Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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FXUS61 KPHI 201942
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
342 PM EDT Wed Sep 20 2017

.SYNOPSIS...
Tropical Storm Jose will be meandering well offshore through this
weekend as it gradually weakens. High pressure centered to our north
and west will slowly build closer to our area later this week and
into the weekend. A weakening Hurricane Maria should parallel the
East Coast offshore during early next week, while a cold front
approaches from the west during Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The center of Tropical Storm Jose was located about 270 miles east
of Atlantic City this afternoon. This system is expected to move
slowly to the east-northeast tonight. Our region will remain
positioned on the western fringe of Jose`s counterclockwise
circulation and to the east of a weak surface ridge along the
Appalachians.

Visible satellite imagery shows enhanced CU on the western fringe of
Jose`s cloud shield over southeastern PA, southern NJ and DE. Weak
boundary-layer convergence seems to be promoting the CU development,
but with a relatively stable airmass (owing to warm mid levels),
convective development should be too shallow to support much more
than an isolated shower (or more likely just sprinkles) before
sunset.

Northerly winds 10-15 mph this afternoon will become light after
sunset this evening. Boundary-layer decoupling would be favored in
the typical sheltered river valleys of northeastern PA and
northwestern NJ, where there is a potential for radiational fog,
especially toward early morning. Low temperatures will generally
be in the 60s area wide.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Large-scale pattern for Thursday very similar to today. Tropical
Storm Jose is expected to stall several hundred miles off the NJ
coast while high pressure ridges southward down Appalachian spine.

Northerly winds should be a few mph lower than today while
temperatures are expected to trend upward by a degree or two owing
to less cloud cover tomorrow. High temperatures in the mid 80s will
be around 10 degrees above normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Summary...A warm pattern through this time frame with a cold front
not scheduled to arrive until during Wednesday. Tropical Storm Jose
meanders well offshore for awhile, then monitoring Hurricane Maria
as it should weaken northward as it parallels the East Coast
offshore the first half of next week.

Synoptic Overview...A strong ridge is forecast to extend from the
Lower Mississippi Valley northeastward to the Great Lakes and toward
northern New England through Friday, which then shifts eastward some
over the weekend. This ridge should gradually weaken over the
weekend into next week as a trough aloft shifts from the western
states into the Plains and Midwest. The placement of this ridge and
another one near Bermuda will result in very weak steering flow,
therefore Tropical Storm Jose is forecast to meander around well
east of our coast. Meanwhile, a weakness in the aforementioned
ridges as well as the placement of Jose will have an affect on where
Hurricane Maria goes as it turns northward. We used a blend of model
guidance and continuity for Thursday night through Friday night,
then used mostly the 12z WPC Guidance.

For Thursday night and Friday...An upper-level ridge is forecast to
build some more just to our west and north, which results in strung
out surface high pressure. This surface high gradually builds south
and eastward, however its progress will be slowed due to Tropical
Storm Jose meandering offshore. Jose is forecast to be centered well
east of our coast, however its circulation will maintain a northerly
wind for our area. Jose currently has a large cloud canopy
associated with it therefore as it lingers, at least the eastern
parts of our area could see more cloudiness (mainly the high level
variety). Despite the ridge aloft not all that far to our and west
Friday, some western influence of Jose could keep our temperatures a
little cooler. Overall though, most places are expected to get into
the 80s Friday afternoon. The western extent of Jose`s moisture
should continue to remain well east of our area.

For Saturday and Sunday...A rather stuck weather pattern is in place
with a ridge that slowly builds a bit to the east. Meanwhile, Jose
should still be well east of our coast although it should be
spinning down. There could be more clouds at times over the weekend
especially closer to the coast given the proximity to the western
part of Jose`s circulation. Depending on the steering currents, Jose
could make a turn more toward our coast late Sunday. It appears
though that any showers will continue to remain east of our region,
therefore carried a dry forecast through the weekend.

For Monday through Wednesday...This time frame could end up being
more challenging as we watch two tropical systems. The first is Jose
which is forecast to become post tropical as it spins down off the
northern Mid Atlantic coast. Some guidance wants to push its
remnants into our area Monday, particularly as the system weakens
quite a bit vertically allowing the low-level feature to be steered
more westward. We are not certain this will happen at this time as
our attention also turns southward to Hurricane Maria. For now,
included some slight chance PoPs for much of the area Monday into
Tuesday.

The track of Maria looks to be partially determined by where Jose
goes and if it weakens faster and if Jose is able to help produce a
weakness in the ridging (one to the north and west and another near
Bermuda). While the consensus overall is to keep Maria offshore of
the East Coast, especially as we get into Tuesday and Wednesday,
influence from an incoming upper-level trough begins to occur. The
timing of this trough will also be important. The presence of
Hurricane Maria (which should weaken with a northward extent) looks
to be a little close for comfort, therefore monitor the forecasts
from the National Hurricane Center and our office for the latest.
Pending no showers from dwindling Jose early next week, warm weather
should prevail. A cold front does not look to approach until later
Wednesday which will also potentially help to keep Maria off the
coast. We followed WPC closely and did not go even warmer given more
uncertainty with the details especially tied to the tropical activity.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.

VFR TAF issued at 18Z with one exception:  Vsby may briefly drop to
MVFR or lower at RDG just before sunrise Thursday with the
expectation that patchy radiational fog forms in the typical fog-
prone valleys of NE PA. Do not think other TAF sites should see
radiational fog with a light breeze for most of the night.

Wind direction will vary between N-W and N-NE through the period.
Speeds will be in the 5-12 kt range with gusts 15-20 kt this
afternoon, becoming 5 kt or less tonight, then 5-10 kt during the
day Thursday.

Outlook...
Thursday night and Friday...VFR. Northerly winds 10 knots or less
during the day, then mostly light and variable at night.

Saturday through Monday...VFR overall. Winds favoring between
northwest to northeast generally 10 knots or less.

&&

.MARINE...
Small Craft Advisory continues for our coastal Atlantic waters for
the remainder of this afternoon, tonight and Thursday. Winds have
steadily decreased throughout the day and are generally in the 10-20
kt range late this afternoon. We may eventually be able to
transition to a Small Craft Advisory for Hazardous Seas at some
point this evening (especially for southern waters) but decided it
was better to hold off at this point with isolated gusts near 25 kt
(and to avoid over complicating headlines). Seas, which are
currently in the 6-8 ft range at our offshore buoys this afternoon,
will continue to subside to 4-6 ft tonight into Thursday.

Outlook...
Thursday night and Friday...Northerly winds should remain below
Small Craft Advisory criteria, however seas will remain elevated as
Tropical Storm Jose meanders well offshore. Therefore, the Small
Craft Advisory has been extended through the day Friday.

Saturday through Monday...A continued northerly wind through this
time frame, however it is anticipated to be below advisory criteria.
Seas may subside some as Jose weakens, however building swells from
Hurricane Maria should arrive with time.

Rip Currents...
Tropical Storm Jose will continue to push long period (9-12 second)
E-NE swells toward the shoreline this afternoon through Thursday.
Will continue to carry the high risk for dangerous rip currents
for the rest of today. The risk should lower to a moderate risk
tomorrow with waves in the surf zone several feet lower than
today and with light northerly winds.

The risk may drop to moderate for Friday with waves subsiding a
bit and winds lighter. However, long period swells from Hurricane
Maria should arrive this weekend which could raise the risk to
high once again.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies remain steady between 1.25 and 1.75 ft above
astronomical prediction. Additionally, a new moon tonight has
resulted in higher astronomical tides. Will keep the Coastal Flood
Advisory for coastal NJ and DE (including the oceanfront, back bays
and Delaware Bay) for the next high tide cycle tonight. We also
added Talbot, Caroline and Kent Counties along the eastern shore of
Maryland to the Coastal Flood Advisory for the impending high tide
late this afternoon-early evening.

There is a potential for additional minor coastal flooding to
persist into the high tide cycles on Thursday but confidence in
reaching advisory threshold is low at this point. It looks more like
spotty minor tidal flooding as the wind field weakens across the
area.

We do not anticipate any tidal flooding with today or tonight`s high
tide along the Delaware River upstream from the Commodore Barry
Bridge area or on the upper eastern shore of Chesapeake Bay.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
PA...None.
NJ...High Rip Current Risk until 9 PM EDT this evening for NJZ014-
     024>026.
     Coastal Flood Advisory until 1 AM EDT Thursday for NJZ012>014-
     020>027.
     Coastal Flood Advisory until 2 AM EDT Thursday for NJZ016.
DE...High Rip Current Risk until 9 PM EDT this evening for DEZ004.
     Coastal Flood Advisory until 1 AM EDT Thursday for DEZ002>004.
     Coastal Flood Advisory until 2 AM EDT Thursday for DEZ001.
MD...Coastal Flood Advisory until 9 PM EDT this evening for MDZ015-
     019-020.
MARINE...Small Craft Advisory until 6 PM EDT Friday for ANZ450>455.

&&

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



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