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| #536285 (Received by flhurricane at: 4:59 AM 23.Aug.2012) TCDAT5 TROPICAL DEPRESSION TEN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL102012 500 AM AST THU AUG 23 2012 DEEP CONVECTION WITH THE TROPICAL DEPRESSION CONTINUES TO BE SPORADIC THOUGH WITH QUITE COLD CLOUD TOPS. THE CENTER APPEARS TO BE NEAR THE SOUTH SIDE OF THE CONVECTION SUGGESTING THAT THE MODERATE SOUTHERLY VERTICAL SHEAR IS INHIBITING ITS DEVELOPMENT. AS A RESULT OF THE LACK OF IMPROVEMENT OF THE ORGANIZATION OF THE DEEP CONVECTION...THE DVORAK CLASSIFICATIONS FROM TAFB AND SAB REMAIN AT A 2.0...OR ABOUT 30 KT. IN CONTRAST...TWO RECENT AMSU SATELLITE PASSES SUGGEST THAT THE CYCLONE MAY BE A 35 TO 45 KT TROPICAL STORM. GIVEN THE UNIMPRESSIVE CONVECTIVE STRUCTURE...THE SYSTEM REMAINS AS A 30-KT TROPICAL DEPRESSION. A 0406Z AMSU IMAGE FROM THE NRL WEBSITE PROVIDES MODERATE CONFIDENCE IN THE INITIAL POSITION OF THE TROPICAL DEPRESSION. THE CURRENT MOTION OF THE SYSTEM CONTINUES TOWARD THE WEST-NORTHWEST...295 DEGREES...AT 14 KT...AS THE CYCLONE IS BEING ADVECTED AROUND THE SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE. THE SYSTEM SHOULD GRADUALLY TURN TOWARD THE NORTH-NORTHWEST BY DAY FIVE AS IT REACHES THE WESTERN SIDE OF THE RIDGE. THE GLOBAL AND REGIONAL TRACK GUIDANCE SHOWS RELATIVELY TIGHT CLUSTERING AND HAD LITTLE CHANGE FROM THE PREVIOUS MODEL CYCLE. THUS THE TRACK FORECAST IS NEARLY IDENTICAL TO BOTH THE LAST ADVISORY AND THE HFIP TV15 CONSENSUS. THE INTENSITY PREDICTION IS MORE PROBLEMATIC THAN THE TRACK FORECAST. THE AFOREMENTIONED MODERATE VERTICAL SHEAR IS PRIMARILY BEING INDUCED BY AN UPPER LOW LOCATED ABOUT 600 NM NORTHWEST OF THE CYCLONE. THE TROPICAL DEPRESSION AND THE UPPER LOW SHOULD GET CLOSER TOGETHER OVER THE NEXT THREE DAYS...WHICH WOULD CONTINUE MODERATE SHEAR ACROSS THE CYCLONE. ON DAYS FOUR AND FIVE...THE VERTICAL SHEAR MAY INCREASE DUE TO THE OUTFLOW OF ISAAC. MOREOVER...THE THERMODYNAMICS ARE NOT CONDUCIVE FOR MUCH INTENSIFICATION AS SOME DRY STABLE AIR ASSOCIATED WITH A SAHARAN AIR LAYER...WORKING IN CONCERT WITH THE VERTICAL SHEAR...MAY BE REACHING THE INNER CORE OF THE CYCLONE DURING THE NEXT TWO TO THREE DAYS. THUS ONLY VERY GRADUAL INTENSIFICATION IS SHOWN THROUGHOUT THE FORECAST PERIOD IN BEST AGREEMENT WITH HWRF AND SHIPS MODELS. THE PREDICTED INTENSITIES ARE REDUCED SLIGHTLY FROM THE PREVIOUS ADVISORY. AN ALTERNATIVE SCENARIO DEPICTED BY THE ECMWF AND GFDL MODELS IS THAT THE CYCLONE COULD SUCCOMB TO THE HOSTILE ENVIRONMENT AND DISSIPATE BEFORE THE END OF THE FORECAST PERIOD. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 14.5N 40.6W 30 KT 35 MPH 12H 23/1800Z 15.2N 42.5W 35 KT 40 MPH 24H 24/0600Z 16.2N 45.0W 35 KT 40 MPH 36H 24/1800Z 17.4N 47.7W 35 KT 40 MPH 48H 25/0600Z 18.8N 50.8W 35 KT 40 MPH 72H 26/0600Z 22.0N 57.0W 40 KT 45 MPH 96H 27/0600Z 27.0N 63.0W 45 KT 50 MPH 120H 28/0600Z 31.0N 64.5W 45 KT 50 MPH $$ FORECASTER LANDSEA |
