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| #111289 (Received by flhurricane at: 11:00 PM 16.Sep.2006) TCDAT3 HURRICANE HELENE DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 PM EDT SAT SEP 16 2006 THE INITIAL MOTION ESTIMATE IS 300/09 KT...DESPITE A SHORT TERM MOTION OF 290/09 BETWEEN 18Z AND 00Z. THE LATTER MOTION IS BELIEVED TO BE A SHORT TERM WOBBLE AS THE CENTER REORGANIZES WITHIN THE DEEP CONVECTION. THE MODELS REMAIN IN EXCELLENT AGREEMENT ON HELENE MOVING WEST-NORTHWEST TO NORTHWESTWARD FOR THE NEXT 36-48 HOURS TOWARD A WEAKNESS IN THE SUBTROPICAL RIDGE...AND THEN MAKE A SLIGHT WESTWARD BEND IN 48-72 HOURS. AFTER THAT...THE MODELS DIVERGE QUITE SIGNIFICANTLY WITH THE GFDL...UKMET...CANADIAN...AND NOGAPS MODEL TAKING HELENE NORTHWARD...WHEREAS THE GFS...GFS ENSEMBLE...THE BAMS...AND THE STATISTICAL-DYNAMICAL MODELS KEEP THE HURRICANE ON A MORE WESTWARD COURSE AS A MID-LEVEL RIDGE BUILDS TO THE NORTH AND NORTHWEST OF HELENE OFF THE U.S. MID-ATLANTIC COAST BY DAY 5. WATER VAPOR IMAGERY AND 00Z UPPER-AIR DATA INDICATE THE UPPER-LOW THAT HAS RECENTLY MOVED OFF THE U.S. MID-ATLANTIC COAST HAS BEEN MOVING EASTWARD SIMILAR TO THE GFS SOLUTION...RATHER THAN DIGGING SOUTHEASTWARD TOWARD BERMUDA AS FORECAST BY THE OTHER MODELS. WITH THE STRONGEST WINDS NOW INDICATED BY WATER VAPOR IMAGERY AND UPPER-AIR DATA TO BE ON THE SOUTH AND EAST SIDE OF THE UPPER-LOW... THE 18Z GFS RUN MAY BE INDICATING A SIGNIFICANT CHANGE IN THE MODEL FORECAST TRACKS COULD BE FORTHCOMING. HOWEVER...UNTIL THE OTHER MODELS MAKE A CHANGE SIMILAR TO THE GFS...THE OFFICIAL TRACK WAS ONLY NUDGED SLIGHTLY WESTWARD...BASED MAINLY ON THE MORE SOUTHERLY INITIAL POSITION...AND IS SIMILAR TO BUT A LITTLE SLOWER THAN THE NHC MODEL CONSENSUS AT 96 AND 120 HOURS. AN EARLIER WINDSAT MICROWAVE OVERPASS INDICATED HELENE POSSESSED A WELL DEVELOPED LOW-LEVEL EYE FEATURE. SINCE THEN...THE RAGGED EYE FEATURE NOTED PREVIOUSLY IN CONVENTIONAL SATELLITE IMAGERY HAS ERODED...ALTHOUGH THE PAST COUPLE OF IMAGES SUGGEST THAT A BANDING EYE FEATURE MAY BE FORMING. THE INITIAL INTENSITY WAS INCREASED TO 70 KT BASED ON A BLEND OF SATELLITE ESTIMATES FROM TAFB AND SAB. ONLY SLOW INTENSIFICATION IS EXPECTED AS HELENE CONTINUES TO BATTLE PERIODIC INTRUSIONS OF DRY AIR. THE UPPER-LEVEL FLOW PATTERN AND UPSTREAM SSTS FAVORS MORE SIGNIFICANT INTENSIFICATION...BUT IT IS TOO DIFFICULT TO PREDICT AT THIS TIME JUST WHEN AND IF HELENE WILL EVENTUALLY OVERCOME THE EFFECTS OF THE MID-LEVEL DRY AIR. FORECAST POSITIONS AND MAX WINDS INITIAL 17/0300Z 19.5N 47.5W 70 KT 12HR VT 17/1200Z 20.2N 48.5W 75 KT 24HR VT 18/0000Z 21.2N 49.7W 80 KT 36HR VT 18/1200Z 22.1N 50.8W 85 KT 48HR VT 19/0000Z 22.9N 52.3W 90 KT 72HR VT 20/0000Z 24.1N 55.0W 90 KT 96HR VT 21/0000Z 26.0N 57.0W 85 KT 120HR VT 22/0000Z 29.0N 58.5W 80 KT $$ FORECASTER STEWART |
