Locally heavy rain fell in parts of central and southern Delaware on the afternoon of September 11. Rainfall totals ranged from 2 to 4 inches.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PHI wrote it up.
Locally heavy rain fell in parts of central and southern Delaware on the afternoon of September 11. Rainfall totals ranged from 2 to 4 inches.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Sep 11, 12:25 PM EST, 1 hour 25 minutes earlier.
Area Forecast Discussion
National Weather Service Mount Holly NJ
125 PM EDT Tue Sep 11 2018
.SYNOPSIS...
The remnants of Tropical Cyclone Gordon are over the eastern
Great Lakes, and will continue to weaken as they track to the
north and east towards the Canadian Maritimes. This will drag a
cold front into the region this afternoon, and that front will
stall out along the coast and linger there through the middle of
the week. High pressure will build in from the north and west
on Wednesday. Impacts from Hurricane Florence are possible by
the end of the week and into the weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
No major changes with the 930 update. Fog should continue to
gradually dissipate through the morning hours. Didn't make any
changes to the temperatures or PoPs at this time, but if the
trends with the high res models continue both of those elements
may need to be tweaked down later today.
Previous discussion...
Showers and a couple storms developed near Chesapeake Bay early
this morning, with one storm affecting New Castle and Delaware
Counties for a brief period before the cell diminished. These
events suggest the long-awaited return of warmer/more unstable
air is beginning to occur, although models are about 24-30 hours
too fast. Still, I suspect this aggressive bias of the models
will continue, as the near-surface stable air poleward of the
warm front (still near or just south of our southern CWA
boundary) will be very difficult to scour. Trended temperatures
way downward in the northern third of the CWA again today
(possibly not enough). Trimmed max temps 2-5 degrees in most
spots except for the far south given the expected model bias, as
well.
In the meantime, fog and mist have developed in much of the
area this morning, and this will be slow to dissipate as the
morning progresses. Have continued fog mention early this
morning but have extended it through most of the rest of the
morning, as this environment will prove difficult to eradicate
given the thick/low stratus overhead.
Just how long this fog/mist last(s) and how far north the warm
sector makes it today will undoubtedly mar the forecast both
with temperatures and precipitation. Expect frequent adjustments
to temperatures as the attendant temperature gradient along the
front retreats northward. Moreover, instability will be
increasing (boundary-layer based near the front; elevated
everywhere). Models are nearly universally initiating convection
this afternoon somewhere near the Interstate 95 corridor
(perhaps with consensus slightly east of this axis). The
location of this convection will depend on the poleward progress
of the nose of the stronger instability, and knowing where this
ends up is extremely challenging. Remember, the warm front was
expected to retreat well into our CWA yesterday, resulting in
errors of 150+ miles within 12- 24 hours (i.e., not the greatest
forecast in the world).
What is more certain is that convection will develop in a very
moist (PWs > 2 inches) environment with little or no shear.
Corfidi vectors are very small, suggesting that convective
propagation may offset any cell motion that exists. There is a
fairly strong signal in model output that localized very heavy
rainfall is possible where the strongest convection develops.
Added heavy rain wording to the grids for today. A lack of more
widespread coverage and uncertainty on location given the above-
mentioned concerns precludes issuance of a flash flood watch.
Nevertheless, potential for instances of flash flooding exists.
The threat for severe looks quite low given questions regarding
amount of instability, weak shear, and unfavorable lapse rates.
Finally, a comment about a rather remarkable event that
occurred on Monday that was (in a theme) very poorly modeled
(and very poorly forecast by me). A region of surface confluence
developed near and just inland of the New Jersey shore, and a
long-duration steady rain fell for much of the day where the
confluence/convergence was maximized. This convergence was
likely a combination of surface friction (with strong winds
offshore decelerating and curving leftward in the statically
stable air on land) and a subtle theta-e gradient with an
associated wind-field response. Several locations in
Monmouth/Ocean Counties picked up 2 to 3 inches of rain as a
result of this near-steady-state boundary. This likely
exacerbated the coastal flooding that occurred in this area this
past evening, with several reports of road closures received
along the coast.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
The main forecast concern tonight is precipitation chances.
Overall, models appear to indicate that any convection will
diminish during the evening hours, but there are notable
exceptions. The 00Z NAM indicates a perturbation moving
northeastward around the northern Atlantic ridge that will
progress through the area this evening. This may keep
showers/storms going in the northern CWA this evening before
moving out of the area later in the night. As with any
convection that develops today, heavy rainfall may occur with
the strongest cells given the very moist profiles and relatively
slow storm motions and backward propagating effects.
Additionally, an upstream perturbation may move in later in the
night, and the NAM subsequently produces more precipitation
after midnight near the coast (with potential added
contributions from ambient convergence via surface friction and
subtle temperature/moisture gradients). Given the fairly similar
setup to what occurred on Monday in Monmouth/Ocean Counties,
may need to watch for the potential for some heavy rainfall
accumulations in this scenario. Notably, the WRF- ARW/NMM hint
at this, though with slower timing (more on Wednesday than
tonight) and with varying intensity.
Meanwhile, the 00Z RGEM is much slower to diminish convection,
which makes physical sense given the very moist environment
(harder to stabilize nocturnally). The depicted evolution of
convection is for a slow northward progression but with
potentially some heavy rainfall totals. The RGEM has 3+ inches
in northern portions of the CWA during this period. Other models
are generally way less aggressive with this potential, but
combined with the heavy rainfall concerns during the day, some
instances of flash flooding cannot be ruled out during the next
24 hours.
Kept PoPs generally in the chance range overnight given the
above potential scenarios. Additionally, with decreasing winds
and considerable low-level moisture, added mention of patchy fog
to the area late in the night. Regarding low temps, used a
consensus blend with additional input from some of the higher-
resolution model output given increased uncertainty owing to the
unclear evolution of convection after dark. Temperatures should
generally be about 7-12 degrees warmer than readings this
morning, but with obvious lower- than-average confidence.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
On Wednesday, high pressure continues to build and pass to the
north of the region. Onshore flow remains across the region,
resulting in surface dewpoints generally in the 60s in the
southern Poconos, and otherwise in the low to mid 70s. Highs
will generally top off in the upper 70s to low 80s, so it will
feel quite muggy. With the frontal boundary nearly stationary
along the Eastern Seaboard, but continuing to wash out, some
mid- level shortwave energy will move into the region, touching
off showers and scattered thunderstorms, mainly in the afternoon
and evening. Thunderstorms will be capable of locally heavy
rain is possible, as the high moisture content will result in
PWATs on the order of 2"-2.25".
From there, all eyes will be on Hurricane Florence as it
approaches the Southeast U.S. coast. Please refer to the
National Hurricane Center for the most up to date forecasts
regarding the track and intensity of Florence. There is still
a low-end probability for the risk for Tropical Storm Force
winds for extreme southern portions of the forecast area.
Regardless of whether Tropical Storm Conditions occur, there is
the chance for gusty onshore winds, heavy rain, and tidal
flooding for the end of the week and into the weekend.
Locally heavy rain also remains possible for the start of the
new week, depending on where the remnant low of Florence tracks.
&&
.AVIATION /17Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Rest of tonight...IFR/LIFR CIGs will continue at all terminals,
with occasional sub-VFR VSBYs likely. VSBYs may be reduced
under a half mile at MIV/ACY at times. In addition, showers have
developed near ILG and may approach the terminal (and even PHL)
through 10Z. Winds generally northeast under 8 kts, but may
become light/variable. High confidence.
Tuesday...Slow improvement to MVFR is forecast, and VFR
conditions may develop by afternoon at MIV/ACY/ILG/PHL. Showers
and storms are expected to develop during the afternoon.
Confidence in coverage/timing is high enough to begin mention in
the TAFs. Light northeast winds becoming more east to southeast
during the day, though variable directions should be expected
in general. Speeds under 10 kts, except near storms, where
stronger gusts are likely to occur. CIGs/VSBYs forecast is low
confidence; precip/wind forecast is moderate confidence.
Tuesday night...Conditions may deteriorate to MVFR/IFR,
especially near/west of PHL, during the night. Conditions at
MIV/ACY may remain VFR, though if CIGs become high enough,
patchy fog will probably develop. Isolated/scattered
showers/storms may occur, but confidence is too low for TAF
mention at this time. Light/variable winds. A very low
confidence forecast.
Outlook...
Wednesday...Generally VFR, but MVFR conditions are possible in
scattered showers and thunderstorms. Winds will be out of the
northeast/east around 5-10 knots.
Thursday through Saturday...Generally VFR, but MVFR conditions
are possible in scattered showers and thunderstorms. Winds will
be out of the northeast/east around 5-15 knots. Impacts from
Hurricane Florence are possible during this time.
&&
.MARINE...
Winds have diminished well below advisory criteria, as
southerly winds are attempting to become established on the open
Atlantic waters. However, residual effects of the long-
duration/strong onshore flow are keeping seas quite elevated.
Wave model forecasts are way underdone (generally by 2-3 feet).
I expect this bias to diminish today, but only gradually. Thus,
the forecast is for seas of 6-9 feet this morning diminishing to
5-7 feet by late this afternoon. Seas will hover around or just
above 5 feet tonight. As such, made no changes to the small
craft advisory at this time.
This morning, visibilities near the coast will approach one
mile, but this is expected to be localized, so I declined to
issue a marine dense fog advisory. Nevertheless, expect
visibility reductions early this morning near the coast.
There is a chance of storms through the period but especially
this afternoon and evening. Heavy rain is the main threat from
the storms, but gusty winds and locally higher waves can be
expected near any storm that develops.
Outlook...
Wednesday through Saturday...Seas will remain elevated on the
coastal waters through most if not all of this period. There is
a small chance (less than 30 percent) for tropical storm force
winds primarily for the Delaware Coastal waters.
Rip Currents...
The high surf advisory expired at 5 am, as seas are beginning
to diminish and strong onshore flow has decreased considerably.
A high risk of rip currents exists today, as medium-to-long
period easterly swell continues with wave heights near 5 feet in
the surf zone. Remember to heed the advice of local officials
and stay off the beach if directed to do so. Swimming in these
conditions can be life-threatening.
&&
.TIDES/COASTAL FLOODING...
Coastal Flood Advisory is now in effect for all areas for the
current and upcoming high tide as the tides have continued to
run higher than previously expected. Spotty minor tidal
flooding is expected with the next round of high tide cycles. If
an advisory was needed for this evening's high tide, it would
most likely be the Chesapeake Bay and the tidal Delaware River
and its tributaries in Bucks County, Pennsylvania, and in the
New Jersey counties of Burlington and Mercer.
&&
.EQUIPMENT...
The KDOX radar remains inoperable until further notice. Water
damage to the radar transmitter and product generator is still
being assessed. Due to the unknown extent of the damage, there
is no estimated time for the radar's return to service.
The ASOS (automated surface observing system) at KILG (Wilmington,
DE) took a lightning strike last Friday evening. Looks like
temperature and dew point data have now resumed. Hopefully the
sensors will now remain working. Thanks for the great work techs
in getting the ASOS working again !
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Coastal Flood Advisory until 5 PM EDT this afternoon for
PAZ070-071.
Coastal Flood Advisory until 6 PM EDT this evening for PAZ106.
NJ...High Rip Current Risk until 9 PM EDT this evening for NJZ014-
024>026.
Coastal Flood Advisory until 3 PM EDT this afternoon for
NJZ012>014-016-020>027.
Coastal Flood Advisory until 5 PM EDT this afternoon for
NJZ017-018.
Coastal Flood Advisory until 6 PM EDT this evening for NJZ015-
019.
DE...High Rip Current Risk until 9 PM EDT this evening for DEZ004.
Coastal Flood Advisory until 3 PM EDT this afternoon for
DEZ001>004.
MD...None.
MARINE...Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455.
&&
Synopsis...MPS
Near Term...CMS/Johnson
Short Term...CMS
Long Term...MPS
Aviation...CMS/MPS
Marine...CMS/MPS
Tides/Coastal Flooding...
Equipment...Hazardous Weather Outlook National Weather Service Mount Holly NJ 111 PM EDT Tue Sep 11 2018 MDZ008-012-015-019-020-NJZ001-007>010-PAZ054-055-060>062-101>105- 121715- Cecil-Kent MD-Queen Annes-Talbot-Caroline-Sussex-Warren-Morris- Hunterdon-Somerset-Carbon-Monroe-Berks-Lehigh-Northampton- Western Chester-Eastern Chester-Western Montgomery- Eastern Montgomery-Upper Bucks- 111 PM EDT Tue Sep 11 2018 This Hazardous Weather Outlook is for northeast Maryland, northern New Jersey, northwest New Jersey, east central Pennsylvania, northeast Pennsylvania and southeast Pennsylvania. .DAY ONE...This Afternoon and Tonight. Any thunderstorms that develop this afternoon will be capable of producing heavy rainfall and localized flooding. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Impacts from Hurricane Florence remains possible late in the week. Continue to monitor the latest forecasts from the National Hurricane Center and begin to think of preparations in case Florence has an impact on the region. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. NJZ015-019-PAZ106-121715- Mercer-Northwestern Burlington-Lower Bucks- 111 PM EDT Tue Sep 11 2018 ...COASTAL FLOOD ADVISORY IN EFFECT UNTIL 6 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central New Jersey, southern New Jersey and southeast Pennsylvania. .DAY ONE...This Afternoon and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Coastal Flood Advisory. Any thunderstorms that develop this afternoon will be capable of producing heavy rainfall and localized flooding. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Impacts from Hurricane Florence are possible late in the week. Continue to monitor the latest forecasts from the National Hurricane Center and begin to think of preparations in case Florence has an impact on the region. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. NJZ017-018-PAZ070-071-121715- Gloucester-Camden-Delaware-Philadelphia- 111 PM EDT Tue Sep 11 2018 ...COASTAL FLOOD ADVISORY IN EFFECT UNTIL 5 PM EDT THIS AFTERNOON... This Hazardous Weather Outlook is for southern New Jersey and southeast Pennsylvania. .DAY ONE...This Afternoon and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Coastal Flood Advisory. Any thunderstorms that develop this afternoon will be capable of producing heavy rainfall and localized flooding. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Impacts from Hurricane Florence remains possible late in the week. Continue to monitor the latest forecasts from the National Hurricane Center and begin to think of preparations in case Florence has an impact on the region. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. DEZ001>003-NJZ012-013-016-020>023-027-121715- New Castle-Kent-Inland Sussex-Middlesex-Western Monmouth-Salem-Ocean- Cumberland-Atlantic-Cape May-Southeastern Burlington- 111 PM EDT Tue Sep 11 2018 ...COASTAL FLOOD ADVISORY IN EFFECT UNTIL 3 PM EDT THIS AFTERNOON... This Hazardous Weather Outlook is for central Delaware, northern Delaware, southern Delaware, central New Jersey, northern New Jersey and southern New Jersey. .DAY ONE...This Afternoon and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Coastal Flood Advisory. Any thunderstorms that develop this afternoon will be capable of producing heavy rainfall and localized flooding. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Impacts from Hurricane Florence remains possible late in the week. Continue to monitor the latest forecasts from the National Hurricane Center and begin to think of preparations in case Florence has an impact on the region. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. DEZ004-NJZ014-024>026-121715- Delaware Beaches-Eastern Monmouth-Atlantic Coastal Cape May- Coastal Atlantic-Coastal Ocean- 111 PM EDT Tue Sep 11 2018 ...COASTAL FLOOD ADVISORY IN EFFECT UNTIL 3 PM EDT THIS AFTERNOON... ...HIGH RIP CURRENT RISK IN EFFECT UNTIL 9 PM EDT THIS EVENING... This Hazardous Weather Outlook is for southern Delaware, central New Jersey and southern New Jersey. .DAY ONE...This Afternoon and Tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Coastal Flood Advisory. High Rip Current Risk. Any thunderstorms that develop this afternoon will be capable of producing heavy rainfall and localized flooding. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Impacts from Hurricane Florence are possible late in the week. Continue to monitor the latest forecasts from the National Hurricane Center and begin to think of preparations in case Florence has an impact on the region. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. ANZ430-431-450>455-121715- Delaware Bay waters north of East Point NJ to Slaughter Beach DE- Delaware Bay waters south of East Point NJ to Slaughter Beach DE- Coastal waters from Sandy Hook to Manasquan Inlet NJ out 20 nm- Coastal waters from Manasquan Inlet to Little Egg Inlet NJ out 20 nm- Coastal waters from Little Egg Inlet to Great Egg Inlet NJ out 20 nm- Coastal waters from Great Egg Inlet to Cape May NJ out 20 nm- Coastal waters from Cape May NJ to Cape Henlopen DE out 20 nm- Coastal waters from Cape Henlopen to Fenwick Island DE out 20 nm- 111 PM EDT Tue Sep 11 2018 This Hazardous Weather Outlook is for Atlantic coastal waters and Delaware Bay Waters. .DAY ONE...This Afternoon and Tonight. The probability for widespread hazardous weather is low. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Impacts from Hurricane Florence are possible late in the week. Continue to monitor the latest forecasts from the National Hurricane Center and begin to think of preparations in case Florence has an impact on the region. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
The national radar mosaic for the moment the first event began.
1 flash flood. Local standard time, as filed.
Locally heavy rain resulted in widespread roadway flooding in Milford. Many roads became impassable.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Delaware in 2018Every state in 2018This day in weather historyWarnings in Delaware, September 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 774122.