Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 161833
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
233 PM EDT Sat Sep 16 2017

.SYNOPSIS...
Weak high pressure will build over our region through Sunday.
Hurricane Jose is forecast to move northward off the mid-
Atlantic coast through mid week, passing near our region Tuesday
into Wednesday. High pressure is expected to once again build
over our region late in the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A weakening trough aloft will continue to be over our area through
tonight. There remains a fairly large area of strung out short wave
energy associated with it. A mesoscale analysis this afternoon
indicates surface-based CAPE ranging from 500-1200 j/kg across the
region, with the highest focused across northern New Jersey and
portions of eastern Pennsylvania. The flow is on the light side and
despite disorganized lift, some showers will continue through late
this afternoon. The shower development has been mostly focused to
terrain, then the activity is sliding southwestward due to a weak
northeasterly flow. This activity is tied to daytime heating,
therefore we are expecting them to dissipate very early this evening.

As we go through tonight, there are some mixed signals regarding the
development of stratus and fog. The setup looks to be conducive for
both given the light flow and no real change in the airmass. As the
boundary layer cools, saturation is expected for many areas and this
would point to fog development assuming no clouds above. There was
some stratus along parts of our coast this morning, and this has
since dissipated although there is some lurking just south of Long
Island this afternoon. Given the light onshore flow, this area of
low clouds should advect west and southwest some through the night.
Some guidance is not all that robust with this, perhaps due to the
weak flow, but shows some fog, while other guidance indicates
stratus gets to at least the coastal areas. Since the flow is not
all that strong, we favored stratus development for the coastal
areas especially. Farther inland however may end up having more fog
especially if there are no clouds aloft. Given the mixed signals, we
carried a fog mention however did not include dense fog.

Low temperatures are mostly a MOS/continuity blend. The hourly
temperature, dew point and wind grids were initially adjusted based
on the latest observations, then the LAMP and some high-res guidance
was blended in through the evening.

&&

.SHORT TERM /SUNDAY/...
A similar setup for Sunday as some ridging occurs across the
Northeast, although a weakness still exists as a trough aloft
remains across our region. Given the lighter flow, stratus and/or
fog will dissipate during the morning although this may be slower
along the coastal areas (assuming it is in place to start).

Once any fog and/or stratus dissipates, we should have a similar day
compared to Saturday with cumulus development occurring by late
morning. Given the onshore flow, this may leave the coastal locales
with more sunshine compared to inland during the afternoon (assuming
any stratus/fog dissipates). Once again some showers cannot be ruled
mainly in eastern Pennsylvania to northern New Jersey where terrain
should assist in some development. We are not expecting much
coverage given a lack of overall forcing and flow, and again should
be low-topped and therefore left out a thunder mention. We continued
with some low mentionable PoPs during the afternoon.

High temperatures are mainly a blend of MOS and continuity.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
The main story remains Hurricane Jose and its pass off our coast
next week.

Monday through Wednesday...Please see the forecast discussion
from the National Hurricane Center for the latest details on the
forecast track of Hurricane Jose. For our area, we are still
looking at a track with the center passing about a few hundred
miles off shore, though still close enough for some impacts to
our region. At this point, we are expecting most of the impacts
on Tuesday, though it should be noted there are still large
timing differences between the models. As for the impacts for
our region:

Wind: With the latest track, it appears unlikely, though not
impossible, that our land areas will see winds of tropical
storm force. That being said, Tuesday into Wednesday will be
quite breezy at the shore.

Coastal Flooding: Please see the section below on the potential
for coastal flooding Monday into Tuesday night.

Heavy Rain: Current track keeps the heavy rain off shore on
Tuesday, with our area only seeing the outer rain bands.
However, any additional rain at the shore near or shortly before
a high tide could exacerbate coastal flooding.

Rip currents: Please see the discussion under the marine section
for details on the rip current risk.

Thursday and Friday...Most of the operational models depict a
high amplitude ridge beginning to build over the region through
this period, but it remains uncertain how quickly this will
build. In addition, if it develops far enough north, we could
be in a on shore low level flow regime for our area, tempering
any warming trend due to the increasing thicknesses.

&&

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

This afternoon...VFR with cloud bases in the 3,500-5,000 feet range.
Isolated to scattered showers will be around mainly north and west
of KPHL. Winds light and variable, or locally light from the
southeast.

Tonight...Any showers end early, then some fog and/or stratus should
develop initially in the KACY and KMIV areas. There is less
certainty how far inland the stratus gets as it may be more fog. If
less stratus develops, then fog may end up becoming more widespread
with significant visibility restrictions. Winds light and variable
to locally calm.

Sunday...Fog and/or stratus dissipates in the morning, then VFR. A
few inland afternoon showers cannot be ruled out mainly north and
west of KPHL. East to northeast winds less than 10 knots, possibly
turning locally southeast in the afternoon.

Outlook...
Sunday night...Another round of fog with visibilities of MVFR
or lower is possible, but details are uncertain at this time.

Monday-Tuesday...Expect conditions to deteriorate to MVFR or
lower across most of the region especially Monday night into
Tuesday as Jose passes near our coast. KABE and KRDG may stay
VFR for much of the period as they may be west of the main rain
shield. Breezy easterly winds are possible for much of the
region, with KACY having the highest risk of gusts above 30 KT.

Wednesday...Becoming VFR with decreasing northwest winds.

&&

.MARINE...
The winds are expected to be well below Small Craft Advisory
criteria through Sunday. However, swells are expected to gradually
build through Sunday due to distant Hurricane Jose. This should get
seas into the 5-6 foot range through Sunday and therefore the Small
Craft Advisory for Hazardous Seas goes into effect early this
evening for the ocean zones. Some locally dense fog is possible
later tonight and early Sunday morning, mainly nearshore.

Outlook...
Sunday...SCA conditions are expected primarily for seas above 5
feet and primarily for the coastal waters and lower Delaware
Bay.

Monday through Wednesday...Tropical storm conditions will be
possible Tuesday. However, even by Monday morning, winds will be
above SCA criteria in advance of Hurricane Jose approaching from the
south.  Although winds will begin to diminish Wednesday, it will
take time for seas to subside.

Rip Currents...
Swells of 3-4 feet with a period of around 12 seconds combined with
an onshore flow (although on the light side), is resulting in a
moderate risk for the development of dangerous rip currents through
tonight. The swells should build a foot or so during Sunday, which
results in a moderate to possibly even high risk. This will be re-
evaluated this evening.

A moderate or even high risk is expected through at least mid week
as we continue to see the swells from Hurricane Jose reach our
shores.

&&

.TIDES/COASTAL FLOODING...
Coastal flooding is possible with the high tide cycles Monday
through Tuesday night due to the passage of Hurricane Jose.

A prolonged period of east to northeast winds will allow water to
pile up along the shores. In addition, there is a new moon on
Wednesday, September 20, so astronomical tide levels will be running
high.

Depending on how close Jose tracks to the coast changes how
significant the coastal flooding will be. As of now, minor coastal
flooding is likely with the high tide cycles from Monday afternoon
through Tuesday night. If Jose tracks closer to the coast, then
widespread moderate coastal flooding will become more likely. If the
timing of Jose slows down, then high tide cycles on Wednesday may be
affected as well.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...None.
DE...None.
MD...None.
MARINE...Small Craft Advisory for hazardous seas from 6 PM this evening
     to 6 PM EDT Sunday for ANZ450>455.

&&

$$
Synopsis...Johnson
Near Term...Gorse
Short Term...Gorse
Long Term...Johnson
Aviation...Gorse/Johnson
Marine...Gorse/Johnson
Tides/Coastal Flooding...



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