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| #110772 (Received by flhurricane at: 4:52 AM 14.Sep.2006) TCDAT3 TROPICAL STORM HELENE DISCUSSION NUMBER 8 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 500 AM EDT THU SEP 14 2006 HELENE REMAINS A FAIRLY DISORGANIZED TROPICAL STORM. THE CONVECTIVE BAND SEEN LAST NIGHT IN THE NORTHWESTERN QUADRANT HAS SPREAD OUT AND FRAGMENTED...THERE IS LITTLE OR NO DEEP CONVECTION WITHIN ABOUT 60 N MI OF THE LOW-LEVEL CENTER...AND IN GENERAL THE CLOUD TOPS HAVE WARMED OVERNIGHT. DVORAK T-NUMBERS ARE UNCHANGED AND THE ADVISORY INTENSITY REMAINS 35 KT. THE STORM CONTINUES TO RACE WESTWARD AT 280/19 AS IT CURRENTLY LIES SOUTH OF THE CORE OF THE SUBTROPICAL RIDGE. THE SPREAD IN THE TRACK GUIDANCE HAS BECOME RELATIVELY LARGE WITH THE MODELS FALLING INTO TWO MAIN CAMPS. THE GFS...ITS ENSEMBLE MEAN...AND THE GFDL FORECAST THE RIDGE TO THE NORTH TO WEAKEN QUITE RAPIDLY AND ALLOW THE STORM TO TURN NORTHWESTWARD IN ABOUT 12 HOURS. THE UKMET AND NOGAPS MAINTAIN THE RIDGE LONGER AND FORECAST HELENE TO MAINTAIN A WEST-NORTHWESTWARD MOTION FOR ABOUT 48 MORE HOURS. ALL OF THE MODELS FORECAST A NORTHWESTWARD MOTION...AT ABOUT HALF THE CURRENT FORWARD SPEED...OVER THE CENTRAL ATLANTIC DURING DAYS 3-5. BY THAT TIME...HOWEVER...THE TRACK GUIDANCE ENVELOPE IS MORE THAN 300 MILES WIDE...SO THE TRACK FORECAST AT THOSE LONG RANGES IS QUITE UNCERTAIN. THE NEW OFFICIAL TRACK FORECAST IS MOVED TO THE LEFT OF THE PREVIOUS ADVISORY...BUT NOT AS FAR AS THE MODEL CONSENSUS. HELENE CONTINUES IN ITS STRUGGLE TO INTENSIFY...PROBABLY BECAUSE OF ITS LARGE SIZE AND THE FAST FORWARD MOTION. IT IS ASSUMED THAT THE CONVECTION WILL SOON CONSOLIDATE NEAR THE CIRCULATION CENTER AND ALLOW FOR MORE STEADY STRENGTHENING DURING THE NEXT DAY OR TWO. THE IMPACTS OF THE NEARBY SAHARAN AIR LAYER ARE UNCERTAIN BUT COULD END UP BEING AN ADDITIONAL INHIBITING FACTOR. LATER IN THE FORECAST PERIOD...SINCE THE SSTS ALONG THE FORECAST TRACK WILL REMAIN 27-28 CELSIUS AND THE GLOBAL MODELS INDICATE A WEAK SHEAR ENVIRONMENT...ALL OF THE INTENSITY GUIDANCE ANTICIPATES HELENE TO BECOME A HURRICANE. THE SHIPS MODEL HAS BACKED OFF A BIT AND NOW MAKES HELENE NO STRONGER THAN ABOUT 85 KT THROUGH FIVE DAYS...WHICH IS CLOSE TO THE LATEST GFDL SOLUTION. THE OFFICIAL FORECAST IS ADJUSTED SLIGHTLY DOWNWARD TO BE IN AGREEMENT WITH THE GUIDANCE AT THE LONGER RANGES...BUT IT IS BELOW SHIPS DURING THE FIRST 48 HOURS OR SO. FORECAST POSITIONS AND MAX WINDS INITIAL 14/0900Z 13.7N 34.7W 35 KT 12HR VT 14/1800Z 14.1N 37.0W 40 KT 24HR VT 15/0600Z 15.2N 39.6W 50 KT 36HR VT 15/1800Z 16.5N 41.6W 60 KT 48HR VT 16/0600Z 17.8N 43.0W 70 KT 72HR VT 17/0600Z 20.0N 45.5W 80 KT 96HR VT 18/0600Z 22.0N 48.5W 85 KT 120HR VT 19/0600Z 24.0N 51.0W 85 KT $$ FORECASTER KNABB |
