WDPN32 PGTW 120300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (MAN-YI) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.1N 149.2E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 271 NM EAST OF NAVSTA GUAM MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 25W (MAN-YI) WITH A PARTIALY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) JUTTING OUT FROM UNDERNEATH THE BULK OF CONVECTION DISPLACED TO THE SOUTHEAST. ENVIRONMENTAL ANALYSIS INDICATES THAT 25W IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT, MODERATE (15-20 KTS) VERTICAL WIND SHEAR, DRY AIR TO THE NORTHWEST OF THE LLCC, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.5 - 35 KTS RCTP: T3.0 - 45 KTS CIMSS ADT: 47 KTS AT 120000Z CIMSS AIDT: 42 KTS AT 120000Z CIMSS DPRINT: 34 KTS AT 120000Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EQUATORWARD OTHER FACTORS: DRY AIR TO THE NORTHWEST OF THE LLCC. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: 25W IS FORECAST TO CONTINUE TRACKING GENERALLY WESTWARD THROUGH TAU 72 ALONG THE SOUTHERN PERIPHERY OF THE STR RIDGE TO THE NORTH. THE FORECAST FOR 25W IS SLIGHTLY FASTER AND MORE NORTH WHEN COMPARED TO THE PREVIOUS FORECAST, WITH PASSAGE JUST NORTH OF GUAM NEAR TAU 24. AFTER TAU 72, 25W WILL BEGIN TO TURN MORE NORTHWESTWARD AS IT TRACKS ALONG THE SOUTHWESTERN PERIPHERY OF THE STR AND HEADS TOWARD NORTHERN LUZON. REGARDING INTENSITY, 25W IS FORECAST TO GRADUALLY INTENSIFY TO AROUND 60 KTS AT TAU 48 DUE TO A CONTINUED MARGINALLY FAVORABLE ENVIRONMENT. DRY AIR AND MODERATE VERTICAL WIND SHEAR WILL INHIBIT THE DEVELOPMENT THROUGH TAU 48. HOWEVER, AFTER TAU 48, THE ENVIRONMENT IS EXPECTED TO MOISTEN AND VERTICAL WIND SHEAR DROP. AS A RESULT, 25W WILL INTENSIFY TO A PEAK OF NEAR 100 KTS AT TAU 96 AS IT ENTERS THE PHILIPPINE SEA. AFTER TAU 96, 25W WILL BEGIN TO TRACK THROUGH THE LOWER SEA SURFACE TEMPERATURE AND OHC WATERS LEFT BEHIND FROM 26W AND 27W, WHICH WILL CAUSE A WEAKENING IN INTENSITY. MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT REGARDING THE TRACK OF 25W THROUGH TAU 72 WITH A 95 NM CROSS-TRACK SPREAD AT THAT TIME. AFTER TAU 72, MODELS BEGIN TO DIVERGE WITH A CROSS-TRACK SPREAD OF 310 NM AT TAU 120 AS THE TRACK AROUND THE SOUTHWESTERN PERIPHERY OF THE STR VARIES BETWEEN MODELS. THE JTWC TRACK FORECAST IS PLACED CLOSE TO CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE CONTINUES TO BE IN POOR AGREEMENT WITH INTENSITIES RANGING FROM 40-55 KTS DURING THE TIME OF PASSAGE NEAR THE MARIANAS AND PEAK INTENSITIES RANGING FROM 100 TO 125 KTS NEAR TAU 96. THE JTWC INTENSITY FORECAST IS PLACED SLIGHTLY LOWER THAN CONSENSUS THROUGH TAU 36 DUE TO THE EXPECTED MARGINALLY FAVORABLE ENVIRONMENT TO PERSIST. PEAK INTENSITY OF 100 KTS IS PLACED SLIGHTLY LOWER THAN HAFS-A (125 KTS) AND HWRF (110 KTS) SUGGEST. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN