the 70s during the
day and in the 50s at night.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

Tonight...In general, expect ceilings to lower into MVFR for
most of the TAF sites. Less certain if we will see IFR ceilings
anywhere given the relatively brief window (according to most
guidance) for saturated boundary layer. Most guidance depicts
the window of saturated boundary layer only through about 09Z
for most sites. This however, seems suspect given that it would
be very unusual timing to see improvement. Another source of
uncertainty is that higher clouds are masking the extent of the
low clouds on satellite imagery. Currently though,it appears
the low clouds extend from KMJX to KPHL. This should continue to
spread further west and north overnight. Not sure yet if it
will reach KABE or KRDG. East to Northeast winds around 10 knots
decreasing to around 5 kts overnight. Low confidence,
especially with the timing and extent of low clouds.


Tuesday...Any lingering MVFR ceilings should improve to VFR by
15Z. There is a slight chance (20%) of showers generally after
18Z for most TAF sites, but haven`t included it in the TAFs, and
even if they do develop, expect minimal impact. East winds
increasing to around 10 knots. Moderate confidence.

Outlook...

Tuesday night through Thursday...Sub-VFR conditions likely with
periods of rain and isolated thunderstorms. Locally heavy rain is
possible at times especially Tuesday night into Wednesday.

Thursday night through Saturday...Primarily VFR expected. Slight
chance for a shower or thunderstorm which may cause temporary
restrictions.

&&

.MARINE...
SCA conditions will continue across the waters, save the upper
Delaware Bay, tonight and Tuesday. East to Northeast winds around 15
kts with gusts 25 to 30 kts expected. Seas will be generally 5 to 8
ft. Fair this evening then scattered showers possible for the
Delaware waters late tonight and all waters for Tuesday.

Outlook...

Tuesday night through Wednesday night...SCA conditions to continue
due to elevated seas around 5-6 feet. As a result, there will
likely will need to be an extension to the current SCA in
effect.

Thursday...SCA conditions possible as seas will be around 4-5 feet.

Thursday night through Saturday...SCA conditions likely to redevelop
with seas building from 4-6 feet to 6-8 feet. Winds may gust up to
30 kt on Saturday as well.

Rip currents...

For 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. For Wednesday, east winds will decrease slightly to
around 15 mph but breaking waves remain 2 to 4 feet with an 8 to
9 second period. Therefore, the HIGH risk for the development
of rip currents was maintained for Wednesday. As a result, a Rip
Current Statement is now in effect for both Tuesday and
Wednesday.

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

&&

.TIDES/COASTAL FLOODING...
Continued onshore flow and higher astronomical tides with the
full moon on Tuesday will result in some minor tidal flooding,
mainly along the Atlantic coast and within the Delaware Bay.
No changes were made to the Coastal Flood Advisories issued for
tonight`s high tide for coastal locations in South Jersey and
southern Delaware. For the Delaware Bay, the 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 tonight 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 until midnight EDT tonight for
     NJZ021>025.
     High Risk for Rip Currents through Wednesday evening for NJZ014-
     024>026.
DE...Coastal Flood Advisory until midnight EDT tonight for
     DEZ002>004.
     High Risk for Rip Currents through Wednesday evening for DEZ004.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ431.
     Small Craft Advisory until 6 AM EDT Wednesday for ANZ450>455.

&&

$$

SYNOPSIS...DeSilva/Hoeflich
NEAR TERM...Johnson/OHara
SHORT TERM...DeSilva/Hoeflich
LONG TERM...DeSilva/Hoeflich
AVIATION...DeSilva/Johnson/OHara
MARINE...AKL/DeSilva/OHara
TIDES/COASTAL FLOODING...AKL/Hoeflich