WDPN31 PGTW 080300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 22W (KROVANH) WARNING NR 028// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 30.3N 132.6E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 224 NM SOUTHEAST OF SASEBO, JAPAN MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION (TD) 22W FEATURING A FULLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AND FLARING CONVECTION IN THE NORTHWEST QUADRANT, VENTING INTO A JET STREAK OVER THE EASTERN SEA OF JAPAN. ALTHOUGH THE SYSTEM HAS TAKEN A NORTH-NORTHWESTWARD JOG OVER THE LAST SIX HOURS, IT IS EMBEDDED IN DEEP-LAYER SOUTHERLY FLOW ON THE WESTERN PERIPHERY OF A STRONG ANTICYCLONE SOUTHEAST OF HONSHU. THE ANTICYCLONIC FLOW ASSOCIATED WITH THE UPPER-LEVEL RIDGE IS ESPECIALLY STRONG, IMPARTING 20-25 KTS OF SOUTHERLY VERTICAL WIND SHEAR (VWS) OVER THE SYSTEM. TD 22W IS MOVING OVER WATERS OF 28-29 DEGREES CELSIUS, BUT THE COMBINATION OF MODERATE TO HIGH VWS AND SUBSTANTIAL DRY AIR INTRUSION INTO THE CIRCULATION RESULTS IN A LARGELY UNFAVORABLE ENVIRONMENT FOR TROPICAL DEVELOPMENT. DESPITE THESE FACTORS, TD 22W HAS NOT APPRECIABLY WEAKENED, AS EVIDENCED BY A TIMELY 072359Z BULLS-EYE ASCAT-B PASS INDICATING WINDS OF UP TO 30 KTS IN THE SOUTHEAST QUADRANT, CONSISTENT WITH THE 071158Z ASCAT-C DATA. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED LLCC IN THE MSI. THE INITIAL INTENSITY IS HELD AT 30 KTS WITH HIGH CONFIDENCE BASED ON THE RECENT SCATTEROMETER DATA. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WESTERN FLANK OF THE SUBTROPICAL RIDGE (STR) POSITIONED SOUTHEAST OF HONSHU AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T1.5 - 25 KTS CIMSS SATCON: 45 KTS AT 071940Z CIMSS ADT: 41 KTS AT 072330Z CIMSS AIDT: 40 KTS AT 072330Z CIMSS D-MINT: 31 KTS AT 072012Z CIMSS D-PRINT: 29 KTS AT 072330Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 20-25 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: NOT APPLICABLE 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TD 22W WILL CONTINUE POLEWARD ALONG THE WESTERN FLANK OF THE STR SOUTHEAST OF HONSHU THROUGH TAU 12. BY TAU 24, THE SYSTEM WILL ROUND THE NORTHWESTERN PERIPHERY OF THE RIDGE AND TURN NORTHEASTWARD AS IT INTERACTS WITH A STATIONARY FRONT NEAR THE SOUTHERN COAST OF HONSHU. THIS MOTION WILL CONTINUE UNTIL DISSIPATION BY TAU 36. WHILE TD 22W WILL TRACK OVER SUFFICIENTLY WARM WATERS PRIOR TO LANDFALL, PERSISTENT VWS AND DRY AIR INTRUSION WILL MAINTAIN AN UNFAVORABLE ENVIRONMENT FOR TROPICAL DEVELOPMENT. THESE FACTORS WOULD NORMALLY LEAD TO WEAKENING. HOWEVER, AS TD 22W CONTINUES TO GAIN LATITUDE, THE EXTENSIVE ANTICYCLONE SOUTHEAST OF HONSHU WILL SHIFT WESTWARD, TIGHTENING THE SURFACE PRESSURE GRADIENT BETWEEN THE SYSTEM AND THE RIDGE AND ENHANCING LOW-LEVEL WINDS, PARTICULARLY OVER THE EASTERN PORTION OF THE CIRCULATION. CONCURRENTLY, THE SOUTHEASTERN COASTLINE OF KYUSHU MAY ENHANCE THE COAST-PARALLEL FLOW, SUPPORTING A LOCALIZED COASTAL JET OVER THE WESTERN PORTION OF THE LLCC. THESE EFFECTS WILL SUPPORT A 30-KT INTENSITY THROUGH TAU 12. AFTER LANDFALL, TERRAIN INTERACTION OVER HONSHU WILL PROMOTE STEADY WEAKENING THROUGH DISSIPATION BY TAU 36. THEREFORE, THE JTWC INTENSITY FORECAST MAINTAINS 30 KTS THROUGH TAU 12 AND THEN WEAKENS THE SYSTEM TO DISSIPATION BY TAU 36. DESPITE THE WEAKENING TREND, LOCALIZED TERRAIN-ENHANCED WIND SPEEDS MAY OCCUR IN FAVORED COASTAL GAPS, INCLUDING THE KII CHANNEL AND WAKASA BAY. MODEL DISCUSSION: IN PRIOR MODEL RUNS, SEVERAL DYNAMICAL MODELS DEPICTED A SCENARIO IN WHICH TD 22W WOULD MAKE LANDFALL OVER WESTERN SHIKOKU AND BECOME QUASI-STATIONARY IN A WEAKER STEERING ENVIRONMENT, LEADING TO DISSIPATION. IN THE CURRENT GUIDANCE SUITE, MOST TRACKERS TURN THE SYSTEM EASTWARD AFTER TAU 12, WHILE GFS, HAFS-A, AND HWRF MAINTAIN MORE INLAND SOLUTIONS. THE AI MODELS REMAIN THE FARTHEST EAST, DEPICTING A STRONGER EASTWARD TURN THAT KEEPS THE CIRCULATION TRACKING NEARLY PARALLEL TO THE MOUNTAIN RANGES OF HONSHU. THESE DIFFERENCES RESULT IN A LARGE ALONG-TRACK SPREAD OF 370 NM AT TAU 36. THE JTWC FORECAST TRACK LIES NEAR THE CONSENSUS THROUGH TAU 12 AND THEN FOLLOWS A BLEND OF THE AI MODELS AND THE CONSENSUS. THERE REMAINS SOME SPREAD IN THE INTENSITY AIDS, WITH HAFS-A AND COAMPS-TC DEPICTING A SLIGHT INTENSIFICATION TO 35 KTS. THE JTWC INTENSITY FORECAST FOLLOWS THE WEAKENING TREND DEPICTED BY THE LOWER-END EXPERIMENTAL GOOGLE DEEPMIND SOLUTION, GIVEN THE PREDICTED EFFECTS OF PERSISTENT SHEAR, DRY AIR, AND LAND INTERACTION. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM// NNNN