NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Sep 23, 4:44 AM EST, 16 minutes earlier.
Area forecast discussion, Sep 23, 4:44 AM EST, 16 minutes before
Area Forecast Discussion
National Weather Service Mount Holly NJ
544 AM EDT Sat Sep 23 2023
.SYNOPSIS...
High pressure is giving way to Tropical Storm Ophelia approaching
from the south. Ophelia will weaken to a remnant area of low
pressure over the weekend while tracking across our region, 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 TONIGHT/...
Tropical Storm Ophelia is nearing the North Carolina coast early
this morning. Have made some refinements to the forecast through
tonight based on the latest observation and model trends, but
overall the expected impacts to our local area remain unchanged from
earlier forecasts, and no changed to hazards/headlines were needed.
High pressure extending from Nova Scotia to New England will
gradually give way and slip eastward while Ophelia approaches from
the south. Ophelia will weaken steadily while tracking inland, and
begin to transition to an extratropical cyclone while drifting over
eastern Virginia tonight. In any case, the classification of the low
pressure system will not be critical as far as sensible weather and
impacts go for our region; the key factor will remain the strong
pressure gradient between the low and the high to the north, which
will be driven to a certain degree by the strength of the low. As
the low weakens and approaches our region later today and tonight,
the strongest pressure gradient will weaken as well while shifting
northward. Winds are already gusting near 50 mph along Delaware's
Atlantic Coast, with near 40 mph gusts along the NJ shore during the
predawn hours. These winds will continue to ramp up further over the
next several hours, peaking this morning across most of our region.
High Wind Warnings remain in effect for coastal zones through this
afternoon, where the most exposed sites near the beaches may briefly
gust to 60 mph this morning. Wind Advisories remain in effect for
many adjacent inland zones. The advisories for interior Delaware and
eastern Maryland might be a little marginal, but the latest HRRR at
least suggests that gusts of 40 to 45 mph my occur briefly there
later this morning and into early afternoon. As the tighter gradient
shifts northward and weakens, winds will lessen somewhat this
afternoon along most of the coast south of Barnegat Light,
especially toward Delaware. However, more generally windy conditions
with gusts still 20 to 30 mph will linger into tonight; locally
higher along the Monmouth and Ocean County coasts.
We have continued to slow the forecast arrival time and amounts of
rain 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,
with 'heavier' rain rates pushing northwest across Delaware into
southern NJ (still only up to 0.25 inches per hour). Meanwhile, rain
will overspread the region this morning, but rates do not appear too
impressive. Some areas along the DE and NJ coastal plain,
particularly toward coastal NJ, may see 1/2 inch or more in 3-6
hours, but this should be nothing that will cause any flooding
issues. Aside from the winds and coastal flooding, we will have to
keep an eye on thunderstorms trying to track northwestward off the
ocean into the Delmarva and around Cape May to perhaps Atlantic City
this afternoon into this evening. Especially if just enough
instability becomes available, storms will be capable of rotation,
and a waterspout or two may try to make it onshore with discrete
stronger storms.
Additionally, with a more humid airmass and convective environment
in place, there may be some potential for heavier rain around the
Delmarva into far southern NJ this afternoon and this evening,
perhaps over an inch per hour. However, that will still be far below
flash flood guidance, so at most there might be some localized
minor/brief flooding in poor-drainage areas. The heavy rain,
however, may exacerbate coastal flooding that will occur during
times of high tide. Otherwise, across much of the northern 2/3 of
our area from Philly northward, rain will actually tend to become
more intermittent from midday through this evening. As what's left
of weakening/transitioning Tropical Storm Ophelia tracks across
Virginia toward the Chesapeake tonight, additional rain will tend to
overspread more of the area tonight...but still, the threat for
heavy rainfall looks rather limited. That's not to say we will see
quite a bit of rain over the course of the weekend...as we are still
looking at 2 to 3 inch totals through Sunday in most spots. Even
with the breaks in the rain, it will be a cloudy, inclement day with
the brisk winds, with downright hazardous conditions near the
immediate coast. Highs will only be in the 60s for most of the area,
with muggy conditions and low to mid 70s in far southern coastal NJ
and southern Delaware.
&&
.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
Models still aren't in full agreement on the path or
progression of the remnants of Ophelia as it tracks northward
towards our area Sunday before turning and slowly meandering
north and east across our region. General consensus from the
GFS/ECMWF/GEM in the latest round of guidance is to have the
center of the low turn to the right as it crosses the Chesapeake
Bay then move east- northeasterly across Delmarva and
southeastern New Jersey before meandering off the coast. The NAM
is a bit of an outlier in this round of guidance, continuing
with the more north-northeasterly track across New Jersey. In
any case, frontal banding on the north side of the decaying low
is expected to provide continuing rain, possibly heavy at
times, and breezy conditions on Sunday especially across our PA
and NJ areas. Depending on the exact track of the low, there
remains some concern for additional heavy rainfall in our
southeast PA counties especially. The 00z guidance, including
available CAMs, continues to hint 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. This upslope effect may be
minimized somewhat by the more southerly track but stronger
forcing along the immediate front could still allow for
a similar enhancement in rainfall totals. Will have to continue
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 /TUESDAY 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 /09Z SATURDAY THROUGH WEDNESDAY/...
Through 12Z...VFR ceilings lower to MVFR, with some IFR possible
near 12Z, especially MIV/ACY. Rain will overspread most of our area
by morning, from south to north, light at first, then becoming
moderate and steadier with visibility dropping to around 2 to 4 SM.
Northeast winds 10-15 knots with some gusts 20-25 knots, increasing
to 15-20 with gusts 20-30 knots (strongest at KMIV/KACY). Exact
timing and extent over any IFR CIG/VSBY is low confidence.
Rest of today...MVFR/IFR conditions along with periods of rain.
VSBY may improve to VFR this afternoon in some areas, but IFR
ceilings may linger much of the day. Northeast winds 15-25 knots
with gusts 25-45 knots (strongest at KMIV/KACY). Moderate confidence.
Tonight...IFR with periods of rain and low ceilings. Northeast winds
12-20 kt with gusts lingering around 25 kt or so, at least through
the evening. 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.
&&
.MARINE...
Tropical Storm Ophelia will move into the Carolina coast early this
morning. NE winds early this morning around 25 to 30 kt with gusts
40 to 45 kt will continue to increase through this morning as the
pressure gradient tightens further, to 25 to 35 kt with 45 to 50 kt
gusts. As the stronger pressure gradient shifts northward to north
of Barnegat Light later this afternoon, winds to the south will
ease, and we will probably be able to drop to Small Craft Advisory
for most zones through tonight for most zones. However, wind gusts
north of Barnegat will linger 35 to 40 kt into this evening, as well
as locally around upper Delaware Bay. Winds should continue to drop
tonight, from the E or ENE 10-20 kt by morning, but locally up to 25
kt sustained possible still off the Monmouth County coast early
Sunday morning.
Meanwhile, seas have cracked 15 ft at Buoy 9 this morning, and will
remain at least 10 to 15 feet on the ocean today before subsiding to
8 to 12 feet tonight. On Delaware Bay, seas build to 6 to 8 feet
today before subsiding to 3 to 5 feet tonight.
VSBY restrictions in moderate to heavy rain will be likely, and some
thunderstorms will be possible from near Atlantic City southward
this afternoon into tonight. Would not rule out an isolated
waterspout.
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 tonight, a HIGH risk continues for life-threatening rip
currents for the Delaware and New Jersey beaches. Onshore winds 30-
40 mph with gusts to 50-60 mph. Breaking waves also increase to 6 to
10 feet, even locally higher, with a building easterly swell near 12-
14 ft. A High Surf Advisory is in effect through tonight as a result
of the greater than 8-foot breaking waves.
For Sunday, a HIGH risk of life-threatening rip currents will
persist as a coastal storm continues to impact the region. Winds
will subside substantially tonight into Sunday, but will remain
generally onshore E/SE 12 to 20 kt on Sunday. Seas will lower, but
will still result in breaking waves in the 5 to 7 ft range along
much of the NJ shore, but a bit lower near Cape May to the Delaware
Beaches. The HIGH risk of rip currents may even continue into Monday
for at least a portion of the area, particularly north of
Brigantine.
&&
.TIDES/COASTAL FLOODING...
No changes to Coastal Flood headlines with the latest update.
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. Tidal levels are running
a touch higher than the previous forecast so values were
generally increased slightly but overall remain similar. 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...
PA...Coastal Flood Advisory from 7 PM this evening to midnight EDT
tonight for PAZ070-071-106.
NJ...Coastal Flood Advisory from 4 PM this afternoon to 9 PM EDT
this evening for NJZ016.
Coastal Flood Warning from noon today to 8 PM EDT this evening
for NJZ020-022>027.
High Wind Warning until 6 PM EDT this evening for NJZ024>026.
High Risk for Rip Currents through Sunday evening for NJZ014-
024>026.
High Surf Advisory until 4 AM EDT Sunday for NJZ014-024>026.
Coastal Flood Advisory from 1 PM this afternoon to 7 PM EDT
this evening for NJZ012>014-021.
Wind Advisory until 6 PM EDT this evening for NJZ013-014-020-
022-023-027.
Coastal Flood Advisory from 7 PM this evening to midnight EDT
tonight for NJZ017>019.
DE...Coastal Flood Advisory from 4 PM this afternoon to 9 PM EDT
this evening for DEZ001.
Wind Advisory until 6 PM EDT this evening for DEZ002-003.
Coastal Flood Warning from noon today to 8 PM EDT this evening
for DEZ002>004.
High Wind Warning until 6 PM EDT this evening for DEZ004.
High Risk for Rip Currents through Sunday evening for DEZ004.
High Surf Advisory until 4 AM EDT Sunday for DEZ004.
MD...Wind Advisory until 6 PM EDT this evening for MDZ012-015-019-
020.
Coastal Flood Advisory from 11 PM this evening to 4 AM EDT
Sunday for MDZ015-019-020.
MARINE...Gale Warning until midnight EDT tonight for ANZ430.
Gale Warning until 6 AM EDT early this morning for ANZ431-
450>455.
Storm Warning until 6 PM EDT this evening for ANZ431-450>455.
&&
SYNOPSIS...Dodd
NEAR TERM...Dodd
SHORT TERM...AKL/Brudy
LONG TERM...DeSilva
AVIATION...AKL/Dodd
MARINE...AKL/Dodd
TIDES/COASTAL FLOODING...WFO PHI