679 
FXUS61 KPHI 021749
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
149 PM EDT Sat Sep 2 2023

.SYNOPSIS...
High pressure will remain parked over the area through 
today. A weak shortwave passes by tonight as high pressure 
slides to our south over the southern Appalachians and 
southeastern states through Wednesday. A cold front approaches 
the area late in the week bringing the potential for some 
showers and a cool-down.

&&

.NEAR TERM /THROUGH SUNDAY/...
The surface high continues to slide south. A mid level short
wave trough will cross through the northeastern U.S. overnight,
but with little in the way of moisture in place, expect to
remain dry through the near term period. The only impacts of
this will be some increasing mid level clouds tonight with the
trough, and increasing southwesterly flow in the low levels. 

One consequence of the low level southwesterly flow will be a
warming trend that will kick off tomorrow and continue into much
of the new week. For tomorrow, expecting highs to range from the
mid 80s to lower 90s (still well below daily record values). 
With an expected deep mixing layer, have gone slightly below the
model consensus blend for dew points. The result of which is 
that heat index values will be very close to air temperatures. 
Consequently, although Sunday will feel like a bit of a shock 
compared to the last few days, we should stay well below heat 
advisory criteria at this time.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
Upper level ridge will be building just to our west over the
Ohio and Tennessee Valleys Sunday night through Monday night.
However, a weak shortwave will ride around the northeastern side
of the ridge during this period. There does not appear to be a
surface boundary associated with this shortwave, though warm
advection will be ongoing. Guidance shows some spotty precip
with this little shortwave, but given exceedingly low coverage
and lack of consistency among models, have kept any mention of
precip out of the forecast for the time being. 

Otherwise, the main story will be the building heat. The surface
high will shift southward, providing a generally westerly flow 
across the region at the surface, which generally is downslope.
850 temps will rise up towards 22 C by late Monday, and while an
isolated shower is not impossible, overall cloud coverage looks
low, so insolation should be high. Thus, widespread mid 90s look
like a good bet, which will certainly challenge records.
Fortunately, dew points don't look overly high, mostly staying
in the 60s, so that should keep heat indices generally below 100
across the region. The nights either side also don't look
particularly oppressive, with lows mostly in the 60s Sunday 
night, but around 70 on Monday night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
Upper level ridge slowly crosses the area Tuesday through
Thursday, slowly weakening as it does so, but keeping
temperatures elevated during this time with high pressure to the
south and generally westerly surface flow. Some guidance wants
to bring a weak cold front southward for Tuesday, but other
models reject this idea, and most still hold 850 temps above 20C
through Thursday. Thus, will keep a dry and hot forecast Tuesday
and Wednesday, ramping down slowly Thursday as the next more
potent cold front approaches, then a more noticeable drop Friday
with a better chance of showers and storms. Still not a great
deal of confidence the further out in time given model
discrepancies and uncertainty about how all the tropical systems
in the Atlantic might disturb the pattern, but for now it looks
like the best bet.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, 
KILG, KMIV, KACY and surrounding areas.

Through Tonight...VFR. Any ceilings will remain above 10k ft
AGL. Winds may vary at times between S and SW, but should be
prevailing SW less than 10 kt. High confidence.

Sunday...VFR with only some high clouds. Winds shifting from SW
to W less than 10kt. The exception is at KACY where an afternoon
sea breeze may keep winds SSW near 10kt. High confidence.


Outlook...
Monday...VFR. Winds W to NW 5-10 kts. High confidence. 

Tuesday...VFR. Winds N 5-10 kts. High confidence.

Wednesday...VFR. Winds NW 5-10 kts. High confidence.

&&

.MARINE...
Winds and seas are expected to remain below Small Craft 
Advisory conditions through Sunday.

Outlook...
Monday...sub-SCA conditions. Winds W, becoming S around 10 kts.
Seas 2-4 ft. 

Tuesday...sub-SCA conditions. Winds N to E around 10 kts. Seas
2-3 ft. 

Wednesday...sub-SCA conditions. Winds N, becoming S around 10
kts. Seas 2-4 ft.


Rip currents...

A variable wind around 5 MPH on this morning is anticipated to 
become southeast to south 5 to 10 MPH in the afternoon along the
coasts of Delaware and New Jersey. Breaking waves should be 3 
to 4 feet with a long period (around 10 second) swell from the 
east, mainly from Idalia. As a result, we will continue to carry
a HIGH risk for the development of dangerous rip currents.

For Sunday, winds turn more south/southwesterly which is more
shore parallel rather than onshore. However, with breaking waves
around 2 to 4 feet, a long period swell persisting, and multiple
swell groups present, we have elected to keep the HIGH risk for
the development of dangerous rip currents going for another day. 

Idalia will remain well off the Middle Atlantic and New England
coasts through the end of the holiday weekend. It will likely 
continue to send long period swells our way, along with an 
enhanced rip current risk.

&&

.TIDES/COASTAL FLOODING...
All Coastal Flood Advisories have been allowed to expire. The 
wind is expected to become southerly for Saturday and Sunday. 
Ekman transport will begin to push water away from our coast 
gradually. Also, the astronomical high tides will continue to 
decrease. No additional tidal flooding is expected for Saturday 
and Sunday.

&&

.CLIMATE...
Near record breaking heat is forecast for Monday thru 
Wednesday. Records for our climate sites are listed below:

Record High Temperatures
                        Sept 4          Sept 5          Sept 6
Site               Record/Year     Record/Year     Record/Year
Allentown (ABE)        94/1937         94/2018         96/1983
AC Airport (ACY)       96/2018         93/1985         98/1983
AC Marina (55N)        92/1985         94/1880         92/1985
Georgetown (GED)       97/2008         93/2018         93/2018
Mount Pocono (MPO)     88/1973         85/2018         88/2018
Philadelphia (PHL)     93/2018         95/2018         95/2018
Reading (RDG)          94/2008         93/2018         95/1943
Trenton (TTN)          95/1929         95/1985         99/1983
Wilmington (ILG)       95/2018         93/2018         98/1983

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...High Risk for Rip Currents through Sunday evening for NJZ014-
     024>026.
DE...High Risk for Rip Currents through Sunday evening for DEZ004.
MD...None.
MARINE...None.

&&

$$

SYNOPSIS...Hoeflich/RCM
NEAR TERM...Johnson
SHORT TERM...RCM
LONG TERM...RCM
AVIATION...Johnson/RCM
MARINE...Johnson/RCM
TIDES/COASTAL FLOODING...
CLIMATE...