WDXS31 PGTW 150900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 5.5S 78.5E INITIAL INTENSITY: 75 KTS GEOGRAPHIC REFERENCE: 370 NM EAST-NORTHEAST OF DIEGO GARCIA MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 31 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SMALL CENTRAL DENSE OVERCAST (CDO) FEATURE, WITH A WELL-DEFINED FEEDER BAND WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER (LLCC) FROM THE WEST SIDE. VORTICAL HOT TOWERS (VHTS) WITH CLOUD TOP TEMPERATURES OF -85C ARE FIRING ON THE DOWNSHEAR SIDE OF THE VORTEX, BUT AT PRESENT ARE NOT ABLE TO WRAP UPSHEAR. THE RELATIVELY SHARP EASTERN SIDE OF THE CDO AND RAGGED AND LARGER WESTERN SIDE EFFECTIVELY POINT OUT THAT THE SHEAR VECTOR IS FROM THE EAST, WITH THE CURRENT CIMSS ESTIMATE AT 15-20 KNOTS. A LACK OF RECENT MICROWAVE OR SCATTEROMETER DATA MEANS THAT CONFIDENCE IN THE INITIAL POSITION IS RELATIVELY LOW, AS THE LLCC IS OBSCURED BY THE CDO. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A CONGLOMERATION OF SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES CENTERED ON 75-80 KNOTS. ENVIRONMENTAL CONDITIONS ARE GENERALLY FAVORABLE. OUTFLOW IS STRONG TOWARDS THE WEST AND MORE MODERATE TO POLEWARD. THE MODERATE EASTERLY SHEAR HOWEVER IS SLOWING THE PACE OF CORE CONSOLIDATION AND AXISYMMERTIZATION AND THUS INHIBITING THE RATE OF INTENSIFICATION FOR NOW. THE SYSTEM IS TRACKING GENERALLY WEST-SOUTHWESTWARD ALONG THE NORTHERN SIDE OF A DEEP STEERING RIDGE TO THE SOUTH. INITIAL WIND RADII BASIS: PERSISTENCE AND SMAP DATA. CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T4.5 - 77 KTS KNES: T4.5 - 77 KTS FMEE: T4.0 - 65 KTS CIMSS SATCON: 77 KTS AT 150325Z CIMSS ADT: 79 KTS AT 150600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: LOW INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 19S (FABIEN) IS FORECAST TO CONTINUE TRACKING TOWARDS THE WEST TO SOUTHWEST ALONG THE NORTHERN SIDE OF A DEEP STR THROUGH THE MAJORITY OF THE FORECAST PERIOD. OVER THE NEXT 36 HOURS A DEEP UPPER-LEVEL TROUGH WILL MOVE IN FROM THE WEST, ERODING AND ULTIMATELY BREAKING THE STEERING RIDGE. HOWEVER, AS THE TROUGH PUSHES BY TO THE SOUTH IT IS EXPECTED TO WEAKEN AND FILL, LEAVING TC 19S TRAPPED IN A WEAK STEERING PATTERN BETWEEN A DEVELOPING NEAR EQUATORIAL RIDGE (NER) TO THE NORTHEAST WHICH EXTENDS A RIDGE POLEWARD TO THE EAST OF TC 19S, AND STRONG STR CENTERED TO THE SOUTHWEST OVER NORTHERN MADAGASCAR. IN RESPONSE TO THE CHANGE IN THE STEERING ENVIRONMENT, TC 19S WILL SLOW DOWN SHARPLY, AND BECOME NEARLY QUASI-STATIONARY TO THE SOUTHEAST OF DIEGO GARCIA THROUGH TAU 120. A GENERALIZED SLOW DRIFT TOWARDS THE SOUTHWEST IS ANTICIPATED, BUT A MEANDERING, OR LOOPING TRACK CANNOT BE DISCOUNTED AS THE STEERING PATTERN WILL BE VERY WEAK. IN TERMS OF INTENSITY, THE MOST RECENT WATER VAPOR IMAGERY SUGGESTS THAT THE DEEP CONVECTIVE ACTIVITY IS PUSHING BACK AGAINST THE SHEAR VECTOR, BUT IS DOING SO IN A PULSING MANNER WHICH HAS YET TO BE SUSTAINED FOR MORE THAN A FEW HOURS. IT IS ANTICIPATED THAT THE CONVECTIVE ACTIVITY WILL BEGIN TO WRAP UPSHEAR, PUSH BACK ON THE MODERATE EASTERLY SHEAR, AND CONCOON THE CORE WITHIN A MESOSCALE REGION OF LOW VWS. THIS WILL ALLOW FOR RAPID AXISYMMETRIZATION OF THE VORTEX AND DEVELOPMENT OF AN UPPER-LEVEL POINT SOURCE. WITH THE WARM WATERS AND MOIST ATMOSPHERE PROVIDING AMPLE ENERGY, IT IS ANTICIPATED THE TC 19S WILL RAPIDLY INTENSIFY OVER THE NEXT 24-36 HOURS, REACHING A PEAK OF 110 KNOTS BY TAU 36. AS THE SYSTEM SLOWS DOWN AND BECOMES QUASI-STATIONARY, UPWELLING INDUCED SST COOLING, ACCOMPANIED BY A REDUCTION IN UPPER-LEVEL OUTFLOW WILL LEAD TO A SLOW WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST PERIOD. MODEL DISCUSSION: TRACK GUIDANCE HAS COME INTO BETTER AGREEMENT WITH THIS RUN, WITH ALL CONSENSUS MEMBERS NOW IN AGREEMENT, AT LEAST THROUGH TAU 120, ON A SOUTHWESTWARD TRACK. SOME OF THE MODELS INCLUDING NAVGEM AND THE HWRF DO BEGIN TO TURN THE SYSTEM TO THE EAST BY TAU 120, BUT THE REMAINDER SHOW A VERY SLOW SOUTHWESTWARD OR QUASI-STATIONARY MOTION AFTER TAU 48 AND ESPECIALLY AFTER TAU 72. THE MODEL ENVELOPE HAS TIGHTENED TO A 150NM CIRCLE (ALONG AND CROSS-TRACK SPREAD ROUGHLY EQUAL) BY TAU 120. ENSEMBLE GUIDANCE SHOWS A HIGH DEGREE OF UNCERTAINTY, WITH LARGE SPREADS IN THE ENSEMBLE MEMBERS AND SIGNIFICANT DIFFERENCES BETWEEN THE ECENS AND GEFS ENSEMBLE MEANS, PARTICULARLY AFTER TAU 120. THE UNCERTAINTY OF TRACK MOTION WITH A WEAK STEERING PATTERN AND LARGE ENSEMBLE SPREAD MEANS THAT OVERALL CONFIDENCE IN THE FORECAST TRACK REMAINS LOW. INTENSITY GUIDANCE IS ALSO COMING INTO BETTER AGREEMENT, WITH ALL CONSENSUS MEMBERS INDICATING NEAR-RAPID OR RAPID INTENSIFICATION (RI) OVER THE NEXT 24-36 HOURS. ADDITIONALLY THE DTOPS, RIPA, RICN, AND RIDE RI AIDS ARE TRIGGERED, AND THE COAMPS-TC ENSEMBLE RI PROBABILITY EXCEEDS 80 PERCENT IN THE TAU 0-24 TIMEFRAME. THE JTWC FORECAST FOLLOWS THE MAJORITY OF THE RI TREND LINE BUT DEVIATES LOWER THAN THE PEAK IN RIDE (130 KTS) AND DTOPS (120 KTS). CONFIDENCE IN THE INTENSITY FORECAST IS MEDIUM AND A HIGHER PEAK INTENSITY REMAINS POSSIBLE, AS MODEL GUIDANCE STRUGGLES WITH SMALL CORE TROPICAL CYCLONES. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN