WDXS31 PGTW 110900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IVONE) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.3S 79.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 880 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 31 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SLIGHTLY
ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL CYCLONE (TC) 
24S (IVONE). STRONG (30+ KTS) NORTHWESTERLY VERTICAL WIND SHEAR (VWS) 
IS CAUSING THE DEEP CONVECTION TO TILT TOWARD THE SOUTHEAST QUADRANT 
OF THE SYSTEM. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE 
BASED ON NEARLY FULLY EXPOSED LLCC TO THE NORTHWEST OF THE DEEP 
CONVECTION. DRY AIR ORIGINATING OVER THE NORTHWESTERN SEMICIRCLE IS 
MIXING INTO THE STRATOCUMULUS CLOUD LAYER, DETERIORATING THE CORE OF 
THE TC. POLEWARD OUTFLOW REMAINS STRONG, WITH THE TAIL END OF THE JET 
TO THE SOUTH.  THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE DVORAK AGENCY FIXES, AS WELL AS THE 110305Z 
METOP-B ASCAT IMAGE SHOWING A BAND OF 40 KTS WINDS THROUGHOUT THE 
SOUTHERN PORTION OF THE WIND FIELD.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 48 KTS AT 110354Z
   CIMSS ADT: 32 KTS AT 110600Z
   CIMSS AIDT: 31 KTS AT 110500Z
   CIMSS D-MINT: 31 KTS AT 110116Z
   CIMSS D-PRINT: 31 KTS AT 110600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE NORTHWEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TC 24S IS FORECAST TO CONTINUE TRACKING
WESTWARD, UNDER THE INFLUENCE OF THE STEERING STR TO THE SOUTH. AS
THE RIDGE BUILDS AND MOVES EASTWARD, THE SYSTEM IS EXPECTED TO
FOLLOW ITS WESTERN PERIPHERY AND BEGIN TURNING SOUTHWESTWARD AROUND
TAU 24. THE SYSTEM WILL THEN ROUND THE AXIS OF THE STR BY TAU
72 AND BECOME POSITIONED UNDERNEATH THE UPPER-LEVEL WESTERLIES.
AFTER THAT, TC 24S WILL TURN SOUTHEASTWARD AND IS FORECAST TO
DISSIPATE BY TAU 96, JUST AHEAD OF AN UPPER LEVEL JET MAXIMUM. TC
IVONE IS FORECAST TO MAINTAIN INTENSITY OVER THE NEXT 48 HOURS
UNDER THE IMPACTS OF MARGINAL ENVIRONMENTAL CONDITIONS. SEA
SURFACE TEMPERATURES (SST) WILL REMAIN WARM (26-27 C), OFFSET BY THE
WEAKENING UPPER-LEVEL OUTFLOW, STRONG VWS AND CONTINUOUS DRY AIR
ENTRAINMENT. AFTER TAU 48, TC 24S WILL ENTER AN AREA OF WEAKER VWS,
OFFSET HOWEVER BY COOLING SST, LEADING TO SLIGHT WEAKENING OF THE
SYSTEM. AFTER TAU 72, THE VWS WILL START TO INCREASE AGAIN, WHICH 
COMBINED WITH SST DROPPING BELOW 25 C WILL LEAD TO THE DISSIPATION OF 
TC 24S, AS IT ALSO APPROACHES THE BAROCLINIC ZONE TO THE SOUTH.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT WITH ALL MODELS MATCHING IN REGARD TO THE STEERING MECHANISM 
AND THE RECURVING MOTION OF THE SYSTEM. CROSS-TRACK SPREAD AT TAU 72 
HOWEVER, IS OVER 230 NM, LEADING TO A MEDIUM CONFIDENCE OF THE TRACK 
ASSESSMENT. TWO MAJOR OUTLIERS ARE ECMWF AND NAVGEM ON EACH SIDE OF 
THE LONGITUDINAL SPECTRUM. EXCLUDING THE TWO MODELS FROM TRACK 
GUIDANCE NARROWS DOWN THE CROSS-TRACK SPREAD TO 130 NM AND JTWC 
FORECAST IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS WITHIN THAT 
SPREAD. LONG TERM TRACK IS ALSO ASSESSED WITH MEDIUM CONFIDENCE, AS 
THE CROSS-TRACK SPREAD REMAINS JUST ABOVE 100 NM AT TAU 96. INTENSITY 
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE THROUGHOUT THE FORECAST 
PERIOD, DRIVEN BY A DIFFERING TIMELINE OF DISSIPATION, AMONG THE
CONSENSUS MODEL MEMBERS. COAMPS-TC AND HAFS MAINTAIN 45-55
INTENSITY THROUGHOUT TAU 84 AND DISSIPATE THE SYSTEM AROUND TAU
120, WHILE GFS INDICATES WEAKENING DOWN TO 35 KTS AS SOON AS TAU
36.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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