Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 301954
Area Forecast Discussion
National Weather Service Mount Holly NJ
354 PM EDT TUE AUG 30 2016
High pressure will move offshore tonight before giving way to a cold
front approaching from the northwest on Wednesday. This front will
move through the area Wednesday night. Behind the cold front, high
pressure will build southeast into the Great Lakes and New England.
Tropical depression nine currently in the gulf is expected to move
northeast tracking offshore over the holiday weekend with high
pressure anchored to our north through early next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Persistent area of isolated, but locally heavy, showers impacting
parts of SE NJ through this evening due to the combination of
onshore flow and weak low pressure developing over northern DE.
Latest HRRR has those showers tapering off around 21Z. Will carry an
area of chance pops for those areas for several hours into early
this evening, and then precip should come to an end as that low
As for the rest of the CWA, dry conditions on tap through the
forecast period. Clouds should dissipate through this evening with
loss of diurnal heating. Low level moisture will continue to
increase with a light easterly flow, and surface dewpoints will
slowly creep up during the overnight hours. As a result, can expect
patchy fog to develop away from the major urban centers.
Lows tonight will be several degrees above normal for this time of
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
High pressure over northern New England continues to push offshore
on Wednesday. Meanwhile, weak low pressure tracking across Canada
will drag a weak cold front through the Ohio Valley and towards
northern NJ in the afternoon. H5 trough with several embedded
shortwaves will follow thereafter, approaching mainly northern NJ
late in the day. For most of the day, the energy and support for
showers and thunderstorms will occur over northern areas, so will
carry chance POPs across SE PA and into northern NJ. For the rest of
NJ and into DE/MD, will only carry slight chance POPs, mainly for
the late afternoon.
In addition, Tropical Depression 8, currently just south of Cape
hatteras, may strengthen to Tropical Storm, but is forecasted to
pass well to the southeast of the Delmarva before tracking into the
western Atlantic waters.
Highs on Wednesday will once again be 5-7 degrees above normal, with
highs in PHL possibly touching 90 once again.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Wednesday night and Thursday: A cold front will approach the
region from the northwest. Ahead of this front moisture will be
advected into the region. Modeling may be to quick with the
moisture advection, especially given the recent dry pattern.
However, enough moisture and lift looks present along this front
for the formation of a band of showers and a couple of
thunderstorms to move from northwest to southeast across the
region. A few heavy downpours would be possibile (PW ahead of
front 1.5-1.75 inches). Strong to severe thunderstorms are not
anticipated given both the GFS and ECMWF are only advertising a
few hundred J/KG of CAPE ahead of this front along with a
overnight event. Showers and isolated thunderstorms should end
across the southern portions of the region during the day
Thursday. QPF of a quarter to half inch seems reasonable as well,
with the SREF, WPC and the WRF NMM/ARW models used for the QPF
forecast. High temperatures Thursday will likely end up a few
degrees below MOS guidance given the cloudcover with highs around
80 in most places.
Thursday night through Tuesday: High pressure will build eastward
into New England and remain in place or slowly shift east through
early next week. Temperatures look to be several degrees cooler
through the weekend, with a warming trend early next week. If it
were just this high pressure system as a potential influence on
our weather, sunny skies with a dry holiday weekend will occur.
However, TD 9 is a potential factor as well. The GFS, GEFS, UKMET
and Canadian models all have this feature slowly tracking up the
coast, stalling it to our south or even turning back to the
northwest. This would increase cloudcover, winds and the prospects
for rain as you get closer to the coast. The ECMWF up till the
30/12 run has been fairly consistent with having TD 9 get carried
out to sea with the trough which brings a cold front through on
Thursday. Overall, a lot of uncertainty is present around the
weekend time period. Given the building ridge this weekend the
potential is present for this system to get trapped somewhere
close to our region. However, will not commit fully to the new
trend yet given it is only set of model runs.
.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
VFR forecast for all terminals through 00Z Wednesday. SCT-BKN deck
at 040-060 will persist through this evening, and then skies clear
out with loss of differential heating. A few sprinkles are
possible at KACY/KMIV through around 21Z.
E to SE winds will generally range from 5-10 KT.
After 00Z Wednesday, predominantly a VFR forecast with the
exception of patchy ground fog developing after 09Z. For most
terminals, conditions may fall to MVFR, but cannot rule out patchy
IFR stratus, especially at KMIV.
Fog dissipates after sunrise Wednesday. VFR thereafter with light
Cold front approaches on Wednesday. SCT SHRA/TSRA possible in the
afternoon, mainly for northern NJ terminals, but cannot rule out ISO
SHRA/TSRA approaching KPHL late.
Wednesday night and Thursday: Mainly VFR, with some MVFR
restrictions possibile in any heavier showers or isolated
thunderstorms. Southwest winds around 10 knots shifting to
northwest, higher gusts Thursday afternoon.
Thursday night through Friday night: VFR. Northerly winds around
Saturday and Sunday: Considerable uncertainty in this period of
the forecast due to currently TD 9. If TD 9 stays offshore
(currently most likely) VFR throughout with winds generally under
15 knots. Lower ceilings and higher winds if we see impacts from
TD 9, KACY and KMIV have highest chances currently.
Wave heights came close to 5 feet with long period swells, but going
into tonight, wave heights will begin to subside, and will expect 3
to 4 ft seas through Wednesday.
Cold front slowly approaches the waters on Wednesday, and isolated
showers and thunderstorms are possible in the afternoon.
Water temps are generally in the 70s, which is above normal.
Thursday through Sunday: Seas gradually building heading into the
weekend. Seas of a couple of feet and northerly winds at or under
15 knots through Friday. Considerable uncertainty with how high
the seas get in relation to the track of TD9 for the weekend. Seas
right now look to be at or above SCA criteria from Friday night
from Sunday. Northeasterly SCA gusts are possibile in this
timeframe as well.
With 3 to 4 foot long period swells across the ocean and an easterly
flow, the rip current risk through this evening remains moderate.
For Wednesday: Wave heights may slowly decrease during the day, but
with 12-13 second period swells, will continue with the potential
for moderate risk of dangerous rip currents.
Will reissue the Beach Hazards Statement highlighting the risk for
swells from Gaston and then a probable renewal of moderate to high
risk rip current formation conditions between Friday and Labor day.
This in part based on NHCs outlook compared with the cyclic
continuity of GFS/EC operational model cycles.
Thursday: RC risk probably eases back to low enhanced.
Friday-Sunday: RC risk increases with cool boundary layer wind transfer
as high pressure develops to our north, with an ensembled fairly
extensive broad easterly fetch developing south of New England.
Likely to be moderate or higher depending on the track of TD9.
In terms of safety, follow the advice of local lifeguards who will
be observing the waves and swimmers. There may be some beach closures,
all dependent on the reality that develops. This is not a time to
swim on your own without lifeguard presence. Additionally, waders
are cautioned not to turn their backs to the waves when coming out
of the water. Wave knock down can result in upper torso injury
(dislocations/spinal cord injuries).
Spotty minor tidal flooding is possibile late this week into the
weekend with the high tide cycles. However, this is also dependent
on the track of TD 9. A track closer to the coast could increase
This section is up to date through 3 AM Today-Tuesday August 30.
A top 4 warmest August appears assured most of our forecast area
with record monthly warmth likely at PHL.
A top 3 warmest June-July-August for Philadelphia, Allentown and
possibly Atlantic City.
Philadelphia will establish its warmest August on record (dating
back to 1874). More than 4 degrees above normal.
This Philadelphia August ranking includes our forecast temps (SFT
specific values) through the 31st. The 30 year normal is 76.6
Records date back to 1874.
1. ~81.0 2016
2. 79.9 1980
3. 79.8 2001 and 1995
Regarding whether August can tie its record of 17 90F days. Its
possible. Today is the critical day for extending the heat wave.
The record of 17 was set in 1995. The mean for the month is only
5. Tomorrow reaching 90 at PHl looks to be relatively easy.
Allentown will rank #2 warmest August. Records date back to 1922.
Normal is 71.7 and we are projecting a positive departure of
around 5 degrees.
1. 78.2 1980
2. ~76.6 2016
3. 76.0 1937
Atlantic City records date back to 1874. The August monthly normal
is 74.4 and we`re projecting a positive departure of nearly 4
degrees. As it stands, Atlantic City will rank #1 warmest August
with very little chance of slipping to #2. The forecast and climate
for Atlantic City has greater variability than Allentown and
Philadelphia due to proximity to water on sea breeze days and
notable radiational cooling on some nights.
1. 78.2 2016
2. 77.9 2005
3. 77.1 2009
Seasonal: This summer 2016 for Philadelphia will probably be the
2nd warmest June-July-August (JJA) in the period of record dating
back to 1874.
1. 79.6 2010
2. 78.8 2016
3. 78.6 1995
4. 78.3 1994
Allentown seasonal avg is projecting 75.0 or a ranking of around
#2 in the por.
1 75.3 1949
2 75.0 2016
3 74.6 2005 and 1980
Atlantic City seasonal average is projecting 75.8...4th warmest
in the por.
1. 77.5 2010
2. 77.0 2011
3. 75.9 2005
4. 75.8 2016
5. 75.5 2008
90 degree days through the 29th.
season mean Aug Aug Aug Season
mean rer rer
ABE 33 17 12 4 16-1980 41-1966
ACY 28 10 11 3 11-2010 46-2010
PHL 39 21 15 5 17-1995 55-2010
ILG 33 20 14 5 23-1895 59-1895
Rainfall: Some uncertainty exists regarding additional rainfall
in August, so this part of the climate is stated with caution.
Presuming no further measurable rain this month of August...the
current ACY value of 1.10 would rank the 6th driest August on
record, after a 6th wettest July.
For Philadelphia, the June-August seasonal total of 7.45 inches
is so far, the 12th driest summer...again this presumes no further
measurable rain in August.
NJ...Beach Hazards Statement through Wednesday evening for NJZ014-
DE...Beach Hazards Statement through Wednesday evening for DEZ004.