WDPN31 PGTW 012100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 24.2N 147.6E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 782 NM SOUTHEAST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL DEPRESSION (TD) 04W WITH DEEP CONVECTION SLIGHTLY OFFSET TO THE NORTH OF A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AND A LARGE BAND OF CONVECTION ALONG THE EASTERN PERIPHERY OF THE SYSTEM. A 011026Z METOP-B ASCAT IMAGE REVEALED THE ASYMMETRIC NATURE OF THE WIND FIELD WITH THE STRONGEST WINDS (25-30 KTS) CONFINED TO THE EASTERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS INDICATES THAT 04W IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA SURFACE TEMPERATURES. THE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL THAT IS CENTERED ABOUT 300 NM TO THE SOUTHWEST OF THE SYSTEM IS CURRENTLY HINDERING THE EQUATORWARD OUTFLOW AND IS THE MAIN CAUSE OF THE SOUTHERLY VERTICAL WIND SHEAR. THE TUTT CELL IS ALSO INTRODUCING A TONGUE OF DRY AIR TO THE SOUTHERN AND SOUTHWESTERN PORTIONS OF THE CIRCULATION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON PERSISTENCE FROM THE MENTIONED ASCAT IMAGE AND AGREEMENT WITH AGENCY DVORAK FIXES. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN ELONGATED SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS DPRINT: 35 KTS AT 011800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 15-20 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: PRESSURE FROM THE TUTT CELL AND SLIGHT DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH 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 04W IS FORECAST TO CONTINUE ON A NORTH-NORTHWESTERLY TRACK ALONG THE WESTERN PERIPHERY OF THE STR THROUGH TAU 48. AFTER TAU 48, RIDGING TO THE WEST WILL BUILD AND PULL THE VORTEX TOWARD THE NORTHEAST THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING INTENSITY, 04W IS FORECAST TO STEADILY INTENSIFY TO A PEAK INTENSITY OF 55 KTS AT TAU 72 DUE TO THE OVERALL CONDUCIVE ENVIRONMENT. THE SYSTEM WILL CONTINUE TO DISTANCE ITSELF FROM THE TUTT CELL, WHICH WILL ALLOW FOR IMPROVEMENTS TO THE EQUATORWARD OUTFLOW CHANNEL AS THE SYSTEM GAINS LATITUDE. AFTER TAU 72, SEA SURFACE TEMPERATURES WILL BEGIN TO COOL, PUTTING A HALT TO FURTHER INTENSIFICATION. AND BY TAU 120, SEA TEMPERATURES ARE EXPECTED TO DROP TO AROUND 25 C, WHICH WILL INITIATE A WEAKENING TREND. ADDITIONALLY, AN UPPER-LEVEL TROUGH IS FORECAST TO PROPAGATE EASTWARD AND BEGIN INTERACTING WITH THE SYSTEM NEAR TAU 120. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH THE EXCEPTIONS OF NAVGEM AND GALWEM. NAVGEM HAS A MUCH FASTER TRACK SPEED AND GALWEM HAS THE VORTEX MAKING A SHARP EASTWARD TURN NEAR TAU 48. DISCOUNTING THE TWO OUTLIERS, THERE IS A 100 NM CROSS-TRACK SPREAD AT TAU 72. AFTER TAU 72, GFS STARTS TO BECOME AN OUTLIER AS IT ACTUALLY HAS THE VORTEX MAKING A TURN WESTWARD AFTER TAU 96 AS IT GETS CAUGHT UNDERNEATH RIDGING TO THE NORTH. THE TRACK SPEED OF THE SYSTEM WILL LIKELY DICTATE WHETHER IT WILL GET CAUGHT AND PULLED WESTWARD (SLOW) OR MOVE OFF TO THE NORTHEAST (FAST). THE JTWC TRACK FORECAST CURRENTLY HAS THE NORTHEASTWARD TRACK AS THAT IS WHAT THE MAJORITY OF CONSENSUS DEPICTS. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH MOST MODELS HAVING THE PEAK INTENSITY FROM 50-60 KTS AT TAU 84-96. COAMPS-TC (GFS BASED) SUGGESTS A HIGHER PEAK OF AROUND 85 KTS. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN