WDPN32 PGTW 092100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (BOLAVEN) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.0N 147.5E INITIAL INTENSITY: 60 KTS GEOGRAPHIC REFERENCE: 156 NM EAST-SOUTHEAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 27 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 15W (BOLAVEN) CONTINUES TO SLOWLY CONSOLIDATE AND INTENSIFY AS IT APPROACHES THE SOUTHERN MARIANAS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A PERSISTENT CENTRAL DENSE OVERCAST (CDO) FEATURE, WITH DEEP CYCLING CONVECTION. AS WE APPROACH CONVECTIVE MAXIMUM, ANOTHER FLARE UP OF DEEP CONVECTION CAN BE SEEN IN THE LATEST EIR IMAGERY WITH DISCRETE VORTICAL HOT TOWERS FIRING UP ALONG THE SOUTHERN PERIPHERY OF THE CORE, ACHIEVING CLOUD TOP TEMPERATURES AS LOW AS -92C. HOWEVER, THESE VHTS ARE STILL STRUGGLING TO WRAP UPSHEAR (TO THE NORTHEAST) AND THUS THE INNER CORE REMAINS ILL-DEFINED. THE HAFS-A POTENTIAL VORTICITY CROSS-SECTION STILL SHOWS A TILTED VORTEX, WHICH IS SUPPORTED BY ANALYSIS OF A 091746Z SSMIS PASS, WHICH SHOWS A DEVELOPING, BUT AS OF YET STILL DISORGANIZED, UPPER-LEVEL ROTATION DISPLACED TO THE SOUTHWEST OF A DEVELOPING LOW-LEVEL CENTER (LLC). VERTICAL WIND PROFILES AND THE 18Z SOUNDING FROM GUAM SHOW NORTHEASTERLY WINDS UP TO 35 KNOTS FROM ABOUT 5000 TO 30000 FEET. ANIMATED RADAR DATA FROM GUAM SHOW A DEVELOPING EYE FEATURE LURKING UNDER THE CDO, WITH A WEAK BUT STRENGTHENING EYEWALL PARTICULARLY EVIDENT ON THE WESTERN SIDE OF THE EYE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE USING THE RADAR DATA, ADJUSTED SLIGHTLY TO ACCOUNT FOR THE TILT. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AVERAGE OF THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES SUPPORTED BY THE CIMSS ADT AND DPRINT ESTIMATES. THE SYSTEM IS IN AGGREGATE MOVING NORTHWESTWARD THOUGH THE RADAR DATA SUGGESTS THAT IT IS WOBBLING OR JUMPING AS THE VORTEX CONTINUES TO ALIGN. ANALYSIS REVEALS A FAVORABLE ENVIRONMENT, WITH LOW (5-10 KNOTS) VWS, ZESTY SSTS AND MODERATE POLEWARD AND WESTWARD OUTFLOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) COMPLEX ARCING FROM NORTH TO EAST OF THE SYSTEM. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.0 - 65 KTS RJTD: T3.5 - 55 KTS KNES: T3.5 - 55 KTS CIMSS SATCON: 61 KTS AT 091546Z CIMSS ADT: 57 KTS AT 091730Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 5-10 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: VORTEX TILT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: IN THE NEAR-TERM, TS 15W IS EXPECTED TO MAKE ITS WAY GENERALLY TOWARDS THE WEST-NORTHWEST TOWARDS TINIAN AND SAIPAN ALONG THE SOUTH-SOUTHWEST SIDE OF A LARGE DEEP-LAYER RIDGE CURRENTLY CENTERED TO THE NORTH. DEVIATIONS FROM THE FORECAST TRACK ARE EXPECTED IN THE NEXT 12 HOURS AS THE VORTEX ALIGNS AND MAY APPEAR TO TRACK MORE WEST OR NORTH OVER SHORT PERIODS OF TIME. THE VORTEX IS EXPECTED TO ALIGN WITHIN THE NEXT 12 HOURS OR SO AND AT THE SAME TIME THE RIDGE CENTER TO THE NORTH WILL SHIFT RAPIDLY TO THE EAST WITH THE WESTERN PORTION OF RIDGE RAPIDLY ERODING AHEAD OF AN APPROACHING MID-LATITUDE TROUGH. AS A RESULT, THE TRACK IS EXPECTED TO TURN MORE FIRMLY NORTHWESTWARD AFTER TAU 12, INTO THE BREAK IN THE RIDGE. TS 15W WILL SLOW DOWN AFTER TAU 36 AS IT NEARS AND THEN REACHES THE RIDGE AXIS AROUND TAU 48. BY TAU 72, THE SYSTEM WILL BE NORTH OF THE RIDGE AXIS AND WILL ACCELERATE TO THE NORTHEAST THROUGH THE REMAINDER OF THE FORECAST PERIOD. WHILE ENVIRONMENTAL CONDITIONS HAVE BEEN FAVORABLE FOR THE PAST 24 HOURS, PERSISTENT VORTEX TILT AND MISALIGNMENT HAS INHIBITED THE ONSET OF RAPID INTENSIFICATION (RI). ALL AVAILABLE GUIDANCE HOWEVER SUGGESTS THIS IS ABOUT TO CHANGE. VORTEX ALIGNMENT IS ANTICIPATED IN THE NEXT 12 TO 18 HOURS, AND ONCE THIS OCCURS, THE SYSTEM WILL BEGIN TO RI, TAKING ADVANTAGE OF INCREASED POLEWARD OUTFLOW INTO THE BASE OF THE MID-LATITUDE TROUGH APPROACHING FROM THE NORTHWEST. THE SYSTEM IS EXPECTED TO PEAK AT 130 KNOTS BY TAU 48 AS IT ROUNDS THE RIDGE AXIS. WESTERLY WIND SHEAR PICKS UP DRAMATICALLY AFTER TAU 72 AS THE SYSTEM BEGINS TO INTERACT WITH THE STRONG MID-LATITUDE WESTERLIES RESULTING IN A FAIRLY RAPID WEAKENING TREND AS THE SYSTEM BEGINS TO BE SHEARED APART. TS 15W WILL BEGIN THE EARLY PHASES OF EXTRATROPICAL TRANSITION BY TAU 120 AS IT MOVES NORTH OF THE 26C ISOTHERM, AND BEGINS TO SLIDE UNDER A 200MB JET MAX. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE MEAN TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH THE BULK OF THE FORECAST. CROSS-TRACK SPREAD GRADUALLY INCREASES TO JUST 70NM BY TAU 48 AS THE SYSTEM REACHES THE RIDGE AXIS, AND EXPANDS TO 110NM BY TAU 72. ALONG-TRACK UNCERTAINTY IS MINIMAL THROUGH TAU 48, AND BEGINS TO INCREASE BY TAU 72. THE JTWC FORECAST REMAINS VERY CONSISTENT WITH THE PREVIOUS FORECAST AND REMAINS CLOSE TO THE CONSENSUS MEAN WITH HIGH CONFIDENCE THROUGH TAU 72. IN THE EXTENDED PERIOD, CROSS-TRACK SPREAD INCREASES TO NEARLY 300NM BY TAU 120, BUT MORE SIGNIFICANTLY, ALONG-TRACK SPREAD DRAMATICALLY INCREASES TO 675NM BETWEEN THE GFS (SLOW) AND ECMWF (FAST) BY THE END OF THE FORECAST PERIOD. THE LONG-RANGE JTWC FORECAST LIES JUST WEST AND SLIGHTLY FASTER THAN THE CONSENSUS MEAN, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE CONTINUES TO SHOW STEADY TO RAPID INTENSIFICATION, WITH ALL OF THE AVAILABLE RI AIDS TRIGGERING, REFLECTING THE STRONGLY FAVORABLE ENVIRONMENTAL CONDITIONS. ADDITIONALLY, THE COAMPS-TC ENSEMBLE RI PROBABILITIES NOW EXCEED 65 PERCENT IN THE TAU 36 TO TAU 60 TIMEFRAME. THE BULK OF THE GUIDANCE SHOWS THE PEAK INTENSITY BEING REACHED AT TAU 60, FOLLOWED AFTERWARD BY SLOW BUT STEADY WEAKENING AS THE SYSTEM TRACKS RAPIDLY POLEWARD. THE JTWC FORECAST LIES ON THE LOWER END OF THE GUIDANCE PACKAGE THROUGH TAU 12, THEN LIES CLOSE TO THE RI AIDS AND HAFS-A GUIDANCE TO TAU 48, THEN THE CONSENSUS MEAN THEREAFTER. CONFIDENCE IS HIGH THROUGH TAU 72, THEN MEDIUM THROUGH THE END OF THE FORECAST PERIOD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN