160  
FXUS61 KPHI 240150  
AFDPHI  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ  
950 PM EDT TUE SEP 23 2014  
   
SYNOPSIS
 
 
HIGH PRESSURE OVER OUR FORECAST AREA WILL STRENGTHEN AS IT MOVES  
NORTHEAST...REACHING THE CANADIAN MARITIMES ON WEDNESDAY. A LOW  
PRESSURE SYSTEM WILL DEVELOP OFF THE CAROLINA COAST AND LIFT  
NORTHEAST INTO DELMARVA ON THURSDAY BEFORE MOVING OFFSHORE ON  
FRIDAY. ANOTHER HIGH PRESSURE FROM THE GREAT LAKES WILL BUILD INTO  
THE REGION FOR THE WEEKEND. A COLD FRONT IS EXPECTED TO MOVE  
THROUGH THE AREA MONDAY NIGHT FOLLOWED BY A HIGH PRESSURE SYSTEM  
BUILDING INTO NORTHERN NEW ENGLAND ON TUESDAY.  
 

 
   
NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/
 
 
930 PM ESTF: LITTLE CHANGE FROM THE 630 PM UPDATE. ADJUSTED  
SKYCOVER A BIT THE NEXT FEW HOURS.  
 
WINDS WERE DECREASED SLIGHTLY EARLY THIS EVENING PERMITTING IDEAL  
EVENING RADIATIONAL COOLING OVER MOST OF OUR FORECAST AREA.  
 
RAN THE UPS CROSSOVER FOG TOOL AND ONLY FOUND SOME ISOLATED SPOTTY  
FOG POTENTIAL IN SUSSEX COUNTY OF FAR NW NJ EARLY WEDNESDAY MORNING.  
 
SO FROM THE 330 PM DISCUSSION...  
FAIR WEATHER IS EXPECTED TONIGHT AS HIGH PRESSURE WILL  
BE ACROSS THE REGION. SKIES WILL BE MOSTLY CLR ACROSS THE  
NORTH...AND PARTLY CLOUDY ACROSS THE SOUTH WHERE SOME HIGH CI/CS  
CLOUDS WILL BE OBSERVED. A SLOW INCREASE IN HIGH CLOUDS WILL BE  
SEEN OVERNIGHT. LOW TEMPERATURES WILL AGAIN BE COOL WITH DECENT  
RADIATIONAL COOLING EXPECTED. I WENT BELOW MAV MOS IN MOST AREAS.  
LOWS WILL RANGE FROM THE LOW/MID 40S NORTH...TO THE LOW/MID 50S  
OVER THE DELMARVA AND METRO PHILADELPHIA. WINDS WILL BE LIGHT AND  
VARIABLE...THEN BECOME E/NE AT 5 TO 10 MPH BY DAWN.  
 

 
   
SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/
 
 
THE 630 PM ESTF RAISED POPS IN SOUTHERN TALBOT AND CAROLINE  
COUNTIES AS WELL AS SOUTHERN SUSSEX COUNTY DE WHERE IT SHOULD BE  
RAINING AT A PRETTY HEAVY CLIP VERY LATE IN THE DAY WEDNESDAY.  
THAT WITHIN THE 850 EASTERLY FLOW OF 35-40 KT.  
 
THE SFC HIGH WILL BE EAST OF THE AREA WED MORNING. LOW PRESSURE  
WILL BE DEEPENING OFF THE CAROLINA COASTAL AREAS AND BEGINNING TO  
TRACK N. CLOUDS WILL INCREASE ACROSS THE REGION DURING THE  
DAY...BUT THE ONLY CHC FOR RAIN WILL ONLY BE ACROSS SRN DELAWARE  
AND THE SOUTHERN COASTAL AREAS OF NJ. THESE RAIN CHCS WOULD BE  
DURING THE AFTERNOON ONLY. WINDS WILL INCREASE FROM THE E AT 10 TO  
20 MPH DURING THE DAY WITH GUSTS AROUND 25 MPH...POSSIBLY 30 ALONG  
THE COAST BY DAYS END. HIGH TEMPERATURES WILL MOSTLY BE IN THE LOW  
70S REGION- WIDE.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/
 
 
THE LONG TERM HAS BECOME MUCH MORE COMPLICATED WITH A GREATER  
IMPACT OVER OUR CWA THAN WAS THE CASE A COUPLE OF DAYS AGO. ALL OF  
THE MODELS ARE TRANSITIONING TO WHAT THE ECMWF AND CAN GGEM  
ORIGINALLY HAD. THE PROBLEM REMAINS IN THE DETAILS AS GULF STREAM  
CONVECTION WITH THIS DEVELOPING SYSTEM HAS RESULTED IN VERY  
LITTLE RUN TO RUN CONTINUITY AS TO THE LOCATIONS OF HEAVY RAIN.  
 
THAT BEING SAID, THE DP/DT ON THE SYSTEM HAS BEEN TOWARD A FASTER  
CLOSING OFF OF THE LOW (WHICH HAS ALREADY OCCURRED) AND THUS A  
MORE WESTWARD TUG BY IT ON THE SURFACE LOW. THE SPLIT OFF THE 12Z  
RUN IS WHETHER OR NOT THE LOW ALOFT WILL CLOSE AGAIN OVER PA.  
THIS MAKES ENDING OF PCPN CHANCES DIFFERENT. THE CAN GGEM QPF  
VERIFIED THE BEST THRU 12Z THIS MORNING, WHILE THE GFS LOOKED OFF  
TO THE BEST START OF THE 12Z MODELS IN THE SOUTHEAST.  
 
SINCE THE OP NAM LOOKED FAST GIVEN THE LOW HAS CLOSED FARTHER WEST  
THAN EARLIER PROJECTIONS, WE WENT CLOSER TO THE GFS TIMING. THE  
UKMET REMAINS THE MOST BENIGN MODEL WITH THIS EVENT, BUT GIVEN ITS  
BY ITSELF NOW WAS GIVEN LITTLE WEIGHT.  
 
WEDNESDAY NIGHT, RAIN, HEAVY AT TIMES WILL BE OVERSPREADING OUR CWA.  
POPS WERE INCREASED TO CAT EAST WHERE ALL THE MODELS HAVE DECENT  
MEASURABLE RAIN. HEAVY RAIN MENTION WAS KEPT EAST BASED ON MODELING  
CONSENSUS AND LOCATION OF THEIR 250MB DIVERGENCE ALOFT AND BETTER  
MID LEVEL FGEN FEATURES. WHILE SOME MODELS ARE SHOWING A SECONDARY  
PCPN MAX IN PA, THE PREDICTED PWATS ARE ABOUT HALF OF LOCALES  
CLOSER TO THE COAST. SFC BASED INSTABILITY IS NOT THERE, BUT SOME  
INSTABILITY IS BEING PREDICTED ALOFT. FOR NOW THE INSTABILITY IS  
TRAILING THE OMEGA VS BEING COINCIDENTAL IN OUR CWA, SO NO MENTION  
OF THUNDER. THAT BEING SAID THE PREDICTED CONVECTION TO OUR SOUTH  
IS NOT DOING WELL FOR MODEL QPF VERIFICATION. THERE HAS NOT BEEN  
MUCH RUN TO RUN CONTINUITY WITH REGARDS TO PLACEMENT OF HEAVY  
RAIN. THIS MODEL RUN SUITE DID NOT SEEM TO SUFFER FROM WHAT LOOKED  
LIKE FEEDBACK PBLMS THAT OCCURRED WITH SOME OF THE 00Z AND 06Z  
RUNS. WE ARE ENTERING THIS EVENT EXTREMELY DRY, EVEN FOR SEPTEMBER  
AND WOULD NEED MORE THAN THE 1 TO 3" PREDICTED FOR THIS EVENT FOR  
STREAMS AND RIVERS TO START HAVING PROBLEMS. SOME HEADWATER  
GUIDANCE IS NEAR 6 INCHES/12 HOURS. BIGGEST FLOODING ISSUES MAY  
BE ALONG THE IMMEDIATE COAST IF HEAVY RAIN COINCIDES WITH THE HIGH  
TIDE CYCLES. THERE SHOULD ALSO BE A RAIN IMPACT ON THE MORNING  
COMMUTE THURSDAY, ESPECIALLY IN THE NORTHERN TWO THIRDS OF OUR  
CWA.  
 
ON THURSDAY, THE SYNOPTIC SCALE PUSH OF HEAVIER RAIN IS EXPECTED TO  
MOVE THROUGH OUR CWA BY NOON. SECONDARY PCPN MAXES ARE NOW EITHER  
OFFSHORE OR NON GENERATED. NOW THAT THE MODELS HAVE KEYED IN FOR  
TWO SUCCESSIVE SOUNDING RUNS ON THE CLOSED LOW IN THE SE, THERE  
HAS BEEN A SLIGHTLY FASTER EVOLUTION OF THIS EVENT GOING FORWARD  
AND EVEN VS THE NIGHT RUN. DIFFERENCES ARISE AS TO HOW QUICKLY  
WILL THE TROF OR CLOSED LOW EXIT THE REGION. GIVEN THE DRIER AND  
FASTER TREND ON THE LATEST WRF AND ECMWF (ALTHOUGH THE LATTER IS  
STILL AMONG THE SLOWEST), WE DECREASED POPS FASTER ON THURSDAY  
AFTERNOON AND NIGHT AND HAVE FRIDAY DRY.  
 
ANOTHER WELL TIMED WEEKEND AS ALL OF THE MODELS HAVE US DRY AND  
UNSEASONABLY WARM IN THE WAKE OF THE DEPARTING LOW. THE NEXT  
BACKDOOR COLD FRONT SHOULD COME THROUGH LATER MONDAY OR TUESDAY.  
POPS WERE KEPT IN FOR MONDAY NIGHT AND ADDED FOR TUESDAY.  
 

 
   
AVIATION /02Z WEDNESDAY THROUGH SUNDAY/
 
 
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,  
KMIV, KACY AND SURROUNDING AREAS.  
 
TONIGHT...VFR MOSTLY CLEAR NORTHWEST TWO THIRDS AND VFR SCT-BKN CIRRUS  
AOA 20000 FT SOUTHEAST 1/3RD. LIGHT N-NE WIND.  
 
WEDNESDAY...VFR BKN-OVC CIRRUS AOA 20000 FT TO START THE DAY WITH A  
SCT-BKN DECK NEAR 3000 FT DEVELOPING NORTHWARD LATE MORNING AND  
AFTERNOON. E-NE WIND GUST 20 KT INTERIOR AND NEAR 25 KT COAST...ESPECIALLY  
AFTERNOON.  
 
OUTLOOK...  
WEDNESDAY NIGHT AND THURSDAY...MVFR TO IFR CEILINGS ARE LIKELY WITH  
MVFR VSBYS OVER MUCH OF THE REGION AS A LOW PASSES JUST EAST OF THE  
REGION. SOME GUSTY EAST WINDS ARE ALSO POSSIBLE FOR COASTAL  
AIRPORTS. THE TERMINALS EXPECTED TO HAVE THE LONGEST AND MOST  
SIGNIFICANT IMPACTS ARE KMIV AND KACY WITH AIRPORTS IN NJ AND DE  
OVERALL MOST AFFECTED.  
 
THURSDAY NIGHT AND FRIDAY...BECOMING VFR. GREATEST IMPACT ON  
THURSDAY NIGHT AND EARLY FRIDAY SHOULD BE FOG.  
 
FRIDAY NIGHT THROUGH SUNDAY. PRIMARILY VFR CONDITIONS EXPECTED. SOME  
EARLY MORNING FOG POSSIBLE AT MORE RURAL AIRPORTS AND TERMINALS.  
 

 
   
MARINE
 
 
NO HEADLINE OVERNIGHT. LAST GOOD NIGHT TO BE METEOROLOGICALLY SAFE  
ON THE ATLANTIC WATERS...POSSIBLY THROUGH SATURDAY.  
 
WEDNESDAY...SCA WIND GUSTS TO 25 KT SPREAD NORTHWARD DURING THE  
MORNING WITH 30 KT GUSTS BY LATE AFTERNOON. SEAS BUILD TO 5 FEET  
NNJ WATERS DURING THE AFTERNOON AND TO NEAR 8 OR 9 FT LATE DAY  
SOUTHERN NJ AND DE ATLANTIC WATERS. LIGHT RAIN WILL ARRIVE OVER  
THE SRN WATERS DURING WEDNESDAY AFTERNOON...THEN SPREAD N/W DURING  
THE EVENING.  
 
OUTLOOK...  
WEDNESDAY NIGHT AND THURSDAY...A GALE WATCH WAS ISSUED FOR MOST  
OF OUR COASTAL WATERS AS THERE SHOULD BE A PERIOD WHEN THE  
GRADIENT TIGHTENS TO THE POINT THAT GALES ARE POSSIBLE. LOWEST  
CONFIDENCE IN UPPER DELAWARE BAY AND OUR NORTHERN WATERS WHERE A  
SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH WEDNESDAY NIGHT.  
SLOW IMPROVEMENT WITH THE WINDS ON THURSDAY, DECREASING SOUTH  
FIRST. DELAWARE BAY MOST LIKELY TO GO BELOW SCA CONDITIONS ON  
THURSDAY.  
 
THURSDAY NIGHT THROUGH FRIDAY NIGHT...WINDS ON THE OCEAN SHOULD  
BE BELOW SCA CRITERIA BY FRIDAY MORNING WITH DELAWARE BAY  
REMAINING BELOW SCA CRITERIA. SEAS MAY BE ANOTHER PROBLEM AS THEY  
ARE PREDICTED TO BE SLOW TO SUBSIDE. SCA CONDITIONS FOR SEAS ARE  
POSSIBLE THRU FRIDAY NIGHT.  
 
SATURDAY AND SUNDAY...SUB SMALL CRAFT ADVISORY CONDITIONS ON  
DELAWARE BAY. SEAS SHOULD SUBSIDE BELOW SMALL CRAFT ADVISORY  
CRITERIA ON THE OCEAN ON SATURDAY AND REMAIN BELOW FOR THE REST OF  
THE WEEKEND.  
 

 
   
TIDES/COASTAL FLOODING
 
 
A 6 TO 18 HOUR PERIOD OF INTERMITTENT GALE FORCE EAST TO NORTHEAST  
WIND GUSTS (35KT) IS EXPECTED LATE WEDNESDAY INTO THURSDAY AND WILL  
PROBABLY CAUSE MINOR COASTAL FLOODING DURING ONE OR TWO OF THE 3  
HIGH TIDE CYCLES BEGINNING WEDNESDAY EVENING. THE TIDAL INUNDATION  
FLOOD RISK WILL LINGER THROUGH THE THURSDAY NIGHT HIGH TIDE CYCLE.  
 
NORMAL ASTRONOMICAL PREDICTIONS WITHOUT ANY METEOROLOGICAL INFLUENCE  
DO NOT INDICATE ANY UNUSUALLY HIGH TIDES.  
 
TIDES VERSUS PREDICTED LATE EARLY THIS TUESDAY EVENING (930 PM EDT)  
ARE GENERALLY WITHIN 1 INCH OF THE FORECAST VALUES ALONG THE  
ATLANTIC OCEAN.  
 
POSITIVE SURGE DEPARTURES ARE EXPECTED TO GROW RAPIDLY WEDNESDAY  
EVENING AND SUSTAIN THAT 1 TO 2 FOOT WEDNESDAY EVENING HIGH TIDE  
POSITIVE DEPARTURE THROUGH THE THURSDAY NIGHT HIGH TIDE CYCLE.  
 
IF THE SURGE IS 1.8 TO 2 FEET AND COINCIDES WITH THE HIGH TIDE...  
MINOR FLOODING WOULD OCCUR.  
 
THERE IS A SMALL CHANCE THAT THE SURGE AT THE TIME OF THURSDAY  
MORNING-MIDDAY HIGH TIDE WILL BE 2.3 FEET IN WHICH CASE MODERATE  
COASTAL FLOODING WOULD OCCUR.  
 
TIMING IS EVERYTHING IN THIS SITUATION.  
 
THIS IS NO SLAM DUNK FOR A MODERATE EVENT ...EVEN FOR MINOR THE  
GFS/NAM MODEL GUIDANCE IS RESISTANT TO FORECASTING EXCEEDANCE OF  
MINOR THRESHOLD. GFS/NAM CONTINUE CONSERVATIVE ON THEIR 18Z RUNS  
AND THE ONLY THE STEVENS INSTITUTE SSWS CHECKS IN WITH MINOR AT  
LEWES AND JUST BARELY.  
 
NO COASTAL FLOOD WATCH ATTM SINCE THE MODERATE COASTAL FLOOD THREAT  
APPEARS TO BE MARGINAL LOWER END AT WORST, AND ITS POSSIBILITY AS  
OF THIS WRITING APPEARS TO BE LESS THAN 25 PERCENT ALONG ANY  
STRETCH OF THE COAST.  
 
IF MODEL GUIDANCE AND FORECASTER CONFIDENCE FOR MODERATE COASTAL FLOODING  
INCREASES IN FUTURE FORECASTS...A COASTAL FLOOD WATCH WILL BE ISSUED.  
 
IN THE MEANTIME...MINOR COASTAL FLOODING APPEARS TO BE A GOOD BET  
FOR THE THURSDAY MORNING HIGH TIDE CYCLE, IF NOT ALREADY FOR THE  
DELAWARE ATLANTIC COAST WEDNESDAY EVENING.  
 
DEPENDING ON THE POSITION OF THE SURFACE LOW... THE COASTAL FLOOD  
THREAT MAY LINGER THURSDAY NIGHT OR EVEN FRIDAY MORNING AS THE STRONG  
ONSHORE WIND FIELD INITIALLY MOVES NORTH ALONG THE MID ATLANTIC  
COAST TOWARD LONG ISLAND ON THURSDAY AND THEN SLIDES SEWD WITH THE  
EASTWARD TURNING SURFACE LOW ON FRIDAY.  
 
SINCE THE WIND EVENT HAS YET TO BEGIN AND WE'RE NOT SEEING THE  
REALITY OF EASTERLY FLOW ON THE COASTAL TIDE GAGES AND EVEN MINOR  
FLOODING IS NOT YET A GUARANTEE ...WE ARE NOT YET POSTING AN  
ADVISORY AND THIS WAS CHECKED AGAINST THE 18Z MODELS.  
 
ONE ADDITIONAL NOTE...SOME BEACH EROSION IS LIKELY AND WAVES OF 10  
TO 12 FEET MAY ADD TO SPLASHOVER ONTO THE TYPICALLY VULNERABLE  
COASTAL BEACH PROPERTIES WEDNESDAY NIGHT AND THURSDAY.  
 
REVIEWING: THE PRIMARY GUIDANCE FOR THIS ANALYSIS DISCUSSION WAS  
THE 12Z GFS ESTOFS AND 18Z GFS ETSS WHICH SHOWED A 1-2 FOOT SURGE.  
THE NAM VIA DBOFS IS LESS THREATENING...WITH ONLY AROUND A HALF  
FOOT SURGE! THE STEVENS INSTITUTE SSWS WAS CHECKED AND LOOKS  
REASONABLE AND PREDICTS ABOUT A 6.4 TO 6.5 FOOT TIDE FOR LEWES  
DELAWARE WEDNESDAY EVENING AT 936 PM (A 1.9 FT SURGE).  
 

 
   
RIP CURRENTS
 
 
WE ISSUED A HIGH RISK FOR THE FORMATION OF DANGEROUS RIP CURRENTS  
IN OUR 8 PM FORECAST FOR SURF ZONE FORECAST FOR WEDNESDAY OVER  
DELAWARE AND HELD OFF FOR NJ PENDING ONE MORE MODEL CYCLE LOOK.  
 
IT APPEARS NJ WILL BE MODERATE DURING THE MORNING TRANSITIONING  
TO A HIGH RISK DURING MID AFTERNOON.  
 
A MODERATE OR HIGH RISK FOR THE FORMATION OF THE DANGEROUS RIP  
CURRENTS WILL LINGER THURSDAY.  
 
THE ENHANCED RISK FOR RIP CURRENTS MIGHT PERSIST INTO FRIDAY EVEN  
AS WINDS DIMINISH AND SEAS SLOWLY SUBSIDE.  
 

 
   
PHI WATCHES/WARNINGS/ADVISORIES
 
 
PA...NONE.  
NJ...NONE.  
DE...HIGH RIP CURRENT RISK FROM 8 AM EDT WEDNESDAY THROUGH  
WEDNESDAY EVENING FOR DEZ004.  
MD...NONE.  
MARINE...GALE WATCH FROM WEDNESDAY EVENING THROUGH LATE WEDNESDAY NIGHT  
FOR ANZ431-451>455.  
SMALL CRAFT ADVISORY FROM 6 AM TO 8 PM EDT WEDNESDAY FOR  
ANZ431-451>455.  
SMALL CRAFT ADVISORY FROM 6 AM WEDNESDAY TO 6 AM EDT THURSDAY  
FOR ANZ430-450.  
 

 
 

 
SYNOPSIS...GIGI/JOHNSON  
NEAR TERM...DRAG/O'HARA 950  
SHORT TERM...DRAG/O'HARA  
LONG TERM...GIGI  
AVIATION...DRAG/GIGI/JOHNSON/O'HARA 950  
MARINE...DRAG/GIGI/JOHNSON/O'HARA 950  
TIDES/COASTAL FLOODING...950  
RIP CURRENTS...950  
 
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