WDPN31 PGTW 152100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 24W (TWENTYFOUR) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 14.8N 148.8E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 176 NM EAST OF SAIPAN MOVEMENT PAST 6 HOURS: WESTWARD AT 02 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL DEPRESSION 24W MOVING VERY SLOWLY WITH A FULLY OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC) THAT IS NOW TUCKED UNDERNEATH THE NORTHEASTERN PORTION OF DEEP CONVECTION. THE OVERALL CIRCULATION REMAINS QUITE BROAD AND ELONGATED IN THE SOUTHWEST-NORTHEAST AXIS. A 151528Z GMI 89 GHZ MICROWAVE IMAGE REVEALED CURVED CONVECTIVE BANDING CONFINED TO THE SOUTHWESTERN QUADRANT WHILE THE 37 GHZ VERSION OF THE SAME PASS SHOWED A WEAK LOW EMISSIVITY REGION NEAR THE ASSESSED CENTER. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE ANIMATED EIR IMAGERY AND THE GMI PASS DUE TO THE BROAD NATURE OF THE CIRCULATION. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF THE AGENCY DVORAK AND CIMSS INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 24W IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT FROM THE NORTH, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WEAK STEERING PATTERN WITH RIDGING TO BOTH THE NORTH AND EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: NO CURRENT ESTIMATE RJTD: T1.5 - 25 KTS CIMSS SATCON: 28 KTS AT 151800Z CIMSS ADT: 29 KTS AT 151800Z CIMSS AIDT: 26 KTS AT 151800Z CIMSS D-MINT: 29 KTS AT 151617Z CIMSS D-PRINT: 28 KTS AT 151800Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD AND EQUATORWARD OTHER FACTORS: DRY AIR TO THE NORTH ANALYSIS CONFIDENCE: INITIAL POSITION: LOW INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS FORECAST IS FURTHER EAST AND TRACKS POLEWARD MORE QUICKLY AFTER TAU 72 COMPARED TO THE PREVIOUS FORECAST. FORECAST DISCUSSION: 24W IS FORECAST TO BEGIN TRACKING NORTHWARD WITHIN THE NEXT 6-12 HOURS AS AN INCOMING SHORTWAVE TROUGH PROPAGATES EASTWARD AND BREAKS DOWN THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) THAT IS CURRENTLY CENTERED TO THE NORTH-NORTHEAST OF 24W. A GENERALLY NORTHWARD TRACK IS THEN FORECAST TO PERSIST THROUGH TAU 24, PRIMARILY DRIVEN BY THE NORTHERN EXTENSION OF A NEAR EQUATORIAL RIDGE POSITIONED TO THE SOUTHEAST. NEAR TAU 24, THE SYSTEM WILL BEGIN TO INTERACT WITH THE SOUTHWESTERN PERIPHERY OF THE STR, WHICH WILL DIRECT THE VORTEX NORTHWESTWARD THROUGH TAU 96. AFTER TAU 96, 24W IS EXPECTED TO ROUND THE WESTERN EXTENT OF THE STR AND BEGIN TO ACCELERATE NORTHEASTWARD. 24W IS CURRENTLY FORECAST TO STAY EAST OF HONSHU, HOWEVER, THERE IS STILL SOME UNCERTAINTY IN THE TIMING AND TRAJECTORY OF THE NORTHEASTWARD TURN AFTER TAU 96. IF 24W STAYS ON A NORTHWESTWARD TRACK FOR LONGER THAN ANTICIPATED, IT COULD SKIRT THE COAST AND IMPACT AREAS NEAR THE KANTO PLAIN. IN TERMS OF INTENSITY, 24W IS FORECAST TO STEADILY INTENSIFY THROUGH TAU 60 AS THE VORTEX CONSOLIDATES AND POLEWARD OUTFLOW GREATLY IMPROVES. AFTER TAU 60, THE SYSTEM WILL BATTLE WITH DRY AIR ENTRAINMENT FROM THE WEST, CAUSING THE SYSTEM TO HALT THE INTENSIFICATION TREND. IF 24W IS ABLE TO CONSOLIDATE AND FORM A MORE SYMMETRIC CORE, THEN FURTHER NTENSIFICATION COULD BE POSSIBLE AS SHEAR IS EXPECTED TO REMAIN RELATIVELY LOW. AFTER TAU 96, FURTHER INTENSIFICATION IS ALSO POSSIBLE DUE TO THE SYSTEM TAPPING INTO A ROBUST POLEWARD OUTFLOW CHANNEL PROVIDED BY A STRONG JET STREAK OVER NORTHERN JAPAN. NOTABLY, THE HAFS-A MODEL SHOWS THE SYSTEM STRUGGLING TO CONSOLIDATE AND IS THEREFORE NEVER ABLE TO FULLY STAVE OFF THE DRY AIR. AS IT STANDS, 24W IS FORECAST TO MAINTAIN LOW TYPHOON-STRENGTH THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH THE EXCEPTIONS OF JGSM AND NAVGEM, WHICH ARE MUCH FURTHER EQUATORWARD THAN THE REMAINDER OF GUIDANCE. DISCOUNTING THE TWO OUTLIERS, THE CROSS-TRACK SPREAD AT TAU 72 IS MEASURED TO BE ABOUT 150 NM. AFTER TAU 72, MODELS BEGIN TO DIVERGE DUE TO DIFFERENCES IN THE TIMING AND SPEED OF THE TRACK AROUND THE RIDGE AXIS. THE EXPERIMENTAL GOOGLE DEEPMIND ENSEMBLE MEAN AND EC-AIFS ARE THE FURTHEST EAST AND QUICKER AROUND THE RIDGE WHILE THE DETERMINISTIC GFS AND ECMWF TRACKERS ARE WESTWARD AND SLOWER. THE JTWC TRACK FORECAST IS PLACED NEAR THE MODIFIED CONSENSUS THROUGH TAU 72 AND THEN CLOSER TO THE AI-BASED MODELS DUE TO THEIR STRONG PERFORMANCE IN THE RECURVING TRACK TYPE. INTENSITY GUIDANCE GENERALLY AGREES ON INTENSIFICATION THROUGH TAU 60 FOLLOWED BY A STEADY INTENSITY THROUGH TAU 120. INTERESTINGLY, GOOGLE DEEPMIND IS AMONG THE MOST AGGRESSIVE MODELS, DEPICTING A PEAK INTENSITY OF AROUND 80 KTS AT TAU 72. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN