| http://www.hpc.ncep.noaa.gov/discussions/hpcdiscussions.php?disc=pmdepd PRELIMINARY EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER COLLEGE PARK MD 436 AM EDT FRI OCT 26 2012 VALID 12Z TUE OCT 30 2012 - 12Z FRI NOV 02 2012 ...HURRICANE/POST-TROPICAL CYCLONE SANDY IS LIKELY TO SPREAD HIGH WINDS/HEAVY RAINS/HEAVY MOUNTAIN SNOWS FROM THE CAROLINAS AND CENTRAL APPALACHIANS NORTHWARD INTO CANADA... GENERAL FLOW PATTERN ==================== A RETROGRADING POSITIVE ANOMALY MOVING FROM SOUTHERN GREENLAND INTO NORTHERN QUEBEC FAVORS A QUASI-STATIONARY DEEP CYCLONE NEAR THE NORTHEAST, IN THIS CASE HURRICANE SANDY AND ITS POST-TROPICAL REMAINS. OTHERWISE...RIDGING IS GENERAL EXPECTED OUT WEST...THOUGH QUASI-ZONAL FLOW ACROSS THE PACIFIC IS EXPECTED TO SEND ENERGY ACROSS THE NORTHWEST. THE GUIDANCE IS IN EXCELLENT AGREEMENT ON THE GENERAL FLOW PATTERN, THOUGH LARGE DETAIL ISSUES REMAIN WITH SANDY'S FUTURE COURSE AND STRENGTH, KEEPING CERTAINTY IN THE PATTERN ACROSS THE NORTHEAST BELOW AVERAGE. MODEL PREFERENCE ================ THE NATIONAL HURRICANE CENTER (NHC) TRACK BEST RESEMBLES A 40/20/20/20 BLEND OF THE 12Z ECMWF ENSEMBLE MEAN/00Z ECMWF/00Z GFS/00Z UKMET, WHICH WAS USED FOR MONDAY THROUGH WEDNESDAY. FOR THURSDAY AND NEXT FRIDAY, TRANSITIONED TO A 00Z GFS/00Z ECMWF COMPROMISE AS THEIR SOLUTIONS WITH SANDY CONVERGE. THE EXTRATROPICAL TRANSITION OF SANDY MAY HAVE ALREADY BEGUN BASED UPON RECENT SATELLITE IMAGERY...A PROCESS EXPECTED TO COMPLETE BETWEEN TUESDAY AND WEDNESDAY PER NHC. THE DETERMINISTIC GUIDANCE (PARTICULARLY THE 00Z ECMWF) SHOW PRESSURE SOLUTIONS WELL BEYOND WHAT HAS EVER BEEN OBSERVED NEAR THE NEW JERSEY/NEW YORK COAST (EVEN EXCEEDING THE 1938 LONG ISLAND EXPRESS HURRICANE) EARLY IN THE MEDIUM RANGE PERIOD. THE DETERMINISTIC GUIDANCE (CANADIAN, GFS, AND ECMWF INCLUDED) HAS SHOWN A VERY STRONG BIAS WITH TROPICAL CYCLONES GAINING LATITUDE AND/OR TRANSITIONING INTO NON-TROPICAL STORMS OVER THE PAST COUPLE YEARS, INCLUDING (BUT NOT EXCLUSIVE TO) LESLIE 2012, ISAAC 2012, DEBBY 2012 IN THE WESTERN SUBTROPICAL ATLANTIC, IRENE 2011, AND IGOR 2010. EVEN THE PERFECT/HALLOWEEN STORM OF 1991 "ONLY" BOTTOMED OUT AT 972 HPA, AND THIS FORECAST WAS ALLOWED TO EXCEED THAT SYSTEM WITHOUT GOING OVERBOARD. PRESSURES FOR THE STORM WERE CAPPED AROUND 965 HPA EARLY IN THE PERIOD PRIOR TO LANDFALL, AND ALLOWED TO WEAKEN ONCE INLAND. THIS WAS COORDINATED WITH THE OCEAN PREDICTION CENTER (OPC) AND IS CLOSE TO THE PAST COUPLE DAYS OF HPC/OPC CONTINUITY. KEEP IN MIND THIS PREFERENCE WOULD INDICATE THAT THE MODEL-DERIVED QPFS FOR THE GUIDANCE SHOWING CENTRAL PRESSURES UNDER 965 HPA ARE LIKELY TOO EXCESSIVE DUE TO THEIR EXTREME LOW PRESSURE SOLUTIONS FOR SANDY. WEATHER IMPACTS =============== PER THIS SOLUTION, FROM SUNDAY THROUGH WEDNESDAY, WINDS NEAR HURRICANE-FORCE ARE EXPECTED TO LASH EXPOSED AREAS OF THE NORTHEAST/MID-ATLANTIC STATES (THE COAST AND TOPOGRAPHY), LEADING TO POTENTIALLY SERIOUS COASTAL EROSION AND COASTAL FLOODING. THE TIMING OF THE FULL MOON AND THE BUILD-UP OF TIDES OVER MULTIPLE TIDAL CYCLES SHOULD EXACERBATE THE SITUATION ALONG THE COAST, PARTICULARLY IN CORNERS SUCH AS THE NEW YORK BIGHT. HEAVY RAINS ARE EXPECTED TO FOCUS WITHIN SANDY'S WARM CONVEYOR BELT CIRCULATION AS WELL AS ALONG ITS DRAPING WARM FRONT FROM THE NORTHERN MID-ATLANTIC STATES INTO EASTERN CANADA, WITH LOCAL AMOUNTS EXCEEDING 10 INCHES POSSIBLE. THIS SOLUTION WOULD ALLOW SIGNIFICANT SNOWS WITHIN ITS COMMA HEAD PATTERN TO FALL ACROSS THE MOUNTAINS OF WEST VIRGINIA/WESTERN PENNSYLVANIA/EASTERN OHIO; LIKELY NOT TO THE EXTREME DEGREE SEEN WITHIN ANY OF THE CURRENT DETERMINISTIC GUIDANCE. LAKE EFFECT SNOWS ACROSS THE EASTERN GREAT LAKES ARE POSSIBLE THROUGH THE PERIOD WITHIN THE CYCLONIC FLOW IN THE SYSTEM'S COLD SECTOR. AS THE CYCLONE WEAKENS AS IT PULLS NORTHWARD THURSDAY INTO NEXT FRIDAY, WINDS SHOULD SLACKEN AS SHOULD PRECIPITATION AMOUNTS/COVERAGE ACROSS THE NORTHEAST. ROTH |