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| #38090 (Received by flhurricane at: 4:58 AM 07.Aug.2005) TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 11 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SUN AUG 07 2005 NIGHTTIME SATELLITE IMAGERY INDICATES THAT THE CENTER OF TROPICAL DEPRESSION NINE HAS AGAIN REFORMED TO THE NORTH OF THE PREVIOUS ADVISORY POSITION. WHILE THE CYCLONE REMAINS SHEARED...CONVECTION HAS INCREASED SIGNIFICANTLY NEAR AND EAST OF THE CENTER. SATELLITE INTENSITY ESTIMATES ARE NOW 30 KT FROM TAFB AND 25 KT FROM SAB AND AFWA...SO THE SYSTEM WILL REMAIN A 30 KT DEPRESSION. HOWEVER... THE CLOUD PATTERN IS RESEMBLING THAT OF A SHEARED TROPICAL STORM. THE INITIAL MOTION IS A RATHER UNCERTAIN 295/9. THE DEPRESSION REMAINS ON THE SOUTH SIDE OF A LOW/MID-LEVEL RIDGE...WITH A WEAKNESS IN THE RIDGE LOCATED NEAR AND SOUTHWEST OF TROPICAL STORM HARVEY. LARGE-SCALE MODELS SUGGEST SOME WEAKNESS WILL PERSIST IN THE RIDGE OVER THE WEST-CENTRAL ATLANTIC FOR SEVERAL DAYS...AS A MID-LEVEL RIDGE NORTHWEST OF THE DEPRESSION MOVES WESTWARD AND A SECOND RIDGE BUILDS NORTHEAST OF THE DEPRESSION. THIS PATTERN SHOULD PRODUCE A WEST-NORTHWESTWARD MOTION FOR THE NEXT 48-72 HR... FOLLOWED BY A GRADUAL TURN TOWARD THE NORTHWEST OR POSSIBLY NORTH THEREAFTER. TRACK GUIDANCE GENERALLY AGREES WITH THIS SCENARIO... WITH THE NOGAPS AND GFDL CALLING FOR A MORE NORTHERLY MOTION AND THE GFS A MORE WEST-NORTHWESTERLY MOTION. THE UKMET TAKES THE DEPRESSION FARTHER WEST THAN THE OTHER MODELS...BUT IT INITIALIZED THE SYSTEM TOO FAR SOUTH EVEN BEFORE THE RECENT RE-FORMATION. THE LARGE-SCALE MODELS SUGGEST THAT THE DEPRESSION MAY MOVE MORE WESTWARD FOR THE FIRST 36-48 HR. THIS IS REFLECTED IN THE NEW TRACK FORECAST...WHICH EVEN WITH THE MORE NORTHWARD INITIAL POSITION IS SIMILAR TO THE PREVIOUS FORECAST. ONE POTENTIAL PROBLEM WITH THE FORECAST TRACK IS THAT THE CENTER MAY NOT BE THROUGH RE-FORMING JUST YET. WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL TROUGH NEAR OR JUST WEST OF THE DEPRESSION AND LOTS OF MID/UPPER-LEVEL DRY AIR. THE GFS AND CANDIAN MODELS FORECAST A SURGE OF UPPER-LEVEL EASTERLIES TO DEVELOP AND REPLACE THE TROUGH WITH AN ANTICYCLONE. THE UKMET AND NOGAPS ARE LESS BULLISH ON THIS POSSIBILITY...AND SO FAR THE WATER VAPOR IMAGERY SUPPORTS CONTINUED SHEAR. GIVEN THE INCREASE IN ORGANIZATION AND GRADUALLY WARMING SE SURFACE TEMPERATURES...SLOW DEVELOPMENT IS POSSIBLE IN SPITE OF THE SHEAR...AND THIS IS REFLECTED IN THE INTENSITY FORECAST. IF THE GFS/CANADIAN UPPER-LEVEL PATTERN DOES DEVELOP...THE SYSTEM COULD GET MUCH STRONGER THAN CURRENTLY FORECAST. IT SHOULD BE NOTED THAT THE GFDL MODEL...WHICH HAS CONSISTENTLY DISSIPATED THE DEPRESSION...NOW CALLS FOR IT TO REACH HURRICANE STRENGTH IN ABOUT FOUR DAYS. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 07/0900Z 19.6N 44.7W 30 KT 12HR VT 07/1800Z 20.0N 46.3W 30 KT 24HR VT 08/0600Z 20.7N 48.4W 35 KT 36HR VT 08/1800Z 21.4N 50.2W 35 KT 48HR VT 09/0600Z 22.2N 52.0W 40 KT 72HR VT 10/0600Z 23.5N 55.0W 45 KT 96HR VT 11/0600Z 25.5N 57.5W 50 KT 120HR VT 12/0600Z 28.0N 60.0W 55 KT |
