AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1050 AM EDT SAT AUG 27 2011
.SYNOPSIS...
HURRICANE IRENE WILL IMPACT OUR REGION OVER THE WEEKEND. AS THE
REMNANTS OF THE SYSTEM MOVE UP INTO EASTERN CANADA ON MONDAY, HIGH
PRESSURE FROM THE WEST SHOULD BEGIN TO BUILD INTO EASTERN
PENNSYLVANIA, NORTHEASTERN MARYLAND, DELAWARE AND NEW JERSEY. THE
HIGH IS FORECAST TO INFLUENCE OUR REGION FOR MUCH OF THE NEW WEEK.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...-- Changed Discussion --
**SIGNIFICANT TO DAMAGING AFFECTS FROM HURRICANE IRENE ACROSS THE REGION ESPECIALLY LATER TODAY THROUGH ABOUT MIDDAY SUNDAY.** BASED ON THE NHC WINDS AS WELL AS FORECAST SOUNDINGS, IT APPEARS THAT OUR FAR WESTERN/NORTHWESTERN ZONES MAY VERY WELL EXPERIENCE A PERIOD OF TROPICAL STORM FORCE WINDS LATE TONIGHT AND SUNDAY MORNING. AS A RESULT, WE EXPANDED THE TROPICAL STORM WARNING TO COVER THE REMAINDER OF THE CWA /WFO`S CTP AND BGM HAVE ISSUED WIND RELATED HEADLINES/. IT APPEARS SOME DRY AIR IS BEING ENTRAINED INTO THE HURRICANE AS THE CONVECTION HAS REALLY BEEN ERODING ON THE SOUTHWEST SIDE OF THE CIRCULATION. BASED ON THE HURRICANE HUNTER AIRCRAFT OBSERVATIONS, DESPITE PLENTY OF WIND AT 700 MB IT APPEARS IT IS HAVING A TOUGH TIME REALLY MIXING DOWN TO THE SURFACE PLUS THE STORM HAS LOST SOME OF ITS ORGANIZATION. AS A RESULT OF THIS AND EVENTUAL LAND INTERACTION, NHC HAS LOWERED THE INTENSITY AS IT TRACKS BY OUR AREA SUNDAY. THIS IS A LARGE HURRICANE, THEREFORE DO NOT LET YOUR GUARD DOWN. EVERYONE SHOULD BE PREPARED FOR THIS LARGE STORM AS IT TAKES AIM ON OUR CWA. A PLAN SHOULD NOW BE IN PLACE, AND KEEP UPDATED ON THE WEATHER FORECASTS. CHECK THE HURRICANE LOCAL STATEMENT FOR MORE DETAILED INFORMATION. THE FIRST MAJOR RAIN BAND HAD MOVED ONSHORE AND INTO SOUTHERN NJ, CENTRAL AND SOUTHERN DELAWARE AND MOST OF THE MARYLAND EASTERN SHORE AS OF LATE THIS MORNING. WE WERE STARTING TO SEE SMALL SCALE CIRUCLATIONS IN THE LOWER LEVELS MOVING ONTO THE COAST JUST SOUTH OF DELAWARE. GUSTS WERE ABOUT 30 KNOTS ON LAND OVER OUR FAR SOUTHERN ZONES. THE EVENT HAS BEGUN FOR OUR AREA. WE CONTINUE TO CONSIDER A COASTAL FRONT THAT HAS MOSTLY SET UP SHOP FARTHER INLAND. THE LOCATION OF THIS FEATURE WILL BE CRUCIAL IN DETERMINING WHERE THE HEAVY RAIN AXIS OCCURS. IT APPEARS THIS WILL BE CLOSE TO THE INTERSTATE 95 CORRIDOR, HOWEVER IT WILL DEPEND ON THE EXACT TRACK OF THE CENTER OF HURRICANE IRENE. AS THE HURRICANE MOVES TO OUR LATITUDE, THE MASSIVE ONSHORE FLOW WILL PROBABLY TEND TO WRAP THE SURFACE FRONT WESTWARD AND THEN SOUTHWARD DUE TO ITS LARGE CIRCULATION. THE INFLUX OF PLENTY OF MOISTURE ALONG WITH THE SURFACE FRONT WILL RESULT IN AN EFFICIENT OVERRUNNING SURFACE. THIS WILL RESULT IN EXCESSIVE RAINFALL. FOR MORE INFORMATION ABOUT THE HEAVY RAIN THREAT, SEE THE HYDROLOGY SECTION BELOW. WE WOULD LIKE TO CONTINUE TO STRESS THAT IT IS IMPORTANT TO NOT FOCUS ON THE EXACT CENTER OF THE HURRICANE, ESPECIALLY SINCE THIS PARTICULAR STORM IS A VERY LARGE SYSTEM. WE EXPECT WIDESPREAD IMPACTS FROM THIS HURRICANE ACROSS THE CWA. WE GENERALLY LEANED CLOSER TO THE GFS REGARDING POPS AS IT APPEARS TO HAVE A DECENT HANDLE ON THE RAIN SHIELD HEADED TOWARD OUR SOUTHEAST ZONES EARLY THIS MORNING. THE INCREASING FLOW ALONG WITH DEEPENING MOISTURE WILL ALLOW FOR SOME CONVECTION TO BE ESPECIALLY EMBEDDED. WHILE THE TORNADO POTENTIAL IS LOW, IT IS NOT ZERO AS SOME MINI-SUPERCELL STRUCTURES WILL BE POSSIBLE NORTH OF THE CENTER AS THEY SLIDE ONSHORE. A TORNADO WATCH HAS BEEN ISSUED JUST TO OUR SOUTH.
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SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... MOST OF THIS TIME FRAME WILL BE DOMINATED BY HURRICANE IRENE AS IT MOVES VERY NEAR OUR COAST SUNDAY MORNING. THE WORST CONDITIONS WILL BE TONIGHT AND SUNDAY MORNING. THERE IS A HIGH RISK OF AREAS OF DAMAGING WINDS AND HEAVY/POSSIBLY RECORD SETTING RAINFALL THROUGH SUNDAY MORNING. OUR WIND FORECAST IS BASED OFF OF THE GRIDDED WIND FIELD FROM THE OFFICIAL NHC FORECAST AND THIS WILL BE UPDATED WITH SUBSEQUENT ADVISORY ISSUANCES. WE GENERALLY BASED OUR POPS MORE TOWARD A BLEND WHICH ENDS UP SIMILAR TO THE GFS. INTERESTINGLY ENOUGH, THE WATER VAPOR EARLY THIS MORNING SHOWS A MID LEVEL TROUGH CRUISING THROUGH THE GREAT LAKES REGION. THE FLOW STRENGTHENING AHEAD OF THIS CAN BE SEEN BY THE OUTFLOW FROM HURRICANE IRENE EXPANDING IN SIZE AND NORTHWARD. THIS SHORT WAVE TROUGH APPEARS TO BE MOVING RATHER QUICKLY EASTWARD, WHICH MAY END UP NUDGING IRENE A BIT FARTHER TO THE EAST. A LOT OF THE MODEL GUIDANCE INDICATES THE STRONGEST BOUNDARY LAYER WINDS STAY NEAR THE COAST AND THEN OVER THE OCEAN, WITH FRICTIONAL EFFECTS REDUCING THE SURFACE WINDS INLAND. BASED ON THIS, THE WESTERN PART OF THE HURRICANE WARNING INCLUDING PHILADELPHIA MAY NOT QUITE MAKE IT WITH WINDS MOSTLY IN THE TROPICAL STORM FORCE RANGE. GIVEN THE LARGE WIND FIELD, WE WILL NOT CHANGE THESE ATTM. OVERALL, THERE CONTINUES TO BE A HIGH RISK OF IMPACTS WITH THIS HURRICANE, WHICH INCLUDES DAMAGING WINDS, TORRENTIAL RAIN, COASTAL FLOODING, DANGEROUS RIP CURRENTS, AND BATTERING WAVES AND BEACH EROSION. MUCH OF THE MODEL GUIDANCE STILL SHOWS THE DEVELOPMENT OF A STRONG 250 MB JET NORTH OF THE HURRICANE INTO SUNDAY, GENERALLY FROM THE EASTERN GREAT LAKES TO NORTHERN NEW ENGLAND. THIS UPPER-LEVEL JET EVEN HAS SOME ANTICYCLONIC CURVATURE TO IT AND GIVEN THE ORIENTATION OF THIS JET IT IS SUCH THAT IRENE IS WITHIN THE RIGHT ENTRANCE REGION AS SHE TRACKS NORTHWARD. THIS SCENARIO MAY TEND TO HELP WITH A POLEWARD UPPER-LEVEL OUTFLOW CHANNEL AND ASSIST IN THE INTENSITY OF THE SYSTEM AS A WHOLE. THEREFORE, DESPITE SOME INCREASING SHEAR AS THE HURRICANE GAINES LATITUDE ALONG WITH COOLER WATERS AND LAND INTERACTIONS, PERHAPS THIS IS WHY MUCH OF THE MODEL GUIDANCE NEARLY INSISTS THIS SYSTEM MAINTAINS A RATHER LOW CENTRAL PRESSURE ALL THE WAY INTO SOUTHERN NEW ENGLAND. IT BECOMES EVEN MORE OF AN INTENSITY FORECAST CHALLENGE AS TROPICAL CYCLONES GET THIS FAR NORTH AND INTERACT WITH BAROCLINIC ZONES AND LARGE SCALE SYNOPTIC FEATURES. THE PRESENCE OF THE SURFACE FRONT AND UPPER-LEVEL JET IS CONCERNING AS THIS MAY PLAY A SIGNIFICANT ROLE IN ENHANCING THE RAINFALL RATES. THE AMOUNT OF RAIN THAT LOOKS TO OCCUR WITH THIS SYSTEM MAY END UP BEING THE MAIN TOPIC OF DISCUSSION FOR MANY YEARS. AN EXAMINATION OF THE WIND FIELD AT 925 MB IS STILL CONCERNING WITH A LARGE AREA OF 60 TO NEARLY 85 KNOTS TRACKING ACROSS THE CWA THIS EVENING THROUGH SUNDAY MORNING. WHILE THE FRICTIONAL EFFECTS WILL TEND TO SLOW THE WIND DOWN SOME AND ALSO ALLOW FOR SOME DECOUPLING BETWEEN THE SURFACE AND ABOVE, THE PRESSURE GRADIENT COMBINED WITH ENHANCED MIXING WITHIN HEAVIER RAIN/CONVECTION SHOULD PRODUCE SIGNIFICANT/DAMAGING GUSTS. ONE THING NOTED IS THE MODEL FORECASTS INDICATING A RATHER IMPRESSIVE 3-HOUR PRESSURE RISE BEHIND THE HURRICANE SUNDAY AFTERNOON. SOME FORECAST SOUNDINGS INDICATE THE POTENTIAL FOR AN INCREASED THREAT OF DAMAGING GUSTS TO OCCUR AS THIS FEATURE MOVES THROUGH AND VERTICAL MIXING SHARPLY INCREASES DUE TO SOME CLEARING. IF THIS WERE TO PAN OUT, THE WINDS COULD BE STRONGEST WHEN THIS SHARP PRESSURE FALL/RISE COUPLET MOVES THROUGH. WE CONTINUE TO USE A 125 PERCENT OF THE SUSTAINED WINDS TO DERIVE OUR GUSTS BUT NOW CAPPED THEM AT 75 KNOTS /20 PERCENT REDUCTION OF THE SUSTAINED WINDS OVER LAND/. THE WIND GUST TOOL THAT INCLUDES MIXING MAY BE TO HIGH ESPECIALLY OVER AREAS FARTHER INLAND. IT APPEARS THAT THE HURRICANE WILL SPEED UP SOME, AND THIS FORWARD MOTION COULD BE A BIT MORE IF THE INCOMING SHORT WAVE TROUGH IS ENOUGH TO PICK IT UP QUICKER. WE THEREFORE CONTINUED THE TREND IN QUICKLY TAPERING POPS DOWN SUNDAY AFTERNOON FROM SOUTH TO NORTH. ONCE THE STORM MOVES OFF TO THE NORTH AND NORTHEAST LATER SUNDAY, THE CONDITIONS WILL QUICKLY IMPROVE. && .LONG TERM /MONDAY THROUGH FRIDAY/... OVERALL A MUCH CALMER TIME PERIOD MONDAY THROUGH FRIDAY AS THE WIND WILL QUICKLY DIMINISH MONDAY AS HIGH PRESSURE BEGINS TO BUILD IN. A WEAK TROUGH WILL SKIRT OUR REGION TUESDAY, WHICH MAY INCREASE CLOUDS A BIT. HIGH PRESSURE THEN BUILDS ACROSS ON WEDNESDAY BEFORE SLIPPING TO THE EAST THURSDAY. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY AND SURROUNDING AREAS. RAIN WITH EMBEDDED HEAVIER SHOWERS AND ISOLATED TSTMS WILL ADVANCE FROM THE SOUTHEAST DURING THE COURSE OF THE DAY TODAY. THIS IS EXPECTED TO TRANSITION TO A WIND DRIVEN RAIN THIS EVENING WITH THE WORST CONDITIONS EXPECTED LATER TONIGHT AND SUNDAY MORNING. THEREFORE, WE INDICATED CONDITIONS EVERYWHERE AT SUB-VFR WITH PERIODS OF HEAVY RAIN. WHILE SOME THUNDERSTORMS SHOULD BE EMBEDDED IN THE RAIN SHIELD, WE OPTED TO NOT INCLUDE IT AT THIS TIME GIVEN LOW CONFIDENCE ON TIMING AND COVERAGE. ANY HEAVIER RAIN AND THUNDER WILL HAVE THE POTENTIAL TO PRODUCE STRONGER SURFACE GUSTS. OTHERWISE, WE GRADUALLY INCREASED THE WINDS THIS AFTERNOON AND ESPECIALLY TONIGHT. WE WENT CONSERVATIVE WITH THE GUSTS AS IT IS NOT COMPLETELY CLEAR HOW MUCH TRANSFER OF THE WINDS TO THE SURFACE FROM ALOFT OCCURS. WE CARRIED THE STRONGEST WINDS AT KMIV AND KACY AT THIS POINT. THERE COULD BE A SECONDARY SURGE OF RATHER STRONG WINDS FOR A FEW HOURS SUNDAY AFTERNOON AS THE CENTER OF THE STORM MOVES THROUGH AND A SHARP PRESSURE RISE OCCURS. THE WINDS WILL BE SOUTHEAST TO EAST THEN SHIFT TO THE NORTHEAST THROUGH TONIGHT. OUTLOOK... HIGH PRESSURE WILL LIKELY INFLUENCE OUR REGION FROM MONDAY THROUGH WEDNESDAY, WITH DRY WEATHER AND MAINLY VFR CONDITIONS. HOWEVER, SOME LATE NIGHT AND EARLY MORNING VISIBILITY RESTRICTIONS ARE POSSIBLE EACH DAY.
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.MARINE...
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A HURRICANE WARNING REMAINS IN EFFECT FOR ALL ZONES. THE ARRIVAL OF THE HURRICANE WILL GENERATE INCREASING WINDS FROM THE EAST AND NORTHEAST. THE TRACK APPEARS TO TAKE THE CENTER OF THE STORM OVER OR VERY NEAR OUR COASTAL WATERS AFTER MIDNIGHT TONIGHT. THIS IS A LARGE SYSTEM THEREFORE THE WIND FIELD IS RATHER EXTENSIVE. THE SIZE OF THIS SYSTEM IS ALSO AIDING IN A LARGE FIELD OF HIGH SEAS. THESE SEAS WILL CONTINUE TO BUILD TODAY AND PEAK LATE TONIGHT AND SUNDAY MORNING AS THE CENTER MOVES ON BY. THERE COULD BE A SECONDARY SURGE OF WINDS FOR A FEW HOURS SUNDAY AFTERNOON AS IMPRESSIVE 3-HOUR PRESSURE RISES MOVE THROUGH. WE GENERALLY FOLLOWED WAVEWATCH FAIRLY CLOSELY BUT LEANED CLOSER TO CONTINUITY REGARDING THE SUBSIDING OF THE SEAS LATE SUNDAY INTO MONDAY. AS OF NOW, WE HAVE SEAS PEAKING BETWEEN 20-25 FEET. THE CONDITIONS ARE EXPECTED TO IMPROVE SUNDAY NIGHT INTO MONDAY AS THE SYSTEM MOVES WELL TO OUR NORTH AND THE PRESSURE GRADIENT EASES SIGNIFICANTLY. THE OFFSHORE WINDS IN THE WAKE OF IRENE SHOULD ALLOW THE SEAS TO SUBSIDE FAIRLY QUICKLY OVERALL. OUTLOOK... HIGH PRESSURE WILL LIKELY INFLUENCE THE COASTAL WATERS OF NEW JERSEY AND DELAWARE FROM MONDAY THROUGH WEDNESDAY. WIND SPEEDS ARE FORECAST TO STAY GENERALLY LESS THAN 15 KNOTS. WAVE HEIGHTS ON OUR OCEAN WATERS SHOULD REMAIN HIGH ON MONDAY IN THE WAKE OF HURRICANE IRENE. WAVE HEIGHTS ARE EXPECTED TO SUBSIDE SLOWLY ON TUESDAY AND WEDNESDAY.
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HYDROLOGY... HEAVY AND POSSIBLY RECORD SETTING RAINFALL TODAY AND SUNDAY MAY RESULT IN MAJOR FLOODING ACROSS THE AREA. THE PW VALUES FORECAST ACROSS THE REGION ARE RATHER IMPRESSIVE WITH 2.0-2.5 INCHES OVERSPREADING THE REGION TODAY INTO SUNDAY. IF THE CENTER GETS CLOSE ENOUGH TO THE COAST, SOME GUIDANCE INDICATES THE PW VALUES INCREASE TO JUST OVER 3.0 INCHES. THIS AMOUNT OF MOISTURE IN THE ATMOSPHERE WILL LEAD TO EXCESSIVE RAINFALL RATES AND TOTALS. THIS COMBINED WITH ANY UPSLOPE ENHANCEMENT AND/OR LOCALLY ENHANCED CONVERGENCE/BANDING WILL ADD TO THE RAIN RATES. THE INITIAL INFLUX OF THIS HIGHER MOISTURE CONTENT AIR ALONG WITH THE PRESENCE OF A STATIONARY FRONT WILL LEAD TO BOUTS OF LOCALLY VERY HEAVY DOWNPOURS WELL BEFORE THE HURRICANE GETS TO OUR LATITUDE. SMALLER CREEKS AND STREAMS WILL BE HIGHLY SUSCEPTIBLE TO RAPID FLOODING. THE RARITAN AND SCHUYLKILL RIVERS HAVE THE POTENTIAL TO REACT RATHER QUICKLY AND ALSO ARE HIGHLY SUSCEPTIBLE TO FLOODING. THE DELAWARE, SUSQUEHANNA, RANCOCAS AND PASSAIC RIVERS REACT MORE SLOWLY, BUT THEY ALSO ARE HIGHLY SUSCEPTIBLE TO FLOODING. IN ADDITION, THE WINDSWEPT RAIN WILL LIKELY PRODUCE URBAN AND POOR DRAINAGE FLOODING. THE STRONG ONSHORE FLOW COMBINED WITH THE TIDES WILL TEND TO BACK WATER UP, COMPLICATING FLOODING PROBLEMS. GIVEN THE QPF FORECAST /6 TO 10 INCHES WITH LOCALLY UP TO 12 INCHES/ AND THE ANTECEDENT CONDITIONS, THE FLOOD WATCH REMAINS IN EFFECT AND WE CONTINUE TO CARRY A HEAVY RAIN MENTION IN THE FORECAST. .TIDES/COASTAL FLOODING... THE THREAT OF MODERATE TO SEVERE COASTAL FLOODING REMAINS HIGH OVER THE WEEKEND AS HURRICANE IRENE IMPACTS OUR REGION. THE SUNDAY MORNING HIGH TIDE ALONG THE OCEANFRONT AND DELAWARE BAY IS OF MOST CONCERN. HOWEVER, WITH THE STRENGTH OF THE STORM, COASTAL FLOODING MAY VERY WELL BE AN ISSUE FOR HOURS BEFORE AND AFTER THE HIGH TIDE OCCURS. WITH WATER EXPECTED TO BE PUSHED UP DELAWARE BAY, FLOODING IS ALSO A CONCERN FOR THE TIDAL PORTION OF THE DELAWARE RIVER. COASTAL FLOODING ISSUES MAY LINGER INTO THE SUNDAY EVENING HIGH TIDE, ESPECIALLY ALONG THE NORTHERN PART OF THE NEW JERSEY COAST AND ALONG RARITAN BAY. .RIP CURRENTS... DANGEROUS RIP CURRENTS ASSOCIATED WITH HURRICANE IRENE ARE ANTICIPATED THROUGH THE ENTIRE WEEKEND.
George Wright is a Certified Consulting Meteorologist for Wright Weather Consulting, LLC. George is also a meteorologist with ABC News and Cablevision News 12. Our website is WrightWeather.com.
