738
FXUS61 KPHI 191705
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
105 PM EDT SAT SEP 19 2026
WHAT HAS CHANGED
UPDATED AVIATION AND KEY MESSAGE 1 SECTIONS WITH LATEST
GUIDANCE.
KEY MESSAGES
1. LOW AND COLD FRONT MOVE THROUGH THE REGION TONIGHT INTO
SUNDAY WITH RAIN SHOWERS LIKELY.
2. A STATIONARY FRONT SOUTH OF THE REGION COULD KEEP RAIN
CHANCES AROUND, ESPECIALLY FOR DELMARVA THROUGH MID WEEK.
3. A CLOSED LOW COULD DEVELOP OFF OUR COAST BY THURSDAY,
POTENTIALLY BRINGING ANOTHER CHANCE FOR RAIN, AND INCREASING THE
RISK FOR COASTAL FLOODING.
DISCUSSION
KEY MESSAGE 1...LOW AND COLD FRONT MOVE THROUGH THE REGION
TONIGHT INTO SUNDAY WITH RAIN SHOWERS LIKELY.
HIGH PRESSURE SHIFTS AWAY FROM THE REGION LATE TONIGHT AS A LOW
ORGANIZES AND DEVELOPS OVER THE MIDWEST. THE WARM FRONT
ASSOCIATED WITH THIS LOW WILL MOVE NORTHWARD INTO THE REGION
EARLY SUNDAY AFTERNOON, BUT WILL BE QUICKLY FOLLOWED BY A COLD
FRONT SUNDAY EVENING.
REGARDLESS OF THE EXACT EVOLUTION OF THE WARM FRONT, THE LEADING
EDGE OF A LARGE AREA OF RAIN WILL MOVE INTO THE REGION BY LATE
THIS EVENING IN RESPONSE TO MODEST MID AND UPPER LEVEL SYNOPTIC
SCALE LIFT ASSOCIATE WITH THE CYCLOGENSIS. LOCATIONS NORTH OF
PHILADELPHIA WILL HAVE THE GREATEST CHANCE FOR A PROLONGED
PERIOD OF RAINFALL TONIGHT INTO SUNDAY.
AN EASTERLY FLOW WILL BE IN PLACE THIS EVENING THROUGH TONIGHT,
BECOMING SOUTHEASTERLY BY SUNDAY MORNING. AS SUCH, LOW LEVEL
MOISTURE WILL BE ON THE INCREASE, WITH SURFACE DEW POINTS RISING
WELL INTO THE 60S AND PRECIPITABLE WATER VALUES INCREASING TO
NEAR 2 INCHES. PRECIPITABLE WATER VALUES THAT HIGH ARE WELL
ABOVE THE 90TH PERCENTILE.
THE RISK FOR EXCESSIVE RAINFALL IS A MARGINAL, OR 1 OUT OF 4,
THROUGH THIS PERIOD. HOWEVER, WITH ABUNDANT MOISTURE, LOCALLY
HEAVY RAIN WILL STILL BE POSSIBLE, AND IF IT OCCURS OVER URBAN
AND OTHER POOR DRAINAGE AREAS, LOCALIZED FLASH FLOODING IS
POSSIBLE.
KEY MESSAGE 2...A STATIONARY FRONT SOUTH OF THE REGION COULD
KEEP RAIN CHANCES AROUND, ESPECIALLY FOR DELMARVA THROUGH MID
WEEK.
ONCE THE COLD FRONT SWEEPS THROUGH ON MONDAY, IT IS EXPECTED TO
STALL SOUTH OF OUR REGION. HOW FAR SOUTH THAT FRONT STALLS WILL
BE A BIG FACTOR IN HOW MUCH RAIN WE SEE THROUGH THE WEEK. THE
FURTHER SOUTH IT STALLS, THE LESS LIKELY OUR REGION WILL SEE
CONTINUED RAIN CHANCES THROUGH MID WEEK. REGARDLESS, OUR REGION
SHOULD GENERALLY BE ON THE COOL SIDE OF THE FRONT THROUGH THIS
PERIOD KEEPING TEMPERATURES BELOW NORMAL AND LOW LEVEL MOISTURE
LOWER THAN WHAT IT IS EXPECTED TO BE ON SUNDAY.
AN UPPER LEVEL LOW DIGGING IN FROM THE NORTHWEST COULD SPARK
ANOTHER ROUND OF CYCLOGENSIS BY WEDNESDAY, WHICH COULD RESULT IN
THE STATIONARY FRONT SLIDING NORTH AS A WARM FRONT BRIEFLY,
THOUGH IT WILL STILL LIKELY STAY SOUTH OF OUR REGION.
KEY MESSAGE 3...A CLOSED LOW COULD DEVELOP OFF OUR COAST BY
THURSDAY, POTENTIALLY BRINGING ANOTHER CHANCE FOR RAIN, AND
INCREASING THE RISK FOR COASTAL FLOODING.
AS EARLY AS TUESDAY, THERE LOOKS TO BE AN INVERTED SURFACE
TROUGH OFF THE COAST OF THE CAROLINAS. HOWEVER, MOST MODELS
DON'T SHOW THIS LOW CLOSING OFF UNTIL WEDNESDAY OR THURSDAY.
THAT IS NOT THE ONLY WAY THE MODELS DIFFER; THERE ARE
SIGNIFICANT DIFFERENCES IN THE TRACK OF THE LOW, RANGING FROM
THE GFS SHOWING THE CENTER OF THE LOW AS CLOSE AS 120 MILES FROM
OUR COAST, TO THE ICON, WITH THE CENTER OF THE LOW GETTING NO
CLOSER THAN 500 MILES FROM OUR COAST!
THE CLOSER THE TRACK OF THIS LOW IS TO THE COAST, THE MORE
LIKELY OUR REGION IS TO SEE RAIN, AND GUSTY WINDS IN THE
THURSDAY AND FRIDAY TIME PERIOD.
IT ALSO BEARS WATCHING AS IT COULD INCREASE THE RISK FOR COASTAL
FLOODING. THE FULL MOON IS ON SATURDAY, SEPT 26, SO PERSISTENT
ONSHORE FLOW THURSDAY AND FRIDAY WILL ONLY INCREASE THE RISK AS
ASTRONOMICAL TIDES INCREASE AHEAD OF THE FULL MOON.
AVIATION /18Z SATURDAY THROUGH THURSDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY AND SURROUNDING AREAS.
VFR CONDITIONS ARE EXPECTED THROUGH AT LEAST 00Z. AFTER 00Z,
MVFR CEILINGS ARE LIKELY TO START BUILDING IN FROM THE WEST AS
AREAS OF RAIN APPROACH. ANOTHER AREA OF LOW CLOUDS MAY BUILD IN
FROM THE EAST DUE TO ONSHORE FLOW/MARINE STRATUS MOVING IN.
WINDS ARE EXPECTED TO GRADUALLY VEER FROM E TO SE TO S THROUGH
THE TAF PERIOD. WIND SPEEDS WILL BE 10 TO 15 KNOTS THIS
AFTERNOON, AND AT OR BELOW 10KT THEREAFTER.
OUTLOOK...
SUNDAY NIGHT THROUGH MONDAY...PERIODS OF MVFR CONDITIONS IN RAIN
AND LOW CLOUDS.
TUESDAY THROUGH THURSDAY...SUB-VFR CONDITIONS POSSIBLE WITH
SHOWERS AROUND WITH BREEZY NORTHEAST WINDS.
MARINE
EASTERLY WINDS WILL DIMINISH TO 10 TO 15 KNOTS BY LATE THIS
AFETRNOON, WITH SEAS LESS THAN 5 FEET.
ONCE WINDS AND SEAS SUBSIDE, CONDITIONS ARE EXPECTED TO REMAIN
BELOW SCA CRITERIA THROUGH SUNDAY NIGHT.
OUTLOOK...
MONDAY THROUGH WEDNESDAY...SCA HEADLINES MAY BE NEEDED STARTING
ON MONDAY FOR EAST TO NORTHEAST WINDS 15 TO 20 KT WITH GUSTS UP
TO 25 KT AND 4 TO 6 FT. GALE FORCE WINDS ARE POSSIBLE AS EARLY
AS TUESDAY WITH WIND GUSTS EXCEEDING 35 KTS. SEAS MAY BUILD AS
HIGH AS 10 TO 15 FT FROM TUESDAY THROUGH THURSDAY.
LOOKING AHEAD, THERE IS AT LEAST A CHANCE FOR GALE CONDITIONS
THROUGH FRIDAY. HOWEVER, IT WILL BE HIGHLY DEPENDENT ON THE
TRACK OF A COASTAL LOW.
RIP CURRENTS...
SATURDAY...EAST WINDS AROUND 15 MPH WITH GUSTS UP TO 20 MPH.
EASTERLY SWELLS WITH A 10 TO 12 SECOND PERIOD. AS A RESULT, THERE IS
A MODERATE RISK FOR THE DEVELOPMENT OF DANGEROUS AND LIFE
THREATENING RIP CURRENTS FOR MONMOUTH COUNTY AND OCEAN COUNTY SHORES
AND A LOW RISK FOR ATLANTIC COUNTY AND COASTAL CAPE MAY COUNTY
SHORES AND DELAWARE BEACHES.
SUNDAY...THE WINDS SHIFT TO SOUTH/SOUTHEAST BUT REMAIN AROUND 15 TO
20 MPH. BREAKING WAVE HEIGHTS IN THE SURF ZONE LOOK TO BE AROUND 3
TO 4 FEET FOR THE JERSEY SHORE AND 2 TO 4 FEET FOR THE DELAWARE
BEACHES. THERE IS A FORECAST OF A MODERATE RISK OF DANGEROUS
AND LIFE THREATENING RIP CURRENTS ALONG THE NJ AND DE COAST.
FOR SPECIFIC BEACH FORECASTS, VISIT WEATHER.GOV/BEACH/PHI
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR
ANZ450>452.
DISCUSSION...WFO PHI
AVIATION...WFO PHI
MARINE...WFO PHI
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