Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 300957

Area Forecast Discussion
National Weather Service Mount Holly NJ
557 AM EDT Fri Sep 30 2016

A frontal boundary will remain stationary to our south today
through Saturday with high pressure to our north, and an area of
low pressure to our west. The high pressure will begin to break
down Saturday night into Sunday. The low to our west will then
lift through the Great Lakes region and into the northeast over
the weekend, before weakening on Monday. This will pull the
frontal boundary across our area Sunday. High pressure builds to
our north for Tuesday into Thursday with a northeast flow across
the area.


Updated the winds based on current trends. With the latest obs, it
looks like winds are well on their way to diminishing across the
southern half of the region. In addition...based on observations
overnight, it is unlikely that wind advisory criteria will reach
very far inland. Thus...have canceled the wind advisory for all
but the central and northern NJ shore.

Previous near term discussion...Subtle shift in the flow,
primarily in the mid level flow will cause the axis of highest
precipitable water to shift north through the day today. As such,
many models are depicting a lull in precip for the southern half
of our region. However, given how poor models have been handling
this event so far, this remains a very low confidence forecast.
Even with a lull or light precip in Delmarva, flooding issues
could continue as many creeks continue to rise due to the precip
over the last 36 hours (see hydrology section).

As for temperatures, continue to see little swing in diurnal
temperatures due to the precip and persistent cloud cover. Expect
highs to generally be within 10 degrees of the low temps this


The mid level flow shifts a bit more southwesterly overnight,
this will decrease the moisture advection somewhat. Additionally,
the pressure gradient will continue to relax, meaning low level
flow will drop off sharply through the overnight hours. With very
limited instability, expect all precip overnight to be stratiform
and light.


Unsettled weather continues to be forecast for much of the
extended period, especially into the weekend.

By Saturday, and especially Sunday, the high to our north begins
to move eastward, and the low to our west will begin lifting back
toward the Great Lakes region. This will eventually pull the
frontal boundary to our south across our area on Sunday. There
will continue to be a chance of showers Saturday through Sunday as
several short wave/vorticity impulses move across the area as the
closed low aloft begins to break down and lift to the northeast.

On Monday, the mid-level low will be moving across the area, and
the surface low to our north will weaken as it moves into New
England. As the mid-level low crosses the area, there could be
some scattered showers affecting the area Monday into Monday

For Tuesday into Thursday, high pressure builds to our north and
noses its way across our area. With the high to our north, an
onshore flow will develop again, which may end up leading to more
cloud cover and cooler conditions. The mid-level trough continues
to slowly move across the area Tuesday, which could keep a chance
of showers across the area. By Wednesday and Thursday, the trough
moves eastward, but with the northeasterly flow and continued
moisture, there could be some light rain or drizzle across the

The focus beyond the extended turns to Hurricane Matthew. The
current tracks from the long term guidance is for the system to
make the turn to the right and away from the coast before reaching
our area. We will need to continue monitoring the forecast over
the next several days for adjustments to the forecast track.


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

Ceilings should generally be hovering between 700 and 1500 ft AGL
through much of the TAF period. Some guidance shows a several
hours lull in precip through the day. If this comes true, some
locations may see temporary improvement to VFR ceilings through
the day time hours. However, ceilings are expected to lower once
again near or after 00Z.

Winds will stay northeasterly through the TAF period. Wind speeds
should decrease through the day from SW to NE (KACY will likely be
the last TAF site to see gusts drop off).

Saturday-Saturday night...A prolonged period of MVFR or IFR
conditions with periods of rain is expected to affect the TAF
sites through the period. East to northeast winds are expected to
gust 15-20 knots on Saturday.

Sunday-Monday...Some improvement, possibly to VFR. Showers remain

Monday night-Tuesday...MVFR or IFR conditions likely to return.
Showers remain possible again. East to northeast winds are expected to
gust 15-20 knots on Tuesday.


Winds along the bay and the far southern coastal waters are below
gale. Thus...replaced the gale warning with a small craft advisory.

Gale conditions continue on the NJ coastal waters, but winds are
expected to decrease through the day. Once winds drop below gale
conditions, a small craft advisory will likely be needed for the
rest of today and tonight due to both wind gusts near 25 kt and
lingering high seas.

Saturday...Winds expected to drop below Small Craft Advisory
levels, however, seas may remain above advisory levels through the

Saturday night-Sunday...Winds and seas expected to drop below Small
Craft Advisory levels.

Sunday night-Monday night...Conditions expected to remain below
Small Craft Advisory levels.

Tuesday...Small Craft Advisory conditions may return to the waters.


There is a high risk for the formation of dangerous rip currents
along the NJ shore and the DE beaches today. Wave heights should
slowly diminish through the day.


Under normal circumstances, the precip amounts that nearly all
guidance is depicting for today and tonight would not be enough to
cause flooding issues, and given the lack of instability through
the day, expect this event to be transitioning to more of a
stratiform event. However, with some locations in Sussex County DE
now with over 12 inches of rain over the last 36 hours, even light
rain amounts could exacerbate ongoing flooding issues especially
in central and southern Delaware. Therefore, have kept the flood
watch going through 20Z.

As the mid level flow shifts more southwesterly through the
overnight hours tonight, moisture advection should decrease, and
precipitation should continue to decrease.


Minor tidal flooding is expected with the morning high tide cycle
for all but the tidal Delaware River. Based on tidal departures we
saw with the last high tide cycle, water levels this morning
should be solidly in the minor category, but fall short of
moderate thresholds (this morning`s high tide is the lower of the
astronomical tides).

As for the high tide cycle this evening, tidal flooding concerns
will depend, to a large part on how quickly the winds drop off
through the day today. For now, am forecasting that winds will
drop off quickly by mid day (except along the far northern shore)
which should lessen the threat for this evening`s high tide. This
will need to be revisited through the day.


Georgetown broke its daily rainfall record with 6.52 inches. Here
are today`s rainfall records.

Sept 30

ACY 1.76 1964
PHL 2.41 2010
ILG 4.32 2010
TTN 1.50 1924
GED 3.15 1964

This section below will update on Friday.

September will be/is a top 10 warmest month through most of our
forecast area, for the 3rd consecutive month!

Also September will be/is enjoying a second consecutive top 5
warmest month in the period of record for PHL and ABE.

We`ve run the actual numbers through the 28th, then added the
forecast high/low for 29th and 30th.

Philadelphia: Expect a 73.8 degree average or about 5 degrees above
the monthly normal of 69.1. This will be a #4 or #5 warmest
September on record for Philadelphia.

Philadelphia September average temperature rankings

75.4 -1881
74.5 -2015
74.1 -1931 74.1 -1930
73.8 -2005 and 2016 #4

(small chance PHL avg will be 73.7 or #5 ranking)
72.9 -2010 72.9 - 1921

Philly ranked #7 warmest July followed by a warmest ever August in
the POR dating back to 1874.

Atlantic City: Expect a 71.2 degree monthly average temperature, or
4 degrees above the monthly normal of 67.2. This would equate to
an 8th warmest September in the period of record dating back to 1874.
Atlantic City recorded a #7 warmest July and then a warmest ever

73.3 - 1961
72.8 - 1881
72.3 - 1931 and 1930
71.7 - 1921
71.6 - 2015
71.5 - 1933
71.3 - 2005

71.2 - 2016 #8
71.0 - 2010
70.6 - 2011 and 1906

Allentown: Expect a monthly average of 69.4 degrees, or 5.5
degrees above the monthly normal of 63.9 and a 4th warmest
September on record. Allentown ranked 8th warmest July and #2
warmest August in the period of record.

70.8 - 1961
70.3 - 1980
69.7 - 2015
69.4 - 1931 and 2016

(small chance Allentown will rank #5 at 69.3 degrees)

68.7 - 2005


PA...Flash Flood Watch until 4 PM EDT this afternoon for PAZ070-071.
NJ...High Rip Current Risk through this afternoon for NJZ014-
     Flash Flood Watch until 4 PM EDT this afternoon for NJZ016>027.
     Coastal Flood Advisory until noon EDT today for NJZ012>014-
     Wind Advisory until noon EDT today for NJZ014-025-026.
     Coastal Flood Advisory from 10 AM this morning to 1 PM EDT
     this afternoon for NJZ016.
DE...High Rip Current Risk through this afternoon for DEZ004.
     Flash Flood Watch until 4 PM EDT this afternoon for DEZ001>004.
     Coastal Flood Advisory until noon EDT today for DEZ002>004.
     Coastal Flood Advisory from 10 AM this morning to 1 PM EDT
     this afternoon for DEZ001.
MD...Flash Flood Watch until 4 PM EDT this afternoon for MDZ008-012-
MARINE...Gale Warning until noon EDT today for ANZ452-453.
     Gale Warning until 2 AM EDT Saturday for ANZ450-451.
     Small Craft Advisory until 11 PM EDT this evening for ANZ454-
     Small Craft Advisory until noon EDT today for ANZ430-431.


Near Term...Johnson
Short Term...Johnson
Long Term...Robertson
Tides/Coastal Flooding...
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