WDXS31 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IVONE)      
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2S 82.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1407 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN EXPOSED, 
BROAD LOW-LEVEL CIRCULATION CENTER (LLCC), WITH A SYMMETRIC REGION OF 
DEEP CONVECTION SHEARED OVER THE SOUTHERN SEMICIRCLE. DESPITE MODERATE 
TO STRONG NORTHWESTERLY VERTICAL WIND SHEAR (VWS), THE SYSTEM HAS 
MAINTAINED A ROBUST POLEWARD OUTFLOW CHANNEL WITH SHORT-LIVED PULSES 
OF WESTWARD AND NORTHWARD OUTFLOW. UNFORTUNATELY, EXTENSIVE DRY AIR 
OVER THE WESTERN AND NORTHERN SEMICIRCLES HAS CONTINUED TO HINDER 
SIGNIFICANT DEVELOPMENT. A 100417Z ASCAT-C IMAGE REVEALS AN ELONGATED 
CENTER, WITH EXTENSIVE GALE-FORCE WINDS (35-45 KNOTS) OVER THE 
SOUTHERN SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON EXTRAPOLATION FROM THE ASCAT-C IMAGE. THE INITIAL 
INTENSITY OF 45 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 
ASCAT-C IMAGE AND AN EARLIER SMOS IMAGE. THE 34-KNOT WIND RADII HAVE 
BEEN ADJUSTED TO REFLECT THE ASCAT-C DATA.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 43 KTS AT 100129Z
   CIMSS ADT: 49 KTS AT 100600Z
   CIMSS AIDT: 40 KTS AT 100500Z
   CIMSS D-PRINT: 49 KTS AT 100600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: WITHIN THE NEXT 24 HOURS, TC 24S WILL TURN
SOUTHWESTWARD THEN WESTWARD AS IT TRACKS ALONG THE BUILDING STR TO
THE SOUTH. AFTER TAU 72, THE SYSTEM WILL RECURVE SOUTHWESTWARD
AROUND THE NORTHWEST PERIPHERY OF THE STR. TC 24S IS EXPECTED TO
WEAKEN STEADILY THROUGH THE FORECAST PERIOD AS ENVIRONMENTAL
CONDITIONS DETERIORATE. OVER THE NEXT 24 HOURS, THE ROBUST POLEWARD
CHANNEL INTO THE SUBTROPICAL JET WILL CEASE, WITH THE STJ WEAKENING
AND SHIFTING EASTWARD. THE SYSTEM WILL ALSO TRACK UNDER THE LEADING
EDGE OF AN UPPER-LEVEL TROUGH, WITH INCREASING VWS (30-35 KNOTS)
AND A VERY DRY ENVIRONMENT. CONSEQUENTLY, THE SYSTEM IS FORECAST TO
DISSIPATE BY TAU 96 AS IT BEGINS TO RECURVE.    

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT, WITH A 160NM CROSS-TRACK SPREAD AT TAU 72 AND A 250NM
CROSS-TRACK SPREAD AT TAU 96. THE 100000Z GEFS AND EPS RUNS SHOW A
SIMILAR TRACK SPREAD, WITH THE BULK OF SOLUTIONS SUPPORTING THE
DISSIPATION SCENARIO. RELIABLE INTENSITY GUIDANCE ALSO SUPPORTS THE
STEADY WEAKENING TREND AND DISSIPATION SCENARIO.         

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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