WDXS31 PGTW 190900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 26S (TWENTYSIX) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 13.4S 95.8E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 97 NM SOUTHWEST OF THE COCOS ISLANDS MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY EXPOSED, TIGHT LOW LEVEL CIRCULATION CENTER (LLCC) LURKING UNDER CONVECTIVE DEBRIS. FROM ABOUT 190300Z ONWARDS, A BURST OF CONVECTION DEVELOPED JUST WEST OF THE VORTEX CENTER AND THE LLCC BRIEFLY TUCKED UP UNDER THIS SMALL CONVECTIVE MASS. HOWEVER, BY 190700Z THE CONVECTION HAS DISSIPATED, LEAVING THE LLCC ONCE AGAIN EXPOSED AND HIGHLY TILTED WESTWARD WITH HEIGHT. CIMSS VWS ESTIMATES ARE CURRENTLY SHOWING EASTERLY SHEAR OF ABOUT 25-30 KNOTS OR EVEN SLIGHTLY HIGHER, WHICH IS CONSISTENT WITH THE SATELLITE PRESENTATION AND THE INABILITY OF THE SYSTEM TO MAINTAIN PERSISTENT CONVECTION IN AND AROUND THE INNER CORE OF THE VORTEX. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC IN THE MSI. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON PERSISTENCE WITH SCATTEROMETER AND SMOS DATA FROM ABOUT 18 HOURS AGO, AND CONSISTENT WITH THE HIGHER T3.0 DVORAK CURRENT INTENSITY ESTIMATES NOTED ABOVE. THE ENVIRONMENT IS MARGINAL AT BEST, WITH WARM SSTS AND STRONG WESTWARD OUTFLOW OFFSET BY THE HIGH VWS AND RELATIVELY DRY AIR TO THE NORTH AND EAST OF THE SYSTEM. INITIAL WIND RADII BASIS: PERSISTENCE AND PARTIAL SCATTEROMETER PASS. CURRENT STEERING MECHANISM: GENERALLY WEAK AND COMPETING STEERING PATTERN BETWEEN THE SUBTROPICAL RIDGE (STR) TO THE SOUTH AND LOW- TO MID-LEVEL WESTERLY WIND BURST FLOW TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS KNES: T2.5 - 35 KTS DEMS: T3.0 - 45 KTS APRF: T2.5 - 35 KTS CIMSS SATCON: 48 KTS AT 190640Z CIMSS ADT: 34 KTS AT 190530Z CIMSS AIDT: 31 KTS AT 190530Z CIMSS D-PRINT: 36 KTS AT 190600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 25-30 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG WESTWARD 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: TC 26S REMAINS TRAPPED BETWEEN A BELT OF LOW- TO MID-LEVEL NORTHWESTERLIES TO THE NORTH AND A DEEP-LAYER STR TO THE SOUTH. OVER THE PAST 12 HOURS OR SO, THE STR HAS BEEN THE DOMINATE INFLUENCE, AND AFTER A BRIEF SOUTHEASTWARD EXCURSION, TC 26S HAS TRACKED FOR THE MOST PART TOWARDS THE SOUTHWEST SINCE THIS MORNING. OVER THE NEXT 12 HOURS OR SO, THE STR IS EXPECTED TO WEAKEN AND SHIFT EASTWARD, WHICH WILL ALLOW THE INFLUENCE OF THE WESTERLIES TO THE NORTH TO INCREASE, AND TURN TC 26S TOWARDS THE SOUTHEAST THROUGH TAU 72. A COMBINATION OF WEAKENING MONSOON WESTERLIES TO THE NORTH AND A RESTRENGTHENING STR TO THE SOUTH WILL GENERATE A WEAK STEERING PATTERN AND THE SYSTEM IS EXPECTED TO SLOW SIGNIFICANTLY, GENERALLY BECOMING QUASI-STATIONARY AFTER TAU 72. IN TERMS OF INTENSITY, THE RECENT BURSTS OF CONVECTIVE ACTIVITY HAVE PROVIDED THE IMPETUS TO CONTINUE SPINNING UP THE LOW-LEVEL WIND FIELD AND IT IS ASSUMED THE SYSTEM HAS MAINTAINED 45 KNOT INTENSITY, AS MEASURED BY AN EARLIER SMOS PASS. HOWEVER, THE SYSTEM REMAINS HIGHLY TILTED AND IT WILL BE DIFFICULT FOR THE SYSTEM TO OVERCOME THE PERSISTENT, STRONG, EASTERLY SHEAR AND ACHIEVE SYMMETRIZATION. THE WIND FIELD HOWEVER WILL NOT WEAKEN SIGNIFICANTLY IN THE SHORT-TERM, AND THE FORECAST CALLS FOR A STEADY STATE INTENSITY THROUGH TAU 24. THEREAFTER, WHILE SHEAR IS EXPECTED TO WEAKEN SLIGHTLY, LARGE-SCALE SUBSIDENCE AND SIGNIFICANT DRYING OF THE AIRMASS ALONG THE NORTHERN SIDE OF THE CIRCULATION WILL BEGIN TO IMPACT THE SYSTEM. THE DRY AIR WILL BE INGESTED INTO THE INNER CORE OF THE SYSTEM AFTER TAU 24, RESULTING IN A SLOW BUT STEADY WEAKENING TREND THROUGH TAU 48. SOME MODEST MOISTENING AND DECREASE IN SHEAR IS EXPECTED AFTER TAU 48, THOUGH BY THAT TIME, HAVING SPENT A SIGNIFICANT AMOUNT OF TIME OVER RELATIVELY THE SAME AREA, COOL WATER UPWELLING WILL OFFSET THE OTHERWISE MORE FAVORABLE ENVIRONMENTAL CONDITIONS. THE TUG OF WAR BETWEEN THESE COMPETING INFLUENCES MEANS THE SYSTEM WILL LIKELY MAINTAIN MINIMAL TROPICAL STORM STRENGTH THROUGH THE END OF THE FORECAST PERIOD, THOUGH IT IS POSSIBLE IT COULD WEAKEN BELOW WARNING THRESHOLD PRIOR TO TAU 120. MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS COME INTO BETTER OVERALL AGREEMENT WITH THIS NEW RUN. ALL MEMBERS OF THE CONSENSUS EXCEPT NAVGEM NOW SHOW A TRACK THAT TURNS SHARPLY SOUTHWARD WITH THE NEXT SIX HOURS FOLLOWED BY A GENERAL TRACK TOWARDS THE SOUTHEAST THROUGH TAU 72. AFTER THIS POINT, THE GUIDANCE BEGINS TO FAN OUT WITH MOST MEMBERS INDICATING AN INFLECTION POINT AROUND TAU 96 WHERE THE TRACK TURNS BACK TOWARDS THE SOUTH AND WEST. AS MENTIONED, THE NAVGEM TRACKS THE SYSTEM STRAIGHT SOUTHWEST THROUGH THE FORECAST PERIOD, WHILE THE ECMWF ENSEMBLE MEAN TRACKS THE SYSTEM SOUTHWARD THEN WEST AFTER TAU 72 AND THE ECMWF AIFS LOOPS THE SYSTEM BACK NORTHWARD AFTER TAU 72. GEFS AND ECENS ENSEMBLE MEMBERS DEPICT A SQUASHED SPIDER TYPE SCENARIO, WITH MEMBERS ROUGHLY EQUALLY SPREAD OUT ACROSS A WIDE FAN OF POTENTIAL TRACKS FROM WEST TO SOUTHEAST TO EAST OR EVEN LOOPING. THE JTWC FORECAST ROUGHLY CONSISTENT WITH THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD, WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS SPLIT, WITH THE DECAY-SHIPS (BOTH GFS AND NAVGEM) SHOWING MODEST INTENSIFICATION TO 50-60 KNOTS BEFORE WEAKENING AFTER TAU 72. THE REMAINDER OF THE GUIDANCE PACKAGE SHOWS EITHER A FLAT TRACE OR SLIGHT INTENSIFICATION IN THE SHORT-TERM, FOLLOWED BY A SLOW WEAKENING THAT LEVELS OFF AROUND 35 KNOTS AFTER TAU 48. THE JTWC FORECAST IS CONSISTENT WITH THE CONSENSUS MEAN, THE HAFS AND COAMPS-TC, WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: LOW TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN