WDPN33 PGTW 270900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.7N 162.3E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 291 NM WEST-SOUTHWEST OF WAKE ISLAND MOVEMENT PAST 6 HOURS: EASTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 20W WITH A HIGHLY COMPACT PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH BUILDING DEEP CONVECTION SLIGHTLY OFFSET TO THE NORTH OF THE CENTER. A 270218Z AMSR2 89 GHZ MICROWAVE IMAGE REVEALED EXPOSED LOW-LEVEL CLOUDS TIGHTLY WRAPPING INTO THE COMPACT CORE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE ASMR2 IMAGE AND ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW. THE AGENCY DVORAK FIXES OF T2.0 ARE ESTIMATED TO BE SLIGHTLY UNDERESTIMATING THE INTENSITY DUE TO THE SMALL SIZE OF THE SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT 20W IS NOW IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A NEAR EQUATORIAL RIDGE (NER) POSITIONED TO THE SOUTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS KNES: T2.0 - 30 KTS PHFO: T2.0 - 30 KTS CIMSS SATCON: 37 KTS AT 270440Z CIMSS ADT: 34 KTS AT 270540Z CIMSS AIDT: 38 KTS AT 270540Z CIMSS D-PRINT: 27 KTS AT 270540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: BINARY INTERACTION WITH TROPICAL STORM 21W (ETAU) ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: EXTENDED THE FORECAST TO 96 HOURS AND NOW CALLS FOR SUBTROPICAL TRANSITION RATHER THAN DISSIPATION OVER WATER. ALSO, THE TRACK IS FURTHER EAST THAN THE PREVIOUS FORECAST. FORECAST DISCUSSION: TS 20W IS FORECAST TO BEGIN TURNING NORTHEASTWARD WITHIN THE NEXT 24 HOURS AS THE STEERING MECHANISM TRANSITIONS TO A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. NEAR TAU 36, THE SYSTEM WILL TRACK MORE NORTHWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE STR THROUGH TAU 72. AFTER TAU 72, AN UPPER-LEVEL TROUGH IS EXPECTED TO DIG IN FROM THE NORTH AND PICK UP 20W, PULLING IT FURTHER POLEWARD. SUBTROPICAL TRANSITION IS FORECAST TO COMPLETE AT AROUND TAU 96 AFTER THE VORTEX PASSES THE 26 C SST ISOTHERM AND INTERACTS WITH THE STRONG MID-LATITUDE TROUGH. HOWEVER, THERE IS A SEPARATE SCENARIO THAT IS STILL POSSIBLE. THE OTHER SCENARIO IS THAT 20W BECOMES ABSORBED BY THE LARGER 21W TO THE NORTHEAST. THIS SCENARIO IS MORE LIKELY IF TWO THINGS OCCUR. THE FIRST BEING THAT 20W WEAKENS CONSIDERABLY OVER THE NEXT 48 HOURS, AND THE OTHER IS IF THE TRACK SPEEDS OF 21W ARE SLOWER THAN ANTICIPATED. REGARDING INTENSITY, 20W IS FORECAST TO STEADILY INTENSIFY THROUGH TAU 48 TO A PEAK OF 60 KTS. IF THE SYSTEM IS ABLE TO STABILIZE A CORE OF CONVECTION, THEN A HIGHER INTENSITY IS POSSIBLE DUE TO THE COMPACT NATURE OF THE WIND FIELD. AFTER TAU 48, WESTERLY SHEAR AND DRY AIR IS EXEPCTED TO INCREASE, CAUSING 20W TO WEAKEN AS IT TRACKS NORTHWARD. MODEL DISCUSSION: MODEL TRACK GUIDANCE CONTINUES TO BE IN POOR AGREEMENT WITH A CROSS-TRACK SPREAD OF 370 NM AT TAU 72. HOWEVER, A MORE DISCERNIBLE TRACK DIFFERENCE BETWEEN 20W AND 21W IS MUCH MORE APPARENT THIS MODEL RUN. THE ONLY TWO TRACKERS THAT JUMP TO 21W ARE NOW NAVGEM AND GALWEM, MAKING UP THE FAR WESTERN OUTLIERS. ON THE OTHER HAND, THE EXPERIMENTAL GOOGLE DEEPMIND AND THE GFS ARE THE EASTERNMOST TRACKERS. THE JTWC TRACK FORECAST IS PLACED CLOSER TO THE GOOGLE DEEPMIND ENSEMBLE MEAN WITH OVERALL LOW CONFIDENCE. INTENSITY GUIDANCE IS NOW IN EXTREMELY POOR AGREEMENT WITH MULTIPLE RAPID INTENSIFICATION (RI) AIDS TRIGGERING THIS MODEL RUN. ADDITIONALLY, THE COAMPS-TC (GFS-BASED) SHOWS A PEAK INTENSITY OF 105 KTS, WHICH ACTUALLY ALIGNS WITH THE MULTITUDE OF RI AIDS. SHIPS OUTPUT HAS A 70 PERCENT PROBABILITY OF AN INCREASE OF 55 KTS IN 48 HOURS AS WELL. HAFS-A AND THE GOOGLE DEEPMIND SHOW A PEAK INTENSITY OF 55-60 KTS AND THE JTWC INTENSITY FORECAST IS PLACED CLOSER TO THIS DEPICTION WITH VERY LOW CONFIDENCE. THERE COULD BE MAJOR CHANGES TO THE INTENSITY FORECAST FOR 20W IF RI APPEARS MORE LIKELY THAN NOT. FORECAST CONFIDENCE: TRACK 00-72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 00-72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN WDPN33 PGTW 270900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.7N 162.3E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 291 NM WEST-SOUTHWEST OF WAKE ISLAND MOVEMENT PAST 6 HOURS: EASTWARD AT 09 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM 20W WITH A HIGHLY COMPACT PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH BUILDING DEEP CONVECTION SLIGHTLY OFFSET TO THE NORTH OF THE CENTER. A 270218Z AMSR2 89 GHZ MICROWAVE IMAGE REVEALED EXPOSED LOW-LEVEL CLOUDS TIGHTLY WRAPPING INTO THE COMPACT CORE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AMSR2 IMAGE AND ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS INTENSITY ESTIMATES LISTED BELOW. THE AGENCY DVORAK FIXES OF T2.0 ARE ESTIMATED TO BE SLIGHTLY UNDERESTIMATING THE INTENSITY DUE TO THE SMALL SIZE OF THE SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT 20W IS NOW IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE TEMPERATURES. INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A NEAR EQUATORIAL RIDGE (NER) POSITIONED TO THE SOUTH AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS KNES: T2.0 - 30 KTS PHFO: T2.0 - 30 KTS CIMSS SATCON: 37 KTS AT 270440Z CIMSS ADT: 34 KTS AT 270540Z CIMSS AIDT: 38 KTS AT 270540Z CIMSS D-PRINT: 27 KTS AT 270540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: BINARY INTERACTION WITH TROPICAL STORM 21W (ETAU) ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: EXTENDED THE FORECAST TO 96 HOURS AND NOW CALLS FOR SUBTROPICAL TRANSITION RATHER THAN DISSIPATION OVER WATER. ALSO, THE TRACK IS FURTHER EAST THAN THE PREVIOUS FORECAST. FORECAST DISCUSSION: TS 20W IS FORECAST TO BEGIN TURNING NORTHEASTWARD WITHIN THE NEXT 24 HOURS AS THE STEERING MECHANISM TRANSITIONS TO A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. NEAR TAU 36, THE SYSTEM WILL TRACK MORE NORTHWARD AS IT TRACKS ALONG THE WESTERN PERIPHERY OF THE STR THROUGH TAU 72. AFTER TAU 72, AN UPPER-LEVEL TROUGH IS EXPECTED TO DIG IN FROM THE NORTH AND PICK UP 20W, PULLING IT FURTHER POLEWARD. SUBTROPICAL TRANSITION IS FORECAST TO COMPLETE AT AROUND TAU 96 AFTER THE VORTEX PASSES THE 26 C SST ISOTHERM AND INTERACTS WITH THE STRONG MID-LATITUDE TROUGH. HOWEVER, THERE IS A SEPARATE SCENARIO THAT IS STILL POSSIBLE. THE OTHER SCENARIO IS THAT 20W BECOMES ABSORBED BY THE LARGER 21W TO THE NORTHEAST. THIS SCENARIO IS MORE LIKELY IF TWO THINGS OCCUR. THE FIRST BEING THAT 20W WEAKENS CONSIDERABLY OVER THE NEXT 48 HOURS, AND THE OTHER IS IF THE TRACK SPEEDS OF 21W ARE SLOWER THAN ANTICIPATED. REGARDING INTENSITY, 20W IS FORECAST TO STEADILY INTENSIFY THROUGH TAU 48 TO A PEAK OF 60 KTS. IF THE SYSTEM IS ABLE TO STABILIZE A CORE OF CONVECTION, THEN A HIGHER INTENSITY IS POSSIBLE DUE TO THE COMPACT NATURE OF THE WIND FIELD. AFTER TAU 48, WESTERLY SHEAR AND DRY AIR IS EXEPCTED TO INCREASE, CAUSING 20W TO WEAKEN AS IT TRACKS NORTHWARD. MODEL DISCUSSION: MODEL TRACK GUIDANCE CONTINUES TO BE IN POOR AGREEMENT WITH A CROSS-TRACK SPREAD OF 370 NM AT TAU 72. HOWEVER, A MORE DISCERNIBLE TRACK DIFFERENCE BETWEEN 20W AND 21W IS MUCH MORE APPARENT THIS MODEL RUN. THE ONLY TWO TRACKERS THAT JUMP TO 21W ARE NOW NAVGEM AND GALWEM, MAKING UP THE FAR WESTERN OUTLIERS. ON THE OTHER HAND, THE EXPERIMENTAL GOOGLE DEEPMIND AND THE GFS ARE THE EASTERNMOST TRACKERS. THE JTWC TRACK FORECAST IS PLACED CLOSER TO THE GOOGLE DEEPMIND ENSEMBLE MEAN WITH OVERALL LOW CONFIDENCE. INTENSITY GUIDANCE IS NOW IN EXTREMELY POOR AGREEMENT WITH MULTIPLE RAPID INTENSIFICATION (RI) AIDS TRIGGERING THIS MODEL RUN. ADDITIONALLY, THE COAMPS-TC (GFS-BASED) SHOWS A PEAK INTENSITY OF 105 KTS, WHICH ACTUALLY ALIGNS WITH THE MULTITUDE OF RI AIDS. SHIPS OUTPUT HAS A 70 PERCENT PROBABILITY OF AN INCREASE OF 55 KTS IN 48 HOURS AS WELL. HAFS-A AND GOOGLE DEEPMIND SHOWS A PEAK INTENSITY OF 55-60 KTS AND THE JTWC INTENSITY FORECAST IS PLACED CLOSER TO THIS DEPICTION WITH VERY LOW CONFIDENCE. THERE COULD BE MAJOR CHANGES TO THE INTENSITY FORECAST FOR 20W IF RI APPEARS MORE LIKELY THAN NOT. FORECAST CONFIDENCE: TRACK 00-72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 00-72 HR: LOW INTENSITY 72-120 HR: LOW// NNNN