WDXS31 PGTW 050300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08S (BATSIRAI) WARNING NR 019// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 19.9S 51.3E INITIAL INTENSITY: 100 KTS GEOGRAPHIC REFERENCE: 223 NM EAST-SOUTHEAST OF ANTANANARIVO, MADAGASCAR MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 45 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT THE COLD RING AROUND THE EYE HAS WARMED SOMEWHAT OVER THE PAST 12 HOURS. A 042211Z AMSR2 MICROWAVE PASS REVEALED THAT THE NORTHERN EYEWALL HAS ERODED, AND PERIODIC DISRUPTIONS TO THE EYEWALL ARE EVIDENT IN ANIMATED EIR IMAGERY. GIVEN THE LACK OF VERTICAL SHEAR OR COLD WATER, IT SEEMS MOST LIKELY THAT THIS EROSION IS DUE TO A COMBINATION OF DOWNSLOPING FLOW ON THE EASTERN SIDE OF MADAGASCAR, ALONG WITH MID-LEVEL DRY AIR BEING ADVECTED OVER THE ISLAND AND INTO THE NORTHERN SEMICIRCLE OF THE STORM. THIS DIAGNOSIS IS SUPPORTED BY THREE-DIMENSIONAL MODEL ANALYSES. A SENTINNEL-1A SAR PASS AT 041502Z FOUND THAT THE INTENSITY WAS 105 KT AT THE TIME, SLIGHTLY BELOW THE MEAN OF SUBJECTIVE DVORAK ESTIMATES. GIVEN THE SLIGHT DEGRADATION OF THE SATELLITE PRESENTATION AND ASSOCIATED DVORAK ESTIMATES SINCE THAT TIME, THE INITIAL INTENSITY IS LOWERED TO 100 KT. INITIAL WIND RADII BASIS: SAR DATA CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T6.0 - 115 KTS CIMSS SATCON: 115 KTS AT 042124Z CIMSS ADT: 117 KTS AT 042115Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 0-5 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL CYCLONE 08S (BATSIRAI) IS EXPECTED TO MAKE LANDFALL IN SOUTHERN MADAGASCAR BETWEEN 12 AND 24 HOURS. WHILE THE ENVIRONMENT IS GENERALLY FAVORABLE, THE IMPERFECT STRUCTURE OF THE INNER CORE AND THE LIKELY ENTRAINMENT OF DRY AIR IN THE NORTHERN SEMICIRCLE SHOULD PREVENT ANY INTENSIFICATION PRIOR TO LANDFALL, AND IN FACT SLIGHT WEAKENING IS POSSIBLE GIVEN CURRENT SATELLITE TRENDS. BATSIRAI IS BEING STEERED WEST-SOUTHWESTWARD BY THE SUBTROPICAL RIDGE TO THE SOUTH, AND THIS TRACK WILL TAKE THE STORM ACROSS MADAGASCAR AND INTO THE MOZAMBIQUE CHANNEL BY 48 HOURS. THE INTENSITY WILL BE GREATLY REDUCED BY THIS TIME DUE TO THE CROSSING OF MOUNTAINOUS TERRAIN, AROUND 40 KT. AROUND THE TIME OF REEMERGENCE OVER WATER, THE SUBTROPICAL RIDGE IS EXPECTED TO WEAKEN AS AN UPPER-LEVEL TROUGH SKIRTS BY TO THE SOUTH, RESULTING IN BATSIRAI TURNING SOUTHWARD. THE CYCLONE WILL HAVE 24-48 HOURS OF TIME OVER WARM WATER BEFORE SEA SURFACE TEMPERATURES RAPIDLY DROP TO BELOW 26 DEGREES CELSIUS BY AROUND 96 HOURS. DURING THIS PERIOD, SOME REINTENSIFICATION IS LIKELY. HOWEVER, THE REINTENSIFICATION IS LIKELY TO BE MUTED DUE TO A COUPLE OF FACTORS. FIRSTLY, THE UPPER-LEVEL ANTICYCLONE IS FORECAST TO REMAIN ANCHORED EAST OF MADAGASCAR, IMPARTING MODERATE NORTHERLY SHEAR OF 15-20 KT ON THE CYCLONE. THIS IS EXPECTED TO PUSH A PREEXISTING MID-LEVEL DRY AIR MASS IN THE MOZAMBIQUE CHANNEL INTO THE NORTHERN SEMICIRCLE OF BATSIRAI, LEADING TO EROSION OF PART OF THE INNER CORE. SECONDLY, MODELS CURRENTLY AGREE THAT THE VORTEX STRUCTURE FOLLOWING THE CROSSING OF MADAGASCAR WILL BE RATHER BROAD, WHICH WOULD NOT FACILITATE RAPID INTENSIFICATION. THE JTWC FORECAST CALLS FOR A SECONDARY PEAK OF 50 KT IN 72-96 HOURS, WHICH IS SLIGHTLY ABOVE THE MULTI-MODEL CONSENSUS. AFTER 96 HOURS, AS THE CYCLONE MOVES OVER COLDER WATERS, CONVECTION IS LIKELY TO DWINDLE, LEADING TO THE ONSET OF SUBTROPICAL TRANSITION BY 120 HOURS. MODEL DISCUSSION: THE TRACK GUIDANCE IS IN TIGHT AGREEMENT THROUGH 72 HOURS, BUT SPREAD IN FORWARD SPEED INCREASES SIGNIFICANTLY THEREAFTER. THE MULTI-MODEL CONSENSUS DURING THE 72-120 HOUR PERIOD HAS ACCELERATED SINCE 12 HOURS AGO, AND THE JTWC FORECAST FOLLOWS SUIT. THE JTWC INTENSITY FORECAST IS ALSO HIGH CONFIDENCE THROUGH 72 HOURS, CLOSE TO THE MULTI-MODEL CONSENSUS, AND THEN LIES SLIGHTLY ABOVE CONSENSUS THROUGH 120 HOURS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN