WDPN32 PGTW 290900MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (CHABA) WARNING NR 06//RMKS/1. FOR METEOROLOGISTS.2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (CHABA), LOCATED APPROXIMATELY 198 NM WEST-NORTHWEST OF NAVSTA GUAM, HAS TRACKED WESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS IMPROVED OVERALL CONVECTIVE STRUCTURE, WITH BANDING BEGINNING TO WRAP INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC). A 290603Z SSMIS 91 GHZ IMAGE REVEALS THE LLCC IS POSITIONED ALONG THE NORTHERN PERIPHERY OF THE DEEPEST CONVECTION, AND SUPPORTS THE CURRENT BEST TRACK POSITION WITH FAIR CONFIDENCE. THE INTENSITY IS ASSESSED AT 35 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM PGTW AND RJTD. UPPER-LEVEL ANALYSIS INDICATES A MORE FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH IMPROVING OUTFLOW AND LOW (10 TO 15 KNOTS) VERTICAL WIND SHEAR (VWS). TS CHABA IS TRACKING GENERALLY WESTWARD ALONG THE SOUTHERN PERIPHERY OF A DEEP LAYERED SUB-TROPICAL RIDGE (STR) TO THE NORTH.3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. THE STR WILL STEER TS CHABA TOWARD THE WEST-NORTHWEST WITH A GRADUAL TURN TOWARD THE NORTHWEST, AS THE UPPER-LEVEL FEATURE RE-ORIENTS. STEADY INTENSIFICATION WILL COMMENCE AS POLEWARD OUTFLFOW CONTINUES TO IMPROVE IN RESPONSE TO A WEAKENING TUTT CELL TO THE WEST OF THE SYSTEM. TS CHABA IS FORECAST TO REACH TYPHOON INTENSITY BETWEEN TAU 36 AND 48. DYNAMIC MODEL GUIDANCE REMAIN IN GOOD AGREEMENT ON THE TRACK OF THE SYSTEM IN THE NEAR TERM AND THE OFFICIAL JTWC FORECAST TRACK REMAINS NEAR THE MULTI-MODEL CONSENSUS. C. IN THE EXTENDED PERIOD, DYNAMIC MODEL GUIDANCE DIVERGES GREATLY BEYOND TAU 72, WITH THE GFS AND JGSM REMAINING ON THE RIGHT SIDE OF THE MODEL CONSENSUS, WITH THE NAVGEM AND ECMFW TO THE LEFT OF CONSENSUS. AT THIS TIME, THE OFFICIAL FORECAST TRACK REMAINS TO THE LEFT OF THE MULTI-MODEL CONSENSUS FROM TAU 72 THROUGH 120 BASED ON RUN-TO-RUN CONSISTENCY FROM THE NAVGEM AND GFS GLOBAL MODELS. THE TIMING OF THE TURN TO THE NORTH AND EVENTUAL RECURVE TOWARD THE NORTHEAST WILL DEPEND ON THE STRENGTH OF THE MID-LATITUDE TROUGH THAT IS FORECAST TO ERODE THE WESTERN PORTION OF THE STR. VWS IS FORECAST TO REMAIN LOW AND ACCOMPANIED BY FAVORABLE OUTFLOW THROUGH MOST OF THE FORECAST PERIOD, THEREFORE CONTINUED INTENSIFICATION IS FORECAST, WITH A PEAK INTENSITY OF 95 KNOTS AT TAU 96. DUE TO THE MODEL UNCERTAINTY BEYOND TAU 72, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK DURING THIS PORTION OF THE FORECAST.//NNNN
WDPN32 PGTW 291500MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (CHABA) WARNING NR 07//RMKS/1. FOR METEOROLOGISTS.2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (CHABA), LOCATED APPROXIMATELY 1011 NMSOUTHEAST OF KADENA AB, HAS TRACKED WESTWARD AT 14 KNOTS OVER THEPAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS DEEP CONVECTION INCREASING IN AREAL EXTENT, WHICH IS OBSCURING A SLOWLY-CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC). A 291153Z METOP-A 89GHZ IMAGE SHOWS CURVED CONVECTIVE BANDING OVER THE SOUTHERN SEMI-CIRCLE OF A PARTIALLY-EXPOSED LLCC WITH THE CENTER LOCATED ON THE NORTHERN EDGE OF THE DEEP CONVECTION. OVERALL, THERE IS FAIR CONFIDENCE IN THE CURRENT POSITION DUE TO THE BROAD NATURE OF THE LLCC AND LACK OF HIGH-RESOLUTION MICROWAVE IMAGERY. THE CURRENT INTENSITY IS ASSESSED AT 40 KNOTS BASED ON AN AVERAGE OF DVORAK ESTIMATES RANGING FROM T2.5 (35 KNOTS) TO T3.0 (45 KNOTS). ANIMATED WATER VAPOR IMAGERY DEPICTS IMPROVING OUTFLOW, ESPECIALLY POLEWARD OUTFLOW, WHICH IS BEING ENHANCED BY THE TUTT POSITIONED TO THE NORTHEAST. TS CHABA IS TRACKING GENERALLY WESTWARD ALONG THE SOUTHERN PERIPHERY OF A DEEP LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH.3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS 21W IS FORECAST TO INTENSIFY UNDER FAVORABLE CONDITIONS WHILE TURNING ONTO A NORTHWESTWARD TRACK ALONG THE SOUTHWEST PERIPHERY OF THE STR. DYNAMIC GUIDANCE IS IN FAIR AGREEMENT WITH A 200-NM SPREAD IN SOLUTIONS AT TAU 72. THE JTWC FORECAST IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH TAU 72. C. AFTER TAU 72, DYNAMIC GUIDANCE DIVERGES SIGNIFICANTLY WITH LARGE MODEL SPREAD AND HIGH UNCERTAINTY IN THE TIMING OF RE-CURVE AND TRACK SPEEDS. THERE ARE TWO DISTINCT CLUSTERS OF AIDS WITH NAVGEM, GFDN, COAMPS-TC AND ECMWF ON THE WESTERN SIDE OF THE AIDS ENVELOPE, AND SHOWING A MORE NORTHWARD TRACK. THE ECMWF AND NAVGEM SOLUTIONS HAVE BEEN HIGHLY ERRATIC OVER THE PAST 24 HOURS. UKMET, JENS, HWRF, GFS, AND THE GFS ENSEMBLE INDICATE A SHARP RE-CURVE SOUTH OF HONSHU, AND PROVIDE A MORE REALISTIC SOLUTION SINCE THE 200MB JET IS POSITIONED ACROSS THE KOREAN PENINSULA AND JAPAN. TS 21W IS EXPECTED TO ACCELERATE INTO THE MIDLATITUDE WESTERLIES BY TAU 120 AND WILL COMMENCE EXTRA-TROPICAL TRANSITION. DUE TO THE LARGE DEGREE OF MODEL UNCERTAINTY IN THE EXTENDED TAUS, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.//NNNN
WDPN32 PGTW 300900MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (CHABA)WARNING NR 10//RMKS/1. FOR METEOROLOGISTS.2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 21W (CHABA), LOCATED APPROXIMATELY 934 NM SOUTHEAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TS 21W IS SLOWLY CONSOLIDATING WITH IMPROVED CONVECTIVE BANDING WRAPPING INTO A MORE DEFINED BUT PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). A 300546Z AMSU 89GHZ IMAGE INDICATES THAT THE CURVED CONVECTIVE BANDING REMAINS SOMEWHAT FRAGMENTED AS THE LLCC CONTINUES TO ORGANIZE. ANIMATED WATER VAPOR IMAGERY AND CIMSS UPPER-LEVEL WIND ANALYSES CONTINUE TO REVEAL GOOD OVERALL OUTFLOW AIDED BY THE TUTT TO THE NORTH AND LOW VERTICAL WIND SHEAR. THE CURRENT POSITION AND RECENT TRACK MOTION IS BASED ON THE MSI WITH GOOD CONFIDENCE. RECENT MSI UP TO 300800Z CONTINUES TO CONFIRM THE NORTHWESTWARD TRACK MOTION, BOLSTERING CONFIDENCE THAT THE SYSTEM HAS CLEARLY MADE THE POLEWARD TRACK CHANGE. THE CURRENT INTENSITY REMAINS ASSESSED AT 50 KNOTS BASED ON AN AVERAGE OF DVORAK CURRENT INTENSITY ESTIMATES RANGING FROM T3.0 (45 KNOTS) TO T3.5 (55 KNOTS). ADDITIONALLY A 300545Z SATCON ESTIMATE OF 47 KNOTS SUPPORTS THE CURRENT INTENSITY ASSESSMENT. TS 21W IS TRACKING NORTHWESTWARD ALONG THE SOUTHWEST PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR).3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TS CHABA WILL CONTINUE TO TRACK NORTHWESTWARD ALONG THE SOUTHWEST PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE WHILE INTENSIFYING STEADILY DUE TO FAVORABLE ENVIRONMENTAL CONDITIONS. WITH THE EXCEPTION OF NAVGEM AND GFDN (TWO PRIMARY OUTLIERS), THE NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH A SPREAD OF 170-NM AT TAU 72, JUST SOUTH OF OKINAWA. THE MAIN DIFFERENCE BETWEEN NAVGEM AND THE OTHER MODELS IS THAT NAVGEM MAINTAINS AN EXTENSION OF THE STR TO THE NORTH WHILE THE MIDLATITUDE SHORTWAVE TROUGH DIGS OVER THE EAST CHINA SEA EFFECTIVELY DELAYING THE RE-CURVE. THE BULK OF THE GUIDANCE DEPICTS A MORE REALISTIC SCENARIO WITH A CLEAR BREAK IN THE STR THAT ALLOWS THE SYSTEM TO RE-CURVE. THE NAVGEM (AND GFDN) SOLUTIONS APPEAR TO BE UNLIKELY AND ARE CURRENTLY DISCOUNTED. TS 21W IS EXPECTED TO REACH A PEAK INTENSITY OF 100 KNOTS BY TAU 72. C. AFTER TAU 72, THE DYNAMIC MODELS DIVERGE SIGNIFICANTLY WITH NAVGEM AND GFDN REMAINING THE PRIMARY OUTLIERS WEST OF THE BULK OF THE NUMERICAL MODEL GUIDANCE, WHICH IS CLUSTERED NEAR OKINAWA AND WESTERN JAPAN. THE JTWC FORECAST CONTINUES TO FAVOR THE RE-CURVE SCENARIO OVER WESTERN JAPAN AS THE HIGHEST PROBABILITY SCENARIO, HOWEVER, THERE IS, OF COURSE, UNCERTAINTY IN THE EXACT TRACK NEAR OKINAWA THUS THE CURRENT FORECAST TRACK REMAINS HIGHLY CONSISTENT WITH THE PREVIOUS JTWC FORECAST TRACK. TS 21W SHOULD ACCELERATE NORTHEASTWARD AFTER TAU 96 AND IS FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION AS THE SYSTEM BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES AND ENCOUNTER INCREASING VERTICAL WIND SHEAR. LAND INTERACTION WILL ALSO SERVE TO WEAKEN THE SYSTEM RAPIDLY. OVERALL, THERE IS LOW CONFIDENCE (HIGH UNCERTAINTY) IN THE JTWC FORECAST DUE PRIMARILY TO THE LARGE MODEL SPREAD AFTER TAU 72, WHICH IS TYPICAL IN RE-CURVE SCENARIOS.//NNNN