WDPN31 PGTW 270300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W (TWELVE) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 12.8N 178.3E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 541 NM NORTHEAST OF MAJURO MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION 12W WITH A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) AND CONVECTIVE BANDING WRAPPING AROUND THE NORTHERN SEMICIRCLE. THE WIND FIELD IS CURRENTLY ASYMMETRIC WITH THE STRONGEST WINDS TO THE NORTH AND WEAKER WINDS TO THE SOUTH OF THE LLCC. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON LOW-LEVEL CLOUD TRACING IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES RANGING FROM T1.5 TO T2.0. THE ABSENCE OF ANY RECENT MICROWAVE OR SCATTEROMETER DATA HAS CAUSED THERE TO BE SOME UNCERTAINTY IN THE CURRENT STRUCTURE OF THE SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT 12W IS IN A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) CENTERED NORTH OF WAKE ISLAND AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS PHFO: T2.0 - 30 KTS CIMSS D-PRINT: 22 KTS AT 270000Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TD 12W IS FORECAST TO TRACK WESTWARD, ALONG THE SOUTHERN PERIPHERY OF THE STR CENTERED NORTH OF WAKE ISLAND, THROUGH TAU 36. AFTERWARD A SEPARATE STR IS EXPECTED TO BUILD WEST-SOUTHWEST OF HAWAII AND WILL THEN BECOME THE PRIMARY STEERING MECHANISM THROUGH THE REMAINDER OF THE FORECAST PERIOD. AS A RESULT, 12W WILL TRACK NORTHWESTWARD THROUGH TAU 120. IN TERMS OF INTENSITY, 12W IS FORECAST TO STEADILY INTENSIFY OVER THE NEXT 24 HOURS AS THE SYSTEM CONTINUES TO SYMMETRIZE. AFTER TAU 24, THE SYSTEM IS FORECAST TO UNDERGO RAPID INTENSIFICATION (RI) UNDER THE EFFECTS OF A HIGHLY FAVORABLE ENVIRONMENT. POLEWARD OUTFLOW WILL BE ENHANCED BY A TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) CELL POSITIONED TO THE NORTH- NORTHEAST OF THE SYSTEM. VERTICAL WIND SHEAR IS EXPECTED TO STAY BELOW 10 KTS THROUGHOUT THE ENTIRE FORECAST PERIOD, PROVIDING A HIGHLY CONDUCIVE ENVIRONMENT FOR SIGNIFICANT DEVELOPMENT. CONSEQUENTLY, 12W IS FORECAST TO REACH SUPER TYPHOON STRENGTH AT AROUND 310000Z. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH A CROSS-TRACK SPREAD OF 120 NM AT THAT TIME. AFTER TAU 72, THERE BECOMES TWO NOTABLE OUTLIERS. NAVGEM, WHICH TRACKS THE VORTEX SIGNIFICANTLY FURTHER NORTH AND JGSM, WHICH TRACK THE VORTEX FURTHER SOUTH. DISREGARDING THE TWO OUTLIERS, CROSS-TRACK SPREAD REMAINS RIGHT AROUND 120 NM AT TAU 120. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MODIFIED CONSENSUS (REMOVING THE TWO OUTLIERS) WITH OVERALL HIGH CONFIDENCE. INTENSITY GUIDANCE AGREES ON RAPID DEVELOPMENT THROUGH TAU 72 AND THEN A MORE GRADUAL INTENSIFICATION THROUGH TAU 120. HAFS-A IS THE MOST AGGRESSIVE MODEL, SUGGESTING AN INTENSITY OF AROUND 150 KTS AT TAU 120 WHILE HWRF IS NEAR 115 KTS. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS, WITH MEDIUM CONFIDENCE DUE TO THE INHERENT UNCERTAINTIES REVOLVING AROUND RI. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: HIGH INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN