-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPHI 230200
AFDPHI

Area Forecast Discussion
National Weather Service Mount Holly NJ
1000 PM EDT Fri Sep 22 2023

.SYNOPSIS...
High pressure exits tonight, giving way to Tropical Storm
Ophelia approaching from the south. Ophelia will impact the area
throughout the weekend, before departing on Monday. High
pressure builds over Canada and the Northeast US through the
middle of the week. Unsettled weather looks to return late in
the week.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
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Tropical Storm Ophelia continues to approach the North Carolina
coast. Impacts to the local area remain unchanged.

As of 950 PM, continued to slow the PoP increase quite a bit
this evening from south to north as the initial rain shield is
running into a drier air mass. This has resulted in some
breaking up of the rain, however a moisture surge is working
northward now across Delmarva. The 00z Wallops Island, VA RAOB
showed that the precipitable water has increased to 1.53 inches.
Tweaked the temperature, dew point and wind grids to keep them
current based on the latest observations/trends. Wind gusts to
around 40 mph are ongoing along the Delaware Atlantic coast, and
this will increase overnight and Saturday morning (also spread
northward).

Otherwise, high pressure will be entrenched over the Canadian
Maritimes, Gulf of Maine, and into New England tonight before
moving into the Western Atlantic on Saturday. Meanwhile, Ophelia
moves into the Mid-Atlantic tonight and will meander over North
Carolina Saturday before lifting towards Delmarva Saturday
night. A 40 to 50 kt low-level jet will spin off of Ophelia and
will lift through the region late tonight through Saturday.
Combined with a tight pressure gradient between the departing
high and Ophelia, a period of strong and potentially damaging
winds will develop tonight through Saturday. East winds will
generally average 20 to 30 mph with 30 to 40 mph gusts, however,
gusts as high as 60 mph will spread along the New Jersey and
Delaware coasts, and gusts as high as 50 mph will develop into
the eastern shores of Maryland, most of Delaware and along and
east of the Garden State Parkway in New Jersey. High Wind
Warnings remain in effect for the coastal zones, and Wind
Advisories remain in effect for eastern New Jersey and most of
Delaware. Also, a Wind Advisory has been issued for the eastern
shores of Maryland at the same time as Delaware. Northeast
winds diminish Saturday night as the gradient relaxes as the
high departs and the low-level jet departs.

Although rain will move into the southern portions of the
forecast area this evening, periods of moderate to heavy rain
will spread through the region from south to north towards
daybreak Saturday and into Saturday afternoon. The heaviest rain
bands are shaping up to impact southern Delaware and eastern
New Jersey. Overall, 2 to 4 inches of rain will fall in these
areas, with about 3/4 to 1.5 inches elsewhere through Saturday.
An additional 1/2 to 1 inch of rain is possible in the coastal
plain Saturday night with lesser amounts elsewhere.

Isolated thunderstorms possible through Saturday, but as that
remnant low lifts closer to the region Saturday night, there is
a better chance for thunderstorms, mainly in the southern third
of the forecast area.

Flash Flood Guidance values are fairly high where the heaviest
rain will fall. Across the coastal plain of New Jersey, 6 hour
FFG values are 4 to 6 inches, and less rain than that is
expected to fall tonight through Saturday night. The heavy rain,
however, may exacerbate coastal flooding that will occur during
times of high tide.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
Models still aren`t in full agreement on the path or
progression of the remnants of Ophelia as it tracks northward
across the Chesapeake Sunday and slowly meanders north and east
across New Jersey. General consensus is in said track, but with
timing differences as the GEM is much more progressive than the
GFS/ECMWF/NAM suite which are slower and provide continuing
rain, possibly heavy at times, and breezy conditions on Sunday
especially across our PA and NJ areas. If the center of the low
does slide up through the Chesapeake and slowly move through
eastern PA, there is some concern for additional heavy rainfall
in our southeast PA counties especially. The 12z guidance,
including available CAMs, are hinting at a period of easterly
wind on the north side of the low resulting in upslope flow and
localized higher amounts of rainfall across Chester, Berks,
Lehigh, Montgomery Counties. Will have to see how the rest of
the CAMs come in within the next 24 hours to get a better idea,
but the potential is there. Otherwise, rain is forecast to
gradually become more scattered through the day, though those
that do see breaks from the rain will still be left with thick
cloud coverage and a continuing breeze. Temperatures won`t move
much from overnight lows with highs topping out in the low to
mid 60s west of I-95 and upper 60s to low 70s south and east of
I-95.

Into the day on Monday, the low will continue to weaken and a
building ridge of strong high pressure located well off to our
north will try to suppress the northward extent of what`s left
of the low and its precipitation. A tightening gradient building
between the high and the low will result in increased
east/northeast gradient wind on Monday, though not as high what
we saw over the weekend with gusts looking to peak in the 20-25
mph range. With the onshore flow, expect that Monday will be
another dreary day and feature more thick cloud coverage and
showers, along with very little of a diurnal temperature range
as highs will only top out in the mid 60s.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The long term forecast has overall little change since the
previous forecast package as most of the guidance remains
relatively unchanged. The remnants of Ophelia drift east and
offshore Monday night. A few leftover showers may linger across
the area, so have kept a slight chance to chance (20-40%) of
showers through Tuesday.

A strong Canadian high out of Quebec then builds over the
northeastern US through Thursday. At upper levels, a troughing
pattern persists which may ultimately may become a blocky ULL
pattern through the end of the week. With the strong high in
place, the northern two-thirds of the forecast area should be
dry through Thursday. However, a surface trough develops
along/just south of the Mid-Atlantic coastline on Wednesday.
Thus, have opted to keep a 20- 30% chance of showers for
portions of the Delmarva and southern NJ. To end the week, the
high breaks down and signals of a cut-off ULL low to our west
yields an increase in the likelihood of precip to return to the
area into Friday.

Overall, below-normal temperatures should continue throughout
the long term period; generally in the mid-upper 60s to low 70s
for highs and upper 40s to mid-upper 50s for lows.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas...

Tonight...VFR ceilings lower to MVFR then to IFR late. Rain will
overspread the area overnight, light at first, then becoming
heavier with visibility restrictions. Northeast winds 10-15
knots with some gusts 20-25 knots, increasing to 15-20 with
gusts 20-30 knots (strongest at KMIV/KACY). Low confidence on
the arrival timing of the MVFR/IFR ceilings.

Saturday...MVFR/IFR conditions along with periods of rain. Northeast
winds 15-25 knots with gusts 25-45 knots (strongest at KMIV/KACY).
Moderate confidence.

Saturday night...IFR with some rain and stratus. Northeast winds
15-20 knots with gusts 25-30 knots. Moderate confidence.

Outlook...

Sunday...Sub-VFR conditions likely with showers. Easterly wind
10-15 knots with gusts to 20 knots. Moderate confidence.

Monday...Sub-VFR conditions possible with lingering showers.
Northeasterly wind 10-15 knots with gusts to 20 knots. Moderate
confidence.

Monday night...Primarily VFR. Sub-VFR possible especially
toward the coast. NE winds 10-15 kt with gusts up to 20 kt
possible. Low confidence.

Tuesday through Tuesday night...VFR. NE winds around 15 kt
gusting up to 20-25 kt during the day, becoming around 10 kt at
night. Moderate confidence.

Wednesday...VFR. NE-E winds around 10-15 kt with isolated gusts
up to 20 kt. Moderate confidence.
-- End Changed Discussion --

&&

.MARINE...
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Gale Warnings for tonight. Storm Warnings will take effect on
Saturday for all but upper Delaware Bay.

As of 950 PM, increased the wave heights a bit faster this
evening from south to north given observations from the buoys.
Gale force wind gusts are already occurring across the southern
Atlantic coastal waters and these will spread northward overnight
and increase.

Otherwise, Tropical Storm Ophelia will move into the Carolina
coast tonight. NE winds will increase to 20 to 30 kt tonight
with gusts up to 45 kt. Pressure gradient tightens further on
Saturday, and NE winds will increase to 25 to 35 kt with 45 to
55 kt gusts from Saturday morning through Saturday afternoon.
Winds on upper Delaware Bay will remain at Gale force.

Pressure gradient relaxes Saturday night. Gales expected in the
evening, but otherwise, SCA conditions will prevail.

Seas 8 to 12 feet tonight on the ocean and to 4 to 7 feet on
Delaware Bay. Seas then build to 10 to 15 feet on the ocean
Saturday before subsiding to 8 to 12 feet Saturday night. On
Delaware Bay, seas build to 6 to 8 feet on Saturday before
subsiding to 3 to 5 feet Saturday night.

VSBY restrictions in moderate to heavy rain.

Outlook...

Sunday...Small Craft Advisory conditions likely. East-
southeasterly wind 10-15 knots with gusts to 25 knots. Seas 8-10
feet decreasing to 6-8 feet in the afternoon.

Monday...Small Craft Advisory conditions likely. Northeasterly
wind 10-15 knots with gusts to 25 knots. Seas 5-7 feet.

Monday night...SCA conditions likely. NE winds around 15-20 kt
with gusts up to 25-30 kt possible. Seas 4-7 feet.

Tuesday...SCA conditions likely. NE-E winds around 20-25 kt
with gusts up to 30 kt. Seas 5-7 feet.

Wednesday...SCA conditions possible. NE-E winds around 15-20 kt
with gusts up to 25 kt. Seas 4-6 feet.

Rip Currents...

Through Saturday night, a HIGH risk continues for life-
threatening rip currents for the Delaware and New Jersey
beaches. Onshore winds increase to 30-40 mph with gusts to 50-60
mph. Breaking waves also increase to 5-9 feet with a continued
medium-long period swell. A High Surf Advisory is in effect for
Saturday into Saturday night as breaking waves are expected to
exceed 8 feet along much of the New Jersey and Delaware Atlantic
coast.

For Sunday, a HIGH risk of life-threatening rip currents will
persist as a coastal storm continues to impact the region. Breaking
waves and winds are currently forecast to peak on Saturday but
are expected to remain dangerous into Sunday as onshore flow
persists.
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&&

.TIDES/COASTAL FLOODING...
Coastal Flood Advisories have been extended to the tidal
Delaware River and for the Maryland counties of Talbot, Caroline
and Queen Anne`s for Saturday night.

A potentially significant coastal flood event is still forecast
for Saturday`s high tide along portions of Atlantic Coastal New
Jersey and Delaware, and Delaware Bay. The latest models
suggested water levels might be very slightly lower than the
last forecast, but we are still expecting moderate to locally
major flooding for areas from Barnegat Bay southward to Cape
May, and along the Kent and Sussex County (DE) coast. Coastal
Flood Warnings are in effect for those areas, with advisories
elsewhere. The exception is Kent County, Maryland on the far
upper eastern shore of the Chesapeake, where only spotty minor
flooding at most is expected, due to the strong northeast winds.

A strong onshore wind will increase reaching a peak on Saturday
midday. The greatest surge and tidal departures are forecast to
occur with the Saturday afternoon high tide along the coasts of
Kent and Sussex Counties in Delaware, and potentially along
coastal portions of Cape May and Atlantic Counties in New
Jersey.

The greatest threat for Major coastal flooding will be along
the coasts of Kent and Sussex Counties in Delaware, however some
spotty major flooding is possible in Cape May and Atlantic
Counties.

Modest onshore winds will persist Saturday night into Sunday as
the remnant low of Ophelia moves northward. This could result
in lingering minor coastal flooding with the Sunday high tides,
especially along back bays that do not drain well at low tide.
That may require some extension of warnings and advisories.

&&

.PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Coastal Flood Advisory from 7 PM Saturday to midnight EDT
     Saturday night for PAZ070-071-106.
NJ...Coastal Flood Advisory from 4 PM to 9 PM EDT Saturday for
     NJZ016.
     Coastal Flood Warning from noon to 8 PM EDT Saturday for
     NJZ020-022>027.
     High Risk for Rip Currents through Saturday evening for NJZ014-
     024>026.
     High Wind Warning until 6 PM EDT Saturday for NJZ024>026.
     High Surf Advisory from 6 AM to 8 PM EDT Saturday for NJZ014-
     024>026.
     Coastal Flood Advisory from 1 PM to 7 PM EDT Saturday for
     NJZ012>014-021.
     Wind Advisory from 6 AM to 6 PM EDT Saturday for NJZ013-014-
     020-022-023-027.
     Coastal Flood Advisory from 7 PM Saturday to midnight EDT
     Saturday night for NJZ017>019.
DE...Coastal Flood Advisory from 4 PM to 9 PM EDT Saturday for
     DEZ001.
     Wind Advisory until 6 PM EDT Saturday for DEZ002-003.
     Coastal Flood Warning from noon to 8 PM EDT Saturday for
     DEZ002>004.
     High Risk for Rip Currents through Saturday evening for DEZ004.
     High Wind Warning until 6 PM EDT Saturday for DEZ004.
     High Surf Advisory from 6 AM to 8 PM EDT Saturday for DEZ004.
MD...Wind Advisory until 6 PM EDT Saturday for MDZ012-015-019-020.
     Coastal Flood Advisory from 11 PM Saturday to 4 AM EDT Sunday
     for MDZ015-019-020.
MARINE...Gale Warning until midnight EDT Saturday night for ANZ430.
     Gale Warning until 6 AM EDT Saturday for ANZ431-450>455.
     Storm Warning from 6 AM to 6 PM EDT Saturday for ANZ431-
     450>455.
-- End Changed Discussion --

&&

$$

SYNOPSIS...DeSilva
NEAR TERM...Gorse/MPS
SHORT TERM...Brudy
LONG TERM...DeSilva
AVIATION...Brudy/DeSilva/Gorse/MPS
MARINE...Brudy/DeSilva/Gorse/MPS
TIDES/COASTAL FLOODING...WFO PHI