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| #459056 (Received by flhurricane at: 5:00 AM 13.Sep.2011) TCDAT4 TROPICAL STORM MARIA DISCUSSION NUMBER 27 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142011 500 AM AST TUE SEP 13 2011 THE OVERALL CONVECTIVE ORGANIZATION OF MARIA HAS CHANGED LITTLE OVERNIGHT. NORTHWESTERLY VERTICAL WIND SHEAR AND DRY AIR INTRUSIONS INTO THE WESTERN SEMICIRCLE OF THE CYCLONE CONTINUE TO INHIBIT THE DEVELOPMENT PROCESS. UPPER-LEVEL OUTFLOW IS EXCELLENT IN THE EASTERN SEMICIRCLE...BUT IS RESTRICTED TO THE NORTHWEST...ALBEIT HAVING IMPROVED SLIGHTLY DURING THE PAST FEW HOURS. THE INITIAL INTENSITY REMAINS AT 45 KT BASED ON SATELLITE INTENSITY ESTIMATES OF 45 KT FROM TAFB AND SAB. NIGHTTIME VISIBLE IMAGERY PLUS A 0520Z TRMM MICROWAVE OVERPASS INDICATE MULTIPLE SMALL CIRCULATIONS ROTATING AROUND THE CENTER OF A LARGER LOW-LEVEL CYCLONIC GYRE. AS A RESULT...THE INITIAL POSITION IS THE MEAN CENTER OF THE LARGER CYCLONIC ENVELOPE...WHICH MAKES THE INITIAL MOTION OF 330/04 KT SOMEWHAT UNCERTAIN. THE NORTHWESTERLY TO WESTERLY VERTICAL SHEAR IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS OR SO...WHICH SHOULD KEEP THE DEEP CONVECTION AND THE VERTICAL CIRCULATION OF MARIA DISPLACED TO THE EAST OF MOST OF THE MODEL GUIDANCE. BY 36 HOURS...MARIA IS EXPECTED TO GET CAUGHT UP IN INCREASING SOUTHWESTERLY FLOW AHEAD OF A DEEP-LAYER TROUGH THAT IS CURRENTLY PASSING THE SOUTHERN TIP OF FLORIDA AS NOTED IN WATER VAPOR IMAGERY. THE CYCLONE SHOULD GRADUALLY ACCELERATE TO THE NORTHEAST...AND BY 96 HOURS BEGIN TO MERGE WITH A LARGER EXTRATROPICAL LOW PRESSURE SYSTEM OVER THE CANADIAN MARITIMES REGION. THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE RIGHT OF THE PREVIOUS ADVISORY TRACK...AND LIES ALONG THE EASTERN EDGE OF THE GUIDANCE ENVELOPE AND FOLLOWS THE SPEED OF THE CONSENSUS MODEL TVCN. MARIA IS EXPECTED TO REMAIN UNDER UNFAVORABLE WESTERLY SHEAR CONDITIONS FOR THE NEXT 24 HOURS OR SO. HOWEVER...BY 36 HOURS... THE UPPER-LEVEL LOW JUST TO THE NORTH OF THE MARIA...THAT HAS BEEN CREATING CONDITIONS QUITE HOSTILE FOR INTENSIFICATION TO OCCUR...IS EXPECTED TO DISSIPATE. THE RESULT IS THAT THE VERTICAL SHEAR IS FORECAST TO DECREASE BELOW 10 KT AND FOR THE SHEAR DIRECTION TO BACK AROUND TO THE SOUTH-SOUTHWEST. THIS SHOULD ALLOW FOR AT LEAST SOME MODEST STRENGTHENING TO OCCUR UNTIL THE VERTICAL SHEAR INCREASES FROM THE SOUTHWEST BY AROUND 48 HOURS. AT 72 HOURS AND BEYOND...MARIA WILL BE MOVING OVER SSTS COLDER THAN 20C...WHICH SHOULD INDUCE EXTRATROPICAL TRANSITION AND GRADUAL WEAKENING. THE INTENSITY FORECAST IS A BLEND OF THE SHIPS AND LGEM INTENSITY MODELS...AND REMAINS WELL BELOW THE INTENSITY FORECASTS OF THE GLOBAL AND REGIONAL MODELS...WHICH ARE ALL FORECASTING MARIA TO BECOME A HURRICANE IN 48-72 HOURS. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 21.6N 67.7W 45 KT 50 MPH 12H 13/1800Z 22.8N 68.3W 45 KT 50 MPH 24H 14/0600Z 24.8N 68.7W 50 KT 60 MPH 36H 14/1800Z 27.5N 68.7W 55 KT 65 MPH 48H 15/0600Z 31.2N 67.9W 55 KT 65 MPH 72H 16/0600Z 39.8N 61.0W 50 KT 60 MPH 96H 17/0600Z 51.0N 45.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 120H 18/0600Z...DISSIPATED/ABSORBED $$ FORECASTER STEWART |
