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Area Forecast Discussion (AFD)

Issued by Philadelphia/Mt Holly (PHI)

FXUS61 KPHI 191638

Area Forecast Discussion
National Weather Service Mount Holly NJ
1238 PM EDT Thu Sep 19 2019

High pressure will gradually build southward into the Middle  
Atlantic region through the end of the week. Hurricane Humberto 
will continue to move to the northeast, well away from our waters. 
The high will weaken and move offshore during the weekend as an area 
of low pressure and cold front approaches the region from the west.


Winds have been a little stronger this morning, but they are
starting to settle down. A few shallow cumulus along the shore
will continue to move inland across South Jersey with a crisp 
onshore flow a little stronger than forecast. Otherwise a nice 
afternoon in store.

Previous discussion..
The main story of today will be that the center of the large 
surface high which has been to our north for the last few days, 
will build south over our region, and eventually south of our 
region by tonight. Meanwhile, in the mid and upper levels, a 
short wave ridge will shift over our region from the northwest. 
As a result, we will have subsidence across the region leading 
to mostly sunny conditions through the day. Another result is 
that the persistent onshore flow (which has persisted for the 
last few days) is expected to weaken through the day, becoming 
light and variable by late this afternoon.

Like yesterday, temperatures will be slightly below normal, with 
highs mostly in the upper 60s to lower 70s.


As mentioned above, the center of the surface high will finally 
shift south of our region by tonight. As a result, the winds (after 
being variable through the afternoon and into the evening) will 
become westerly, brining our first prolonged period of off shore 
flow since Sunday.

With very dry conditions, light winds (especially in the evening), 
and mostly clear skies, we will have prime conditions for 
radiational cooling. Therefore, expect temperatures tonight to be 5 
to 10 degrees below normal. With the exception of the urban centers 
and coastal locations, most of the region is likely to drop into the 
40s overnight.


Nice weather will continue for Friday and into the weekend as the 
surface high builds over the area. The high will not be in a hurry 
to leave as the upper high also remains nearby. Temperatures will 
warm to near normal Friday and then go mostly above normal for the 
weekend. In fact, highs will be up to 10 degrees above normal in 
many areas. Humidity levels will rise a bit, but it shouldn't become 
too uncomfortable. Sunny days and mostly clear nights expected. A 
little valley fog possible each morning. 

Next week, the high will have weakened sufficiently to allow a cold 
front to approach from the west. Pops are slight chc for the N/W 
areas Monday and then increase for Mon night before decreasing Tue. 
The upper trough accompanying the sfc front will be rather progressive,
so only light amts of rain are presently expected. Highs will still
be well above normal Mon (mostly mid 80s) but then readings will
drop back to closer toe normal by mid-week. Fair weather is
expected Wednesday.


The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, 
KMIV, KACY and surrounding areas.

Today...VFR conditions are expected. Winds will start
northeasterly with a few gusts near or above 10 knots possible
at times. Was not confident enough to put this in the TAFs,
however. By this afternoon, winds will begin to be light and 

Tonight...VFR conditions are expected to continue. Winds will start 
light and variable, but should eventually settle out of the west, 
with speeds staying well below 10 kt.

Sat thru Sunday night...A continuation of mostly VFR conditions 
across the terminals. A little early morning fog possible however. 

Sunday thru Tuesday...Mostly VFR. Sct showers with lower conditions 


On the Atlantic Coastal waters: The Small Craft Advisory remains in 
effect. Elevated seas will continue today and tonight. Wind gusts 
above 25 kt are also possible through the morning, but we should see 
winds gradually diminish this afternoon. 

On the Delaware Bay: Winds and waves should mostly stay below SCA 
criteria. The one exception is right at the mouth of the bay, waves 
near or just above 5 feet will be possible through this morning. 
Since it will be confined to a very small area right at the mouth of 
the bay, have chosen to cover this hazard with a marine weather 


Friday/Friday night...SCA conditions will continue as the swells 
from Humberto will still be affecting the waters. Fair weather

Sat/Sunday...Fair weather with high pressure across the waters. SCA 
conditions not expected to last into Sat morning, so we will not 
extend the SCA flag any further in time.  

Mon/Tue...More sub-SCA conditions, but a few showers possible Monday 
night and Tue morning. 

Rip Currents... 

A HIGH risk for the development of dangerous rip currents is 
expected through this evening due to elevated seas and also swell 
energy (wave period around 10 seconds) from Hurricane Humberto. Wave 
heights in the surf zone are expected to be up to 7 feet today.

An enhanced rip current risk (either moderate or high) will likely 
continue through at least Saturday due to continued long period 
swells from Humberto.


NJ...High Rip Current Risk until 11 PM EDT this evening for NJZ014-
DE...High Rip Current Risk until 11 PM EDT this evening for DEZ004.
MARINE...Small Craft Advisory until 8 AM EDT Saturday for ANZ450>455.


Near Term...Davis/Johnson
Short Term...Davis/Johnson
Long Term...O'Hara