WDXS31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IVONE)      
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2S 84.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1558 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 24S HAS BECOME BETTER ORGANIZED OVER THE PAST
12 HOURS AS INDICATED IN ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
(MSI), WHICH REVEALS DEEP CONVECTIVE BANDING WRAPPING AROUND A
PARTIALLY-EXPOSED, DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC). A
090344Z ASCAT-B IMAGE SHOWS A BROAD CIRCULATION CENTER WITH GALE-FORCE 
WINDS (35-40 KNOTS) PRIMARILY OVER THE EASTERN AND SOUTHERN 
SEMICIRCLES WRAPPING INTO THE WESTERN QUADRANT, WITH SIGNIFICANTLY 
WEAKER WINDS OVER THE NORTHERN QUADRANT. A 090319Z MHS 89GHZ MICROWAVE 
IMAGE DEPICTS A DEEP CONVECTIVE BAND OVER THE SOUTHERN SEMICIRCLE 
ASSOCIATED WITH THE CONVERGENT GALE-FORCE WINDS. WITH THE EXCEPTION OF 
DRY AIR ENTRAINMENT INTO THE NORTHERN QUADRANT OF THE SYSTEM, 
ENVIRONMENTAL CONDITIONS HAVE IMPROVED, WITH ROBUST POLEWARD OUTFLOW 
AND LOW VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH 
MEDIUM CONFIDENCE BASED ON THE MSI AND RECENT ASCAT IMAGE. THE INITIAL 
INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE 
PGTW AND DEMS DVORAK ESTIMATES, CONSISTENT WITH THE RECENT ASCAT DATA.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE POSITIONED
TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 090600Z
   CIMSS AIDT: 38 KTS AT 090600Z
   CIMSS D-PRINT: 27 KTS AT 090600Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 24S IS FORECAST TO TRACK
SOUTH-SOUTHWESTWARD THROUGH TAU 24 ALONG THE NORTHWESTERN PERIPHERY
OF A DEEP-LAYER SUBTROPICAL RIDGE (STR). THE SYSTEM SHOULD STEADILY
INTENSIFY TO A PEAK INTENSITY OF 50 KNOTS BY TAU 12 DUE TO THE ROBUST
POLEWARD OUTFLOW INTO A SUBTROPICAL JET TO THE SOUTH AND SOUTHEAST,
WARM SST VALUES (27-28C), AND LOW-MODERATE (5-20 KNOTS) VWS. AFTER
TAU 24, TC 24S WILL TRACK WESTWARD THROUGH TAU 72 ALONG THE NORTHERN 
PERIPHERY OF A SECONDARY STR EXPECTED TO BUILD TO THE SOUTH. 
SIGNIFICANT WEAKENING IS ANTICIPATED AS THE SUBTROPICAL JET TO THE 
SOUTHEAST WEAKENS AND SHIFTS EAST, WITH INCREASING NORTHWESTERLY 
UPPER-LEVEL FLOW AND HIGH (25-35 KNOTS) VWS OVER THE SYSTEM. AFTER TAU 
72, THE SYSTEM WILL BEGIN TO RECURVE SOUTHWESTWARD, WITH DISSIPATION 
FORECAST BY TAU 120 AS EXTENSIVE DRY AIR ENVELOPS THE SYSTEM.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 72, WITH A 190NM CROSS-TRACK SPREAD AT TAU 72. AFTER
TAU 72, THE GUIDANCE DIVERGES SIGNIFICANTLY, WITH A 290NM CROSS-TRACK 
SPREAD AT TAU 120. PROBABILISTIC GUIDANCE FROM THE GEFS AND EPS 
ENSEMBLES GENERALLY REVEAL A SIMILAR SPREAD SUPPORTING THE JTWC TRACK 
FORECAST WITH MEDIUM CONFIDENCE.  

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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