WDPN31 PGTW 191500 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W WARNING NR 04// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM 23W (BAVI) HAS INTENSIFIED SLIGHTLY WHILE ACCELERATING EAST-NORTHEASTWARD OVER THE PAST 12 HOURS. DEEP CONVECTION HAS INCREASED NEAR THE LOW LEVEL CIRCULATION CENTER (LLCC) DURING THIS PERIOD IN RESPONSE TO STRONGLY DIFFLUENT WESTERLY FLOW ALOFT. B. THE CURRENT POSITION IS BASED ON RECENT SATELLITE FIXES FROM PGTW AND RJTD. THE CURRENT INTENSITY ESTIMATE OF 40 KNOTS IS CONSISTENT WITH DVORAK T-NUMBERS OF 3.0 FROM PGTW AND 2.5 FROM RJTD. TS 23W HAS CRESTED THE SUBTROPICAL STEERING RIDGE AXIS AND IS ACCELERATING TOWARD THE BAROCLINIC ZONE TO THE NORTH. STRONG WESTERLY FLOW ALOFT HAS INCREASED BOTH POLEWARD DIFFLUENCE AND VERTICAL WIND SHEAR. 3. FORECAST REASONING A. THE OVERALL FORECAST PHILOSOPHY HAS NOT CHANGED SIGNIFI- CANTLY SINCE THE PREVIOUS ISSUANCE OF THE PROGNOSTIC REASONING MESSAGE. HOWEVER, THE TIMELINE FOR EXTRATROPICAL TRANSITION HAS BEEN DELAYED BY APPROXIMATELY 12 HOURS. B. TS 23W WILL CONTINUE ACCELERATING INTO THE MID-LATITUDE WESTERLY FLOW PATTERN OVER THE NEXT 36 HOURS. INCREASING VERTICAL WIND SHEAR, THE INTRODUCTION OF A COOLER AND DRIER AIR MASS FROM THE NORTHWEST, AND PASSAGE OVER COOLER WATER WILL INDUCE EXTRATROPICAL TRANSITION. THIS TRANSITION IS EXPECTED TO BEGIN BY TAU 12 AND BE COMPLETE BY TAU 24. TS 23W IS ENTERING A REGION OF STRONG UPPER LEVEL DIFFLUENCE ASSOCI- ATED WITH AN UPPER-LEVEL JET STREAK IN THE BAROCLINIC ZONE TO THE NORTH. FAVORABLE INTERACTION WITH THIS JET MAX AND A DEVELOPING MID-LATITUDE LOW PRESSURE AREA TO THE NORTHWEST IS EXPECTED TO INTENSIFY TS 23W AS IT COMPLETES EXTRATROPICAL TRANSITION. FORECAST TEAM: BRAVO// NNNN