WDXS31 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (TWENTYFOUR) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.9S 84.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 777 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD,
PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION, WITH TWO DISCRETE AREAS OF
DEEP CONVECTION OVER THE WESTERN AND SOUTHERN QUADRANTS. HOWEVER, A
080313Z ASCAT-C IMAGE INDICATES EXTENSIVE 35-40 KNOT WINDS OVER THE
SOUTHERN SEMICIRCLE AND A SMALLER SWATH OF 30-35 KNOT WINDS
DISPLACED TO THE NORTH. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE ASCAT-C IMAGE. ENVIRONMENTAL CONDITIONS ARE
FAVORABLE, WITH STRONG POLEWARD OUTFLOW, LOW VERTICAL WIND SHEAR,
AND WARM SST VALUES. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE ASCAT-C DATA.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   FMEE: T1.5 - 25 KTS
   CIMSS D-PRINT: 24 KTS AT 080600Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 24S IS FORECAST TO TRACK
SOUTH-SOUTHWESTWARD THROUGH TAU 48 ALONG THE NORTHWESTERN PERIPHERY
OF A DEEP-LAYER SUBTROPICAL RIDGE (STR). THE SYSTEM SHOULD STEADILY
INTENSIFY TO A PEAK INTENSITY OF 55 KNOTS DURING THIS TWO-DAY PERIOD 
DUE TO ROBUST POLEWARD OUTFLOW INTO A SUBTROPICAL JET TO THE SOUTH AND 
SOUTHEAST, WARM SST VALUES (27-29C), AND LOW-MODERATE (5-20 KNOTS) 
VERTICAL WIND SHEAR (VWS). AFTER TAU 48, THE SUBTROPICAL JET TO THE 
SOUTHEAST WILL WEAKEN AND SHIFT EAST, WITH INCREASING NORTHWESTERLY 
UPPER-LEVEL FLOW AND HIGH (25-35 KNOTS) VWS OVER THE SYSTEM. 
ADDITIONALLY, EXTENSIVE DRY AIR WILL ENTRAIN INTO THE SYSTEM RESULTING 
IN GRADUAL WEAKENING THROUGH THE REMAINDER OF THE FORECAST PERIOD.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 72, WITH A 60NM CROSS-TRACK SPREAD AT TAU 72. AFTER TAU
72, THE GUIDANCE DIVERGES SIGNIFICANTLY, WITH A 265NM CROSS-TRACK
SPREAD AT TAU 120. PROBABILISTIC GUIDANCE FROM THE GEFS AND EPS
ENSEMBLES GENERALLY REVEAL A SIMILAR SPREAD, WITH A HIGH LIKELIHOOD
OF A 40-50 KNOT PEAK INTENSITY THROUGH TAU 48.   

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