Tropical Storm Isaias brought high winds, heavy rain, several tornadoes, and coastal flooding to the mid-Atlantic region, becoming the most impactful tropical cyclone to impact most of the region since Sandy in 2012. one in Lehigh County and the other in Montgomery County.
Every event with a place to put it; 11 filed by county or forecast zone are drawn at its center, in a lighter ring. 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.
Tropical Storm Isaias brought high winds, heavy rain, several tornadoes, and coastal flooding to the mid-Atlantic region, becoming the most impactful tropical cyclone to impact most of the region since Sandy in 2012. Flash flooding as a result of heavy rain caused two direct deaths from this event...one in Lehigh County and the other in Montgomery County.
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 Aug 4, 5:59 AM EST, 36 minutes earlier.
Area Forecast Discussion
National Weather Service Mount Holly NJ
659 AM EDT Tue Aug 4 2020
.SYNOPSIS...
Tropical Cyclone Isaias is expected to move north and reach the
Mid Atlantic later Tuesday. Isaias will move toward New England
by Wednesday. High pressure will build in to our north later
this week into this weekend while a weak front lingers to our
south.
&&
.NEAR TERM /THROUGH TONIGHT/...
***Significant Impacts Expected From Isaias***
***Tornado Watch In effect For Delmarva and Parts of Southern NJ***
As of 700 AM, Isaias located over eastern Virginia with showers
and embedded storms streaming north through the area well ahead
of the main system. Lift across the area is being aided by a
strengthening upper jet over western PA / NY as the area is in
the favorable right entrance region. There is also low level
convergence associated with a lingering weak front across the
area. The upshot of all this is that heavy showers with embedded
storms have ramped up already with the threat for flash
flooding and and severe weather already increasing early this
morning. There remains sufficient instability with also very
strong low level shear. For this reason, locally damaging winds
will be possible and even a couple isolated tornadoes given the
strong low level SRH and lowering LCLs. Best chances for this
will be for Delmarva, SE PA, and central and southern NJ but
this threat will spread north through this morning. In fact the
SPC has issued a Tornado Watch covering much of this area
(except SE PA) that is in effect until Noon.
By mid to late morning is when condition deteriorate further as
Isaias quickly advances towards the area. Tropical Cyclone
Isaias will speed quickly northward in response to a strong jet
streak passing through the region. Forecast models and the NHC
remain consistent in tracking the storm right through the heart
of the CWA near the urban corridor. It will also be starting to
undergo extratropical transition as it moves through our region.
The main timeframe of concern for the storm's strong winds,
heaviest rainfall and other associated impacts is mid/late
morning through much of the afternoon before the storm exits by
early this evening.
Multiple hazards with Isaias are expected including, but not
limited to, fresh water flooding, coastal flooding/storm surge,
strong winds and isolated tornadoes. The greatest precipitation
amounts are forecast to fall near and especially N/W of the
urban corridor. 3-6 inches of rain with locally higher amounts
up to 8 inches are expected. This will lead to a high flash
flooding threat, especially for the more urbanized areas and
portions of Berks County that received an excessive amount of
rain Sunday morning. In fact the flooding has the potential to
be widespread and significant. There also continues to be
increasing confidence widespread damaging winds will be an
issue...especially near and to the right of the storms track so
basically from the urban corridor S/E. Again, while the system
will be starting to lose its tropical characteristics, because
of the strong baroclinic zone it will be moving into this won't
allow it to really weaken much. Winds will initially be from the
E/SE then shift to NW behind the system. Sustained winds of 50+
mph are likely along the coast with gusts potentially exceeding
hurricane force (74+ mph). Farther N/W towards the I-95
corridor, widespread gusts of 50 to 60+ mph will be possible.
Importantly, it should be noted that because the storm will be
starting to become extratropical, the strongest winds/gusts over
inland areas could be immediately following the passage of the
storms center this afternoon since there will be better mixing
in this quadrant. And finally, the tornado threat: The threat
for isolated tornadoes is beginning to develop over southern
parts of our region during the predawn hours (as described
above) and this will spread north as we go through the rest of
the night into Tuesday morning. Areas near and S/E of urban
corridor will have the best chance for tornadoes.
The trend is for the storm to move through a bit faster than
previously forecast so expect it should be exiting by the
latter part of this afternoon into this evening. Winds/rain
should abate fairly quickly from south to north as this occurs.
Otherwise, Tuesday night should then finally feature quieter
weather though a secondary front and upper level wave could
trigger a few scattered showers.
&&
.SHORT TERM /WEDNESDAY/...
Quieter weather for Wednesday as high pressure starts to build
in to our north. This will bring a mainly dry day with
seasonable temperatures under partly to mostly sunny skies.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A fairly typical but overall quieter summer pattern is expected
for the long term forecast. The mean upper level trough over the
east will lift out but the mid Atlantic region will remain in a
fairly moist W/SW flow regime around high pressure ridging over
the western Atlantic. This will result in chances for scattered
showers/storms most days that will be mainly diurnally driven
meaning the best chances will be in the afternoon and early
evening. Temperatures will be around average for this time of
year.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY and surrounding areas.
Today... A rapid deterioration in conditions is expected from
south to north soon after 12z. MVFR to IFR conditions are
expected through much of the day in association with Hurricane
Isaias. Areas of torrential rainfall with low vsbys are likely.
Strong and erratic winds are expected with a sharp change in
wind direction expected during the mid afternoon. Gusts may be
briefly higher than shown in the TAFs especially near MIV and
ACY. While confidence is low in exact details and timing,
confidence is high in the overall trend, with hazardous aviation
conditions expected for most of the area.
Tonight... Mainly VFR. Southwest winds 10 to 20 kt diminishing to 5
to 10 kt. Moderate confidence.
Outlook...
Wednesday through Saturday...Mostly VFR. Scattered SHRA/TSRA
possible each afternoon/evening that would result in brief sub-
VFR conditions at a given terminal. Fog may develop during the
overnight. West winds less than 10 kt on Wednesday, then east to
northeast Thursday through Saturday. LGT/VRB at night. Moderate
confidence.
&&
.MARINE...
Today and Tonight... Tropical Storm Warnings are in effect as Isaias
moves north through North Carolina. Isaias will continue to head
north and then northeast and approach the area early this morning.
This morning into afternoon sustained winds of 45 to 55 kts appears
likely with gusts up to Hurricane force expected. Heavy rain, and
isolated waterspouts, this morning into early afternoon will give
way to a gradual improving of conditions later this afternoon. Seas
will also build to between 12 and 18 feet over the Atlantic coastal
waters. A slow decrease in seas down towards 5 feet can be expected
by Wednesday morning.
Outlook...
Wednesday morning...Seas may linger near 5 feet on the New Jersey
coastal waters but should subside below advisory criteria by midday.
Wednesday afternoon through Saturday...Sub-advisory winds/seas
expected through the period. Chances of showers/storms through the
period, especially in the afternoon/evening hours.
Rip Currents...
On Tuesday, impacts from Isaias will increase the rip-current risk
level to high. In addition, high surf is expected. A rip
current risk statement and high surf advisory are in effect for
this period, so in conclusion Tuesday will not be a good day to
be at the beach.
The rip current risk will likely remain elevated on Wednesday.
&&
.HYDROLOGY...
Hydro concerns continue early this morning as showers/storms continue
ahead of Isaias. Any of these will be capable of producing heavy
rain with at least localized flash flooding possible. The heaviest,
steadiest rain with the storm will arrive this morning from
south to north with more widespread flash flooding becoming a
big concern during this time. Most susecptible areas will be
near and N/W of the I-95 corridor especially since places such
as in Berks County have received so much rainfall recently. With
Isaias, 3 to 6 inches of rain, with locally higher amounts are
expected. Flooding could be widespread and significant.
In addition to flash flooding, river flooding is also expected. But
with a more consolidated area of rainfall across PA, the threat
across NJ including the Passaic and Raritan basins has lessened. The
latest MARFC forecast still has about 15 forecast points above
Action Stage and 6 at or above Flood Stage, including, Philadelphia,
Norristown, and Pottstown on the Schuylkill, Graterford on Perkiomen
Creek, Langhorne on Neshaminy Creek, and Chadds Ford and Wilmington
on the Brandywine. The latest forecast has these points cresting
later today or tonight. With such a large swath of precipitation
expected along and west of the I95 corridor, most basins in this
area will see at least some threat. That said, the Delaware River is
expected to remain within its banks.
&&
.TIDES/COASTAL FLOODING...
The coastal flooding impacts from Isaias remain very uncertain at
this time. Models notoriously handle fast-moving, intense cyclones
poorly in our area, as the short duration of onshore flow competes
with the strength of the winds. These competing impacts and
sensitivities are not well understood from a modeling standpoint,
leading to rather large spread in the model guidance.
Coastal flooding impacts are expected across the area today, with
four different regions we will be monitoring. The first, and
potentially most significant, is for the eastern shore of Chesapeake
Bay, where surge will likely move northward during the day. What is
unclear, however, is the strength of this surge. Model guidance is
particularly poor for these areas, and the output the past couple of
days seems unrealistically low. However, the extent of impacts
remains quite unclear. At this point, there is potential for
moderate flooding, which requires continuation of the coastal flood
warning. However, it is possible impacts will be less
significant/widespread. We will likely not have a better idea of
impacts until after daybreak, when gauges in lower Chesapeake Bay
begin to respond.
The second area is Delaware Bay. The real question here will be the
timing of the surge relative to the astronomical high tide.
With guidance trending a little faster with the surge, the timing
looks a little less favorable for coincidence of peak surge and
astronomical high tide for the Delaware Bay sites.
Nevertheless, the strength of southeast winds in advance of Isaias
may compensate much more readily than models suggest. A coastal
flood advisory has been issued here for the entire day given the
uncertainty of peak surge timing.
The third area is the tidal Delaware River. Here, confidence is
increasing that minor flooding will occur during the afternoon, as
predecessor southeast winds will likely combine with freshwater
runoff to lead to a period of tidal flooding from early afternoon to
early evening. As with Delaware Bay, confidence is not particularly
high on exact timing of flooding, so have issued a coastal flood
advisory for a broader period of time than normal (11 am to 8 pm).
The fourth area is the Atlantic coast. As with Delaware Bay, timing
of the strongest surge appears to occur between astronomical high
tides. However, the strength of onshore flow and exacerbating
behavior of wave runup will likely produce areas of flooding. Of
particular concern is back bays that are susceptible to southeast
flow, which can act to trap water. Barnegat Bay and Little Assawoman
Bay are particularly susceptible in these regimes, and these areas
may experience more widespread/significant flooding. Confidence is
pretty low in general for the coast, but given the very strong
onshore flow expected today, suspect at least some impacts in the
especially vulnerable spots are likely.
&&
.EQUIPMENT...
The NOAA Weather Radio All-Hazards broadcast from Hibernia Park
Pennsylvania (Station WNG-704) remains off the air.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...Flash Flood Watch through this evening for PAZ054-055-060>062-
070-071-101>106.
Tropical Storm Warning for PAZ070-071-101>106.
Coastal Flood Advisory from 11 AM this morning to 8 PM EDT
this evening for PAZ070-071-106.
NJ...Flash Flood Watch through this evening for NJZ001-007>010-
012>027.
Tropical Storm Warning for NJZ001-007>010-012>027.
Coastal Flood Advisory until 8 PM EDT this evening for NJZ016-
021-023-024.
High Rip Current Risk through this evening for NJZ014-024>026.
High Surf Advisory until midnight EDT tonight for NJZ014-
024>026.
Coastal Flood Advisory from 11 AM this morning to 2 AM EDT
Wednesday for NJZ012>014-020-022-025>027.
Coastal Flood Advisory from 11 AM this morning to 8 PM EDT
this evening for NJZ017>019.
DE...Flash Flood Watch through this evening for DEZ001>004.
Tropical Storm Warning for DEZ001>004.
Coastal Flood Advisory until 8 PM EDT this evening for
DEZ001>004.
High Rip Current Risk through this evening for DEZ004.
High Surf Advisory until midnight EDT tonight for DEZ004.
MD...Flash Flood Watch through this evening for MDZ008-012-015-019-
020.
Tropical Storm Warning for MDZ008-012-015-019-020.
Coastal Flood Warning from 11 AM this morning to 6 AM EDT
Wednesday for MDZ008-012-015-019-020.
MARINE...Tropical Storm Warning for ANZ430-431-450>455.
&&
Synopsis...Fitzsimmons
Near Term...Fitzsimmons
Short Term...Fitzsimmons
Long Term...Fitzsimmons/MPS
Aviation...O'Brien
Marine...CMS
Hydrology...WFO PHI
Tides/Coastal Flooding...WFO PHI
Equipment...WFO PHIHazardous Weather Outlook National Weather Service Mount Holly NJ 725 AM EDT Tue Aug 4 2020 PAZ054-055-060>062-051200- Carbon-Monroe-Berks-Lehigh-Northampton- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... This Hazardous Weather Outlook is for east central Pennsylvania and northeast Pennsylvania. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. There is a low probability for widespread hazardous weather. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. MDZ008-012-015-019-020-051200- Cecil-Kent MD-Queen Annes-Talbot-Caroline- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 415 IN EFFECT UNTIL NOON EDT TODAY... ...TROPICAL STORM WARNING IN EFFECT... ...COASTAL FLOOD WARNING IN EFFECT FROM 11 AM THIS MORNING TO 6 AM EDT WEDNESDAY... This Hazardous Weather Outlook is for northeast Maryland. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. Coastal Flood Warning. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. NJZ001-007>010-015-PAZ101>105-051200- Sussex-Warren-Morris-Hunterdon-Somerset-Mercer-Western Chester- Eastern Chester-Western Montgomery-Eastern Montgomery-Upper Bucks- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 416 IN EFFECT UNTIL 4 PM EDT THIS AFTERNOON... ...TROPICAL STORM WARNING IN EFFECT... This Hazardous Weather Outlook is for central New Jersey, northern New Jersey, northwest New Jersey and southeast Pennsylvania. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. NJZ017>019-PAZ070-071-106-051200- Gloucester-Camden-Northwestern Burlington-Delaware-Philadelphia- Lower Bucks- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 416 IN EFFECT UNTIL 4 PM EDT THIS AFTERNOON... ...TROPICAL STORM WARNING IN EFFECT... ...COASTAL FLOOD ADVISORY IN EFFECT FROM 11 AM THIS MORNING TO 8 PM EDT THIS EVENING... This Hazardous Weather Outlook is for southern New Jersey and southeast Pennsylvania. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. Coastal Flood Advisory. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. DEZ001>003-NJZ016-021-023-051200- New Castle-Kent-Inland Sussex-Salem-Cumberland-Cape May- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 415 IN EFFECT UNTIL NOON EDT TODAY... ...TROPICAL STORM WARNING IN EFFECT... ...COASTAL FLOOD ADVISORY IN EFFECT UNTIL 8 PM EDT THIS EVENING... This Hazardous Weather Outlook is for central Delaware, northern Delaware, southern Delaware and southern New Jersey. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. Coastal Flood Advisory. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. NJZ012-013-020-022-027-051200- Middlesex-Western Monmouth-Ocean-Atlantic-Southeastern Burlington- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 416 IN EFFECT UNTIL 4 PM EDT THIS AFTERNOON... ...TROPICAL STORM WARNING IN EFFECT... ...COASTAL FLOOD ADVISORY IN EFFECT FROM 11 AM THIS MORNING TO 2 AM EDT WEDNESDAY... This Hazardous Weather Outlook is for central New Jersey, northern New Jersey and southern New Jersey. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. Coastal Flood Advisory. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. NJZ014-025-026-051200- Eastern Monmouth-Coastal Atlantic-Coastal Ocean- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 416 IN EFFECT UNTIL 4 PM EDT THIS AFTERNOON... ...TROPICAL STORM WARNING IN EFFECT... ...HIGH SURF ADVISORY IN EFFECT UNTIL MIDNIGHT EDT TONIGHT... ...HIGH RIP CURRENT RISK IN EFFECT THROUGH THIS EVENING... ...COASTAL FLOOD ADVISORY IN EFFECT FROM 11 AM THIS MORNING TO 2 AM EDT WEDNESDAY... This Hazardous Weather Outlook is for central New Jersey and southern New Jersey. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. High Rip Current Risk. High Surf Advisory. Coastal Flood Advisory. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. DEZ004-NJZ024-051200- Delaware Beaches-Atlantic Coastal Cape May- 725 AM EDT Tue Aug 4 2020 ...FLASH FLOOD WATCH IN EFFECT THROUGH THIS EVENING... ...TORNADO WATCH 415 IN EFFECT UNTIL NOON EDT TODAY... ...TROPICAL STORM WARNING IN EFFECT... ...COASTAL FLOOD ADVISORY IN EFFECT UNTIL 8 PM EDT THIS EVENING... ...HIGH SURF ADVISORY IN EFFECT UNTIL MIDNIGHT EDT TONIGHT... ...HIGH RIP CURRENT RISK IN EFFECT THROUGH THIS EVENING... This Hazardous Weather Outlook is for southern Delaware and southern New Jersey. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Flash Flood Watch. Tornado Watch. Tropical Storm Warning. Coastal Flood Advisory. High Rip Current Risk. High Surf Advisory. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. ANZ430-431-453>455-051200- 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 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- 725 AM EDT Tue Aug 4 2020 ...TORNADO WATCH 415 IN EFFECT UNTIL NOON EDT TODAY... ...TROPICAL STORM WARNING IN EFFECT... This Hazardous Weather Outlook is for Atlantic coastal waters and Delaware Bay Waters. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tornado Watch. Tropical Storm Warning. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures. ANZ450>452-051200- 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- 725 AM EDT Tue Aug 4 2020 ...TORNADO WATCH 416 IN EFFECT UNTIL 4 PM EDT THIS AFTERNOON... ...TROPICAL STORM WARNING IN EFFECT... This Hazardous Weather Outlook is for Atlantic coastal waters. .DAY ONE...Today and tonight. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tornado Watch. Tropical Storm Warning. .DAYS TWO THROUGH SEVEN...Wednesday through Monday. Please listen to NOAA Weather Radio or go to weather.gov on the Internet for more information about the following hazards. Tropical Storm Warning. .SPOTTER INFORMATION STATEMENT... Weather spotters are encouraged to report significant weather conditions according to standard operating procedures.
The Philadelphia radar (KDIX), 79 km away, was scanning. The volume nearest the first event began at 11:37 UTC.
62 flash flood, 10 tropical storm, 4 tornado, 1 flood, 1 coastal flood. Local standard time, as filed.
Darby Creek Road was closed near Lawrence Road in Haverford Township due to flooding.
Widespread roadway flooding in Radnor Township.
Multiple water rescues in Upper Merion Township.
Multiple water rescues in Norristown.
Major flooding occurred along Cobbs Creek in Philadelphia.
Major flooding occurred along Chester Creek in the Chester area.
Major flooding occurred on the East Branch of the Perkiomen Creek in the Dublin and Perkasie area.
A wind gust of 65 mph was measured by a DEOS gauge at White Clay Creek in West Grove, and sustained tropical storm force winds likely occurred. A number of reports of downed trees and wires were received.
Multiple reports of downed trees and wires were received, and surrounding observations suggest sustained tropical storm force winds likely occurred.
Few reliable anemometers exist in Delaware County and no sustained tropical storm force winds were measured. However, observations from surrounding areas along with multiple reports of downed trees and power lines suggest tropical storm conditions very likely occurred.
Friedensville Road was closed near Meadows Road along the Bethlehem and Lower Saucon Township line due to flooding.
Moderate flooding occurred along Crum Creek near Newtown Square.
A sustained wind of 40 mph with gusts to 49 mph was measured at Philadelphia Northeast Airport (KPNE). A number of reports of downed trees and power lines were received in the county, with locally enhanced damage due to a tornado over Northeast Philadelphia.
Numerous reports of downed trees and wires were received in Lower Bucks, including locally enhanced damage near Doylestown due to a tornado. A wind gust of 51 mph was measured near the Bucks/Burlington County border, and reports suggest it is very likely that sustained tropical storm force winds occurred.
A trained spotter in Eagleville measured sustained winds up to 42 mph. Several reports of downed trees and power lines were received.
Several reports of downed trees and wires were received. Sustained tropical storm force winds were measured both immediately east and west of the area indicating they likely occurred here as well.
PA Route 841 was closed near Lewisville Road in Elk Township due to flooding.
Observations from surrounding areas as well as reports of downed trees and power lines suggest tropical storm force winds likely occurred.
South Bryn Mawr Avenue was closed near Mill Road in Radnor Township due to flooding.
South University Avenue was closed at South 38th Street in Philadelphia due to flooding.
Blueball Avenue was closed near West 10th Street in Marcus Hook due to flooding.
Major flooding occurred along the Wissahickon Creek in Philadelphia.
Moderate flooding occurred along the Frankford Creek in Philadelphia.
An EF0 tornado occurred in Worcester Township in Montgomery |County, Pennsylvania as Tropical Storm Isaias moved northward |along the East Coast of the United States. With southeastern |Pennsylvania being in the northeastward, right front quadrant, the|tornado and parent storm moved in an unusual northwestward |trajectory ahead of the main center of the tropical storm. An area|of circulation tightened in a strong cell within a rainband in |southeastern Montgomery County. As this circulation tightened, a |brief tornado formed near the intersection of Brindle Court and |Township Line Road in Worcester Township, where a few small trees |were downed in a small residential subdivision. From here, the |tornado continued its northwestward trajectory through the |township, downing trees along Potshop Road. The circulation may |have lifted with the path being somewhat discontinuous. A somewhat|denser area of trees were downed as the tornado moved across |Valley Forge Road and northwestward along Heebner Road. Several |tree tops were sheared off in addition to several utility poles |being pushed over along Heebner Road near the intersection of |Shefley Lane. The tornado continued northwest from here, |eventually downing several hardwood trees along Hollow Road. One |tree brought down several utility lines as it fell. From here, the|tornado lifted with only a few other trees being downed a little |ways from Hollow Road in a small wooded area.
PA Route 926 was closed near PA Route 10 in Upper Oxford Township due to flooding.
Major flooding occurred along Ridley Creek near Media.
A tornado touched down just east of the Philadelphia Mills Mall as it moved in a northwesterly direction. The initial touchdown occurred in Bucks County, very near the Philadelphia County border. Uprooted trees were found near the area of Kings Ave and Paradise Ave. The tornado then quickly approached the county line at Pocquessing Creek.
After crossing into Philadelphia County, the tornado continued moving northwest through the Philadelphia Mills Mall and then to Knights Road and Medford Road toward Dunks Ferry Road. Three exhaust |systems and 6 RTU systems were blown off the roof in less than 15 |seconds at the former Walmart Store currently undergoing |reconstruction, and numerous trees, some close to 100 years old, |were snapped or blown over along Knights Road, Medford Road, and |Dunks Ferry Road. Roofs, siding, and awnings were blown off many |homes in the area. A few cars were also tossed or turned over as |the storm moved through. The estimated wind speed in this area was|100 mph, equivalent to EF1 on the Enhanced Fujita scale. The tornado may have briefly lifted as it continued northwestward and prepared to cross into Bucks County for a second time.
Major flooding occurred along the Wissahickon Creek in the Fort Washington area.
After crossing back into Bucks County, the tornado, which may have lifted for a time, caused additional damage in the Southampton area of Bucks County. Numerous trees were snapped |in this area as well, with many homes and cars damaged due to |falling trees and tree limbs. The Sycamore Drive and Harding Roads|areas were hardest hit. The estimated wind speed in this area was|90 mph, equivalent to an EF1 on the Enhanced Fujita scale.| |Current evidence again suggests the tornado lifted one more time |as the parent circulation traveled to the Doylestown area, where |it touched down one final time near the Central Bucks West High |School. Here bleachers on the visitor’s side of the athletic |field were picked up and tossed before the vortex moved on to the |Doylestown Hospital complex where at least six automobiles were |tossed some distance, and where substantial damage occurred to the|Children’s Village Day Care center with no serious injuries |reported. Numerous trees were felled in and around the hospital |center, and several metal lamp posts were bent from the wind. The |estimated wind speed in this area was 115 mph, equivalent to a |low-end EF2 on the Enhanced Fujita scale. The tornado then |continued moving in a northwesterly direction, snapping and |falling trees, as well as causing damage to homes and other |properties, especially along and near Sandy Ridge Road, Jefferson |Avenue, and Lower State Road, before lifting along Ferry Road near|the Peace Valley Reservoir. The estimated wind speed in this area|was 100 mph, equivalent to an EF1 on the Enhanced Fujita scale.
Several water rescues took place in Skippack Township.
PA Route 320 was closed at Old Marple Road in Marple Township due to flooding.
Multiple reports of 40 to 50 mph sustained winds were received including at Lehigh Valley International Airport (KABE). This led to multiple reports of downed trees and power lines.
A 5-year-old girl with autism was swept away by flood waters running through a tributary of Towamencin Creek after wandering away from her nearby family home. Rescuers found the victim's body adjacent to the creek in Fischer's Park after a 22-hour search.
Moderate flooding occurred along Valley Creek in the Valley Forge area.
Major flooding occurred along the Perkiomen Creek in the East Greenville area.
Birmingham Road was closed near Riflery Drive in East Bradford Township due to flooding.
Concord Road was closed near Interstate 95 in Chester Township due to flooding.
Major flooding occurred along the Monocacy Creek in the Bethlehem area.
US Route 1 was closed near Valleybrook Road in Chester Heights due to flooding.
Interstate 76 was closed at the US Route 202 interchange in King of Prussia due to flooding. Sections of US 202 were also closed due to flooding.
Haverford Road was closed at Karakung Drive in Ardmore due to flooding.
A car driven by a 44-year-old woman was swept away by flood waters along the 6300 block of North Main Street in Upper Saucon Township near a bridge that passes over Laurel Run. The victim was pronounced dead later in the day after the waters receded.
Swinehart Road was closed near Beaver Creek Road in West Brandywine Township due to flooding.
Moderate flooding occurred along the West Branch of the Perkiomen Creek upstream from the Green Lane Reservoir.
Minor flooding occurred along the Little Neshaminy Creek in the Hartsville area.
Major flooding occurred on the East Branch of the Perkiomen Creek near Schwenksville.
Minor flooding occurred along the Red Clay Creek in the Kennett Square area.
PA Route 363 was closed at Audubon Road in Audubon due to flooding.
Minor flooding occurred along the West Branch of the Brandywine Creek in the Modena area.
Major flooding occurred on the East Branch of the Brandywine Creek, downstream from Downingtown.
US Route 30 was closed near the Lancaster Avenue interchange in East Caln Township due to flooding.
Several roads in Exton were closed due to flooding, including sections of Business US Route 30 and PA Route 100.
Major flooding occurred along the White Clay Creek in the Strickersville area.
North Ship Road was closed at Newcomen Road in Uwchlan Township due to flooding.
Minor flooding occurred along French Creek in Phoenixville.
Minor flooding occurred along the Pennypack Creek in Philadelphia.
Zucksville Road was under water near Bushkill Drive in Forks Township.
Tatamy Road was under water at Friendenstahl Avenue near Nazareth.
PA Route 23 was closed at PA Route 100 in South Coventry Township due to flooding.
Major flooding occurred along the Perkiomen Creek in the Graterford area.
A CWOP site in Palmer measured a wind gust of 53 mph. A number of reports of downed trees and power lines were received, indicating sustained tropical storm force winds likely occurred.
Widespread roadway flooding in Bethlehem Township, including Easton Avenue and Farmersville Road.
Several water rescues took place in North Coventry Township.
PA Route 100 was closed at Swamp Creek Road in Colebrookdale Township due to flooding.
Major flooding occurred along the Little Lehigh Creek in the Allentown area.
Cherry Valley Road was closed near Goodale Road in Hamilton Township due to flooding.
Sections of PA Route 12 in Muhlenberg Township were closed due to flooding.
Several roads were closed in Palmer Township and Forks Township, including Tatamy Road, Bushkill Park Drive and Arndt Road.
PA Route 309 was closed at West Saucon Valley Road in Upper Saucon Township due to flooding.
East Lawn Road was closed in Eastlawn Gardens due to flooding.
Several roads were closed due to flooding in Bethlehem.
Interstate 78 was closed at the US Route 22 interchange in Upper Macungie Township due to flooding.
Brookside Road was closed at Buckeye Road in Lower Macungie Township due to flooding.
Grouse Drive was closed near Whitetail Deer Drive in Moore Township due to flooding.
Widespread roadway flooding in Lehigh Township.
Moderate flooding occurred along the Neshaminy Creek in the Penns Park and Rushland area.
Moderate coastal flooding occurred. There was roadway flooding in some of the tidal areas of lower Bucks County along the Delaware River and its tidal tributaries.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Flash Flood, Montgomery | 2020-08-04 | 5 | Female | Outside/Open Areas | Direct |
| Flash Flood, Lehigh | 2020-08-04 | 44 | Female | Unknown | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2020Every state in 2020This day in weather historyThe tornado archive for Pennsylvania, 2020Warnings in Pennsylvania, August 2020The 2020 hurricane season
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: 899403, 899402, 899401, 899400, 899980, 899828, 899830, 907707, 907732, 907742, 899410, 899826, 907743, 907745, 907747, 907749, 899746, 907750, 899759, 899760, 899748, 899981, 899982, 904093, 899751, 899827, 904094, 926364, 899831, 926365, 899411, 899761, 907755, 928259, 899811, 899978, 899750, 899752, 899829, 899753, and more.