Successive waves of thunderstorms with very heavy rain associated with the remnants of Hurricane Isaac overnight on the 3rd into the evening of the 4th produced pockets of flash flooding in Eastern Pennsylvania. By far the worst flash flooding occurred in Monroe County where Doppler Radar storm total estimates exceeded 6 inches.
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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.
Successive waves of thunderstorms with very heavy rain associated with the remnants of Hurricane Isaac overnight on the 3rd into the evening of the 4th produced pockets of flash flooding in Eastern Pennsylvania. By far the worst flash flooding occurred in Monroe County where Doppler Radar storm total estimates exceeded 6 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 4, 3:30 AM EST, 15 minutes earlier.
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 430 AM EDT TUE SEP 4 2012 .SYNOPSIS... A WARM FRONT EXTENDED EASTWARD FROM LOW PRESSURE IN THE OHIO RIVER VALLEY TO MARYLAND AND DELAWARE AND THE ADJACENT COASTAL WATERS EARLY THIS MORNING. THE LOW IS FORECAST TO DRIFT TO THE NORTHEAST AND IT SHOULD PULL THE FRONT SLOWLY TO THE NORTH DURING TODAY AND TONIGHT. AS THE LOW REACHES THE VICINITY OF MAINE AND CANADA'S MARITIME PROVINCES ON WEDNESDAY NIGHT, IT IS EXPECTED TO PULL A TRAILING FRONTAL BOUNDARY THROUGH OUR REGION. A COLD FRONT FROM THE NORTHWEST IS FORECAST TO ARRIVE EARLY ON FRIDAY FOLLOWED BY WEAK HIGH PRESSURE. SLOW MOVING LOW PRESSURE AND A FRONTAL BOUNDARY FROM THE WEST MAY INFLUENCE OUR REGION OVER THE WEEKEND AND INTO MONDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... CNVTV ACTVTY DEFINITELY INCREASED DURG LATE EVE INTO THE OVERNIGHT HOURS. IT HAS BEEN ORIENTED IN A MAINLY W-E BAND ACROSS SRN AND SE PA INTO SRN NJ. NOT EXACTLY CLEAR WHAT IS DRIVING THIS LATEST ROUND EXCEPT THAT THE AMS CONTS TO BE VERY MOIST AND SMWHT UNSTABLE... ESPCLY ACRS THE CNTRL AND SRN PARTS OF OUR FCST AREA. LATEST RAP MODEL DOES SHOW GOOD UVV OVER THE AREA. STORMS ARE PRODUCING LCLLY HVY RAIN AND SOME FLOODING...BUT FORTUNATELY THE WORST OF IT SEEMS TO BE OVER SMWHT SPARSELY POPULATED AREAS IN SRN NJ. CNVTN IS EXPECTED TO CONT FOR A FEW MORE HRS WITH PERHAPS A SLOW NWD SHIFT. OTRW HAVE GENLY MAINTAINED THE CURRENT FCST WITH LIKELY POPS FOR MOST OF THE AREA THROUGH TUESDAY. ELY WINDS EARLY THIS MORN SHOULD INCR AND BECOME SLY BY AFTN. MAX TEMPS ARE A BLEND OF MAV/MET GUIDANCE. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... LOW PRES OVER ERN OH IS FCST TO TRACK NEWD INTO UPSTATE NY DURG THIS PD...WITH A CDFNT TRAILING SWWD. HWVR OUR FCST AREA WILL REMAIN IN THE MOIST TROPICAL AMS AHD OF THE FNT AND THUS THE POTENTIAL FOR HEAVY SHOWERS AND TSTMS WILL CONT. THERE SHOULD BE ENOUGH OF A PRES GRADIENT TO MAINTAIN LIGHT SLY WINDS OVERNIGHT. MIN TEMPS SHOULD BE SIMILAR TO EARLY THIS MORNING. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... ON WEDNESDAY MORNING, THE AXIS OF DEEP MOISTURE WILL EXTEND THROUGH OUR FORECAST AREA. PRECIPITABLE WATER VALUES SHOULD BE IN EXCESS OF 2 INCHES AT MOST LOCATIONS. A LOW LEVEL JET IS EXPECTED TO EXTEND FROM THE CAROLINAS TO NEW ENGLAND AT THAT TIME. BOTH FEATURES ARE ANTICIPATED TO DRIFT EASTWARD ON WEDNESDAY. HOWEVER, THE THREAT OF HEAVY RAIN WILL REMAIN THROUGH MUCH OF THE DAY, DECREASING SLOWLY FROM WEST TO EAST. AS A RESULT, THE FLASH FLOOD WATCH WILL BE EXTENDED INTO WEDNESDAY EVENING. A MID LEVEL SHORT WAVE OVER THE DAKOTAS EARLY THIS MORNING IS FORECAST TO WORK ITS WAY TO THE EAST. THE FEATURE IS EXPECTED TO PASS OVERHEAD FROM WEDNESDAY AFTERNOON INTO WEDNESDAY EVENING. IT WILL HELP TO KICK THE DEEP MOISTURE OFF THE COAST ON WEDNESDAY NIGHT, FURTHER DECREASING THE POTENTIAL FOR HEAVY RAIN IN OUR REGION. FOR THURSDAY, THERE WILL REMAIN SOME INSTABILITY IN OUR REGION AS ANOTHER MID LEVEL SHORT WAVE APPROACHES FROM THE NORTHWEST. AS A RESULT, WE WILL KEEP THE MENTION OF A CHANCE OF SHOWERS AND THUNDERSTORMS. THE SHORT WAVE IS EXPECTED TO PASS OVERHEAD ON THURSDAY AFTERNOON. A SURFACE COLD FRONT ASSOCIATED WITH THE FEATURE SHOULD ARRIVE FOR LATE THURSDAY NIGHT AND EARLY FRIDAY. WEAK HIGH PRESSURE AND DRY AIR ARE EXPECTED TO FOLLOW FOR FRIDAY INTO FRIDAY NIGHT. A MID LEVEL TROUGH IS ANTICIPATED TO DIG OVER THE EASTERN HALF OF THE COUNTRY FOR THE WEEKEND AND INTO THE EARLY PART OF THE NEW WEEK. CONDITIONS ARE FORECAST TO BECOME UNSETTLED AGAIN DURING THAT PERIOD WITH A CHANCE OF PRECIPITATION. TEMPERATURES MAY BE SLIGHTLY ABOVE NORMAL FOR WEDNESDAY THROUGH FRIDAY AND NEAR NORMAL FOR SATURDAY THROUGH MONDAY. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. IFR CIGS SHOULD PREVAIL OVERNIGHT BUT VSBYS WILL REMAIN HIGH... EXCEPT IN HEAVY SHOWERS OR ISOLD TSTMS. THESE CONDS WILL PERSIST INTO TUE MORNING BUT SHOULD IMPROVE SMWHAT BY MID MORNING. MAINLY VFR CONDS ARE EXPECTED BY TUE AFTN. HWVR...SHWRS/TSTMS FROM TIME TO TIME WILL RESULT IN PERIODS OF MVFR TO IFR CIGS/VSBYS BUT IN GENERAL THESE SHOULD NOT LAST VERY LONG AT ANY GIVEN SITE. TAFS WILL BE UPDATED BASED ON SHORT-TERM FCSTS WITH AS MUCH LEAD TIME AS POSSIBLE. WINDS OVERNIGHT WILL BE LIGHT ELY BUT ARE FCST TO BECOME SLY BY MID DAY TUE AND BECOME A LITTLE STRONGER. OUTLOOK... WEDNESDAY...SHOWERS LIKELY WITH A CHANCE OF THUNDERSTORMS. THERE IS THE POTENTIAL FOR PERIODS OF MODERATE TO HEAVY RAIN ACCOMPANIED BY MVFR OR IFR CONDITIONS. MVFR OR IFR CONDITIONS ARE ALSO POSSIBLE IN MORNING FOG, HAZE AND LOW CLOUDS. WEDNESDAY NIGHT AND THURSDAY...MAINLY VFR WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. MVFR OR IFR CONDITIONS ARE ALSO POSSIBLE IN LATE NIGHT AND EARLY MORNING FOG, HAZE AND LOW CLOUDS. THURSDAY NIGHT THROUGH FRIDAY NIGHT...MAINLY VFR. SATURDAY...MAINLY VFR WITH A CHANCE OF SHOWERS AND THUNDERSTORMS. && .MARINE... SELY WINDS OVER THE COASTAL WATERS WILL BECOME MORE SLY TODAY AS THE FNTL BNDRY ACROSS DELMARVA GRDLY LIFTS NWD. WINDS AND SEAS ARE EXPECTED TO INCREASE A BIT TONIGHT AND COULD APPROACH SCA CONDS AT TIMES. SITN APPEARS MARGINAL HWVR SO WILL HOLD OFF ISSUING ANY ADVISORIES FOR NOW. SCATTERED SHOWER AND TSTM ACTVTY WILL CONT WITH LCLLY POOR VSBYS AND HIGHER WINDS NEAR TSTMS. OUTLOOK... A WARM FRONT IS FORECAST TO LIFT SLOWLY OVER THE COASTAL WATERS OF DELAWARE AND NEW JERSEY DURING TODAY WITH ANOTHER FRONTAL BOUNDARY ARRIVING FROM THE WEST ON WEDNESDAY NIGHT. A COLD FRONT FROM THE NORTHWEST IS ANTICIPATED FOR EARLY FRIDAY. WIND SPEEDS AND GUSTS SHOULD REMAIN LESS THAN 25 KNOTS THROUGH THE PERIOD. FROM WEDNESDAY THROUGH SATURDAY, LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTAL WATERS OF DELAWARE AND NEW JERSEY. WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD BE 5 FEET OR GREATER DURING THAT PERIOD WITH A SMALL CRAFT ADVISORY LIKELY. && .RIP CURRENTS... LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTS OF DELAWARE AND NEW JERSEY INTO AT LEAST THE EARLY PART OF NEXT WEEK. AS A RESULT, A PROLONGED PERIOD WITH A MODERATE TO HIGH RISK OF RIP CURRENTS IS ANTICIPATED. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR PAZ067>071. NJ...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR NJZ015>019. DE...FLASH FLOOD WATCH THROUGH WEDNESDAY EVENING FOR DEZ001. MD...NONE. MARINE...NONE. && SYNOPSIS...IOVINO NEAR TERM...AMC SHORT TERM...AMC LONG TERM...IOVINO AVIATION...AMC/IOVINO MARINE...AMC/IOVINO RIP CURRENTS...IOVINO
HAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE MOUNT HOLLY NJ 435 AM EDT TUE SEP 4 2012 DEZ002-003-MDZ008-012-015-019-020-NJZ001-007>010-012-013-020>023-027- PAZ054-055-060>062-050845- KENT-INLAND SUSSEX-CECIL-KENT MD-QUEEN ANNES-TALBOT-CAROLINE-SUSSEX- WARREN-MORRIS-HUNTERDON-SOMERSET-MIDDLESEX-WESTERN MONMOUTH-OCEAN- CUMBERLAND-ATLANTIC-CAPE MAY-SOUTHEASTERN BURLINGTON-CARBON-MONROE- BERKS-LEHIGH-NORTHAMPTON- 435 AM EDT TUE SEP 4 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL DELAWARE...SOUTHERN DELAWARE...NORTHEAST MARYLAND...CENTRAL NEW JERSEY...NORTHERN NEW JERSEY...NORTHWEST NEW JERSEY...SOUTHERN NEW JERSEY...EAST CENTRAL PENNSYLVANIA AND NORTHEAST PENNSYLVANIA. .DAY ONE...TODAY AND TONIGHT. LOCALLY HEAVY RAINFALL AND SOME FLOODING IS POSSIBLE. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY. LOCALLY HEAVY RAINFALL AND SOME FLOODING IS POSSIBLE ON WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. DEZ001-NJZ015>019-PAZ067>071-050845- NEW CASTLE-MERCER-SALEM-GLOUCESTER-CAMDEN-NORTHWESTERN BURLINGTON- CHESTER-MONTGOMERY-BUCKS-DELAWARE-PHILADELPHIA- 435 AM EDT TUE SEP 4 2012 ...FLASH FLOOD WATCH IN EFFECT THROUGH WEDNESDAY EVENING... THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHERN DELAWARE...CENTRAL NEW JERSEY...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. .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. FLASH FLOOD WATCH. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. DEZ004-NJZ014-024>026-050845- DELAWARE BEACHES-EASTERN MONMOUTH-ATLANTIC COASTAL CAPE MAY- COASTAL ATLANTIC-COASTAL OCEAN- 435 AM EDT TUE SEP 4 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHERN DELAWARE...CENTRAL NEW JERSEY AND SOUTHERN NEW JERSEY. .DAY ONE...TODAY AND TONIGHT. THERE IS A MODERATE RISK OF RIP CURRENTS. LOCALLY HEAVY RAINFALL AND SOME FLOODING IS POSSIBLE. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY. LONG PERIOD SWELLS FROM DISTANT TROPICAL SYSTEM LESLIE ARE FORECAST TO AFFECT THE COASTS OF DELAWARE AND NEW JERSEY INTO AT LEAST THE EARLY PART OF NEXT WEEK. AS A RESULT, A PROLONGED PERIOD WITH A MODERATE TO HIGH RISK OF RIP CURRENTS IS ANTICIPATED. LOCALLY HEAVY RAINFALL AND SOME FLOODING IS POSSIBLE ON WEDNESDAY. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME. ANZ430-431-450>455-050845- 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- 435 AM EDT TUE SEP 4 2012 THIS HAZARDOUS WEATHER OUTLOOK IS FOR ATLANTIC COASTAL WATERS AND DELAWARE BAY WATERS. .DAY ONE...TODAY AND TONIGHT. THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY. THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW. .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.
The Philadelphia radar (KDIX), 62 km away, was scanning. The volume nearest the first event began at 08:44 UTC.
5 flash flood, 2 flood. Local standard time, as filed.
Thunderstorms with very heavy downpours caused flash flooding along the Southampton Creek in Upper Moreland Township. Flooding from the creek was reported around Byberry and Pioneer Roads. Storm totals included 2.22 in Williow Grove and 2.12 inches in Jenkintown.
Runoff from heavy rain that fell in Montgomery County earlier in the day caused flooding along the Pennypack Creek. The Pennypack Creek at the Rhawn Street Bridge was above its 7 foot flood stage from 1138 a.m. EDT through 1202 p.m. EDT on the 4th. It crested at 7.40 feet at 1145 a.m. EDT.
A thunderstorm with heavy rain caused flash flooding along the Pennypack Creek as well as poor drainage flooding in northeastern Philadelphia. The Pennypack Creek at the Rhawn Street Bridge was above its 7 foot flood stage from 203 p.m. EDT through 239 p.m. EDT on the 4th. It crested at 7.78 feet at 215 p.m. EDT. Of the three times the Pennypack Creek flooded on the 4th, this was its highest crest of the day.
Thunderstorms with very heavy downpours caused flash flooding in the Spruce Hill section of Philadelphia, in particular around 43rd and Baltimore Streets. The precipitation total at the Philadelphia International Airport for September 4th was 3.12 inches.
For the third time in the same day, flooding occurred along the Pennypack Creek. The Pennypack Creek at the Rhawn Street Bridge was again above its 7 foot flood stage from 639 p.m. EDT through 713 p.m. EDT on the 4th. It crested at 7.50 feet at 645 p.m. EDT.
Thunderstorms with very heavy downpours caused flash flooding of small creeks and roadways in sections of Chestnut Hill, Hamilton, Jackson, Middle Smithfield and Stroud Townships. Doppler Radar storm total estimates exceeded 6 inches within the core of the heaviest rain. Pennsylvania State Route 191 near the former Penn Hills Resort in Stroud Township flooded. Flooding was also reported along sections of the Brodhead Creek that reached onto other roadways.
Thunderstorms with very heavy downpours caused flash flooding of small creeks as well as poor drainage and low lying area flooding in and around Stroudsburg. A precipitation event total of 5.75 inches was measured in East Stroudsburg.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Pennsylvania in 2012Every state in 2012This day in weather historyWarnings in Pennsylvania, September 2012
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: 412618, 412944, 412946, 412619, 412945, 412623, 412622.