WDXS31 PGTW 010900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (IGGY) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1S 108.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 650 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY
COMPACT SYSTEM, WITH AN IRREGULAR CENTRAL DENSE OVERCAST (CDO)
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). DUE TO A GAP IN
MICROWAVE COVERAGE, THE INTERNAL MORPHOLOGY AND CONVECTIVE STRUCTURE 
REMAIN UNCERTAIN AT THIS TIME. HOWEVER, TWO RECENT ASCAT PASSES 
(010107Z AND 010150Z) REVEALED A VERY COMPACT AND WELL-DEFINED LLCC 
POSITIONED ON THE NORTHEASTERN EDGE OF A THE CDO. THE SCATTEROMETER 
DATA ALSO INDICATED WINDS BETWEEN 40-45 KNOTS IN THE
INNER-CORE OF THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH LOW
CONFIDENCE, BASED ON AN EXTRAPOLATION OF THE EARLIER ASCAT AND
ANALYSIS OF THE OUTER LOW-LEVEL CLOUD LINES. THE INITIAL INTENSITY
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE SCATTEROMETER DATA,
WHICH ALIGNS WELL WITH THE CIMSS ADT AND SATCON ESTIMATES.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE, CHARACTERIZED BY WARM SSTS,
LOW DEEP-LAYER VWS AND MODERATE POLEWARD OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   APRF: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 010700Z
   CIMSS ADT: 45 KTS AT 010540Z
   CIMSS AIDT: 34 KTS AT 010540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 11S (IGGY) IS CURRENTLY
TRACKING SLOWLY SOUTHEASTWARD ALONG THE SOUTHWESTERN PERIPHERY OF A
NER POSITIONED OVER BORNEO. OVER THE NEXT 24 HOURS, TC 11S WILL 
CONTINUE ITS SOUTHEASTWARD TREK, THOUGH TRACK SPEEDS WILL BEGIN TO 
DECELERATE AS THE NER PROPAGATES WESTWARD AND A SUBTROPICAL RIDGE 
(STR) BEGINS TO BUILD IN FROM THE SOUTHWEST. IN THE NEAR-TERM (24-36 
HOURS), TC 11S WILL INTENSIFY UNDER CONTINUED FAVORABLE CONDITIONS OF 
LOW VWS AND ENHANCED POLEWARD OUTFLOW AHEAD OF AN UPPER-LEVEL TROF 
PASSING BY TO THE SOUTH. THE SYSTEM IS FORECAST TO REACH A PEAK 
INTENSITY OF 60 KNOTS BY TAU 24. HOWEVER, THIS CONDUCIVE ENVIRONMENT 
WILL BE TRANSITORY. BY TAU 36, THE TROF TRANSITIONS TO THE EAST OF TC 
11S AND WILL QUICKLY INDUCE STRONG WESTERLY SHEAR ALONG WITH A VERY 
DRY MID-LEVEL AIRMASS, DECOUPLING THE VERTICAL STRUCTURE OF THE 
VORTEX. AS THE SYSTEM UNDERGOES RAPID VERTICAL SHALLOWING, THE LLCC 
WILL TURN SHARPLY WESTWARD, ALONG THE NORTHERN SIDE OF THE STR TO THE 
SOUTH WHICH WILL CONTINUE TO BUILD EASTWARD TOWARDS WESTERN 
AUSTRALIA. AS THE SYSTEM CARRIES OFF TO THE WEST, IT WILL STEADILY 
WEAKEN UNDER THE INFLUENCE OF DRY AIR AND HIGH SHEAR, DISSIPATING AS 
A TROPICAL CYCLONE NO LATER THAN TAU 72, AND LIKELY AS EARLY AS TAU 
60.   

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL
INTELLIGENCE (AI) MODELS ARE ALL IN GOOD AGREEMENT ON THE OVERALL
TRACK SCENARIO. ALL AVAILABLE GUIDANCE SHOWS THE SYSTEM REACHING
THE INFLECTION POINT AND TURNING SHARPLY WEST AT TAU 36.
CROSS-TRACK SPREAD AT THE INFLECTION POINT IS APPROXIMATELY 100NM,
BETWEEN THE ECMWF ON THE WESTERN EDGE, AND THE GFS ON THE EASTERN
SIDE OF THE TRACK ENVELOPE. BY THE END OF THE FORECAST PERIOD, THE
GFS AND ECWMF SWITCH SIDES, WITH THE GFS NOW ON THE NORTH SIDE AND
ECMWF ON THE SOUTH, BUT CROSS-TRACK SPREAD DECREASES TO APPROXIMATELY
85NM. THE AI MODELS AND THE GEFS MEAN ARE TIGHTLY PACKED NEAR THE
CONSENSUS MEAN. THE JTWC FORECAST IS POSITIONED NEAR THE EC-AIFS
AND GDM ENSEMBLE MEAN, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE
IS IN AGREEMENT ON THE OVERALL SHAPE OF THE TREND LINE, WITH A PEAK
INTENSITY OCCURRING AT TAU 24, BETWEEN 50 KNOTS (HAFS-A, CTCX AND
COTC) AND 65 KNOTS (HWRF). THE RIDE RAPID INTENSIFICATION (RI) AID
IS ALSO BEING TRIPPED, INDICATING A PEAK INTENSITY OF 85 KNOTS BY
TAU 24. THE JTWC FORECAST IS PLACED NEAR THE RI-ENHANCED CONSENSUS
MEAN WITH HIGH CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH//
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