WDXS31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (TWENTYFOUR) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1S 83.9E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 763 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 24S WITH A MORE ORGANIZED, BUT STILL BROAD, WIND FIELD AND
CENTRALIZED CONVECTION FORMING OVER THE CENTER OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC). ENVIRONMENTAL ANALYSIS INDICATES THAT
24S IS IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD
OUTFLOW, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA
SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE ANIMATED EIR IMAGERY. THE INITIAL INTENSITY
OF 40 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY
DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.
ADDITIONALLY, A PARTIAL 081550Z ASCAT-C IMAGE REVEALED A LARGE AREA
OF 35 KTS WITHIN THE SOUTHERN SEMICIRCLE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   FMEE: T3.0 - 45 KTS
   CIMSS SATCON: 34 KTS AT 081900Z
   CIMSS ADT: 33 KTS AT 081800Z
   CIMSS AIDT: 32 KTS AT 081800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT ALONG THE NORTHERN
PORTION OF THE VORTEX.

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: TC 24S IS FORECAST TO TRACK
SOUTH-SOUTHWESTWARD, ALONG THE WESTERN PERIPHERY OF THE STR THROUGH
TAU 48. NEAR TAU 48, A SECONDARY STR WILL BUILD TO THE SOUTH OF THE
SYSTEM, DRIVING IT WESTWARD THROUGH TAU 96. AFTER TAU 96, THE
SYSTEM WILL BEGIN TO ROUND THE RIDGE AND TAKE A MORE SOUTHWESTWARD
TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING
INTENSITY, TC 24S IS FORECAST TO MARGINALLY INTENSIFY THROUGH TAU
36. DRY AIR WITHIN THE NORTHERN SEMICIRCLE WILL BE THE MAIN CULPRIT
FOR THE LIMITED INTENSIFICATION DURING THIS TIME. NEAR TAU 48,
VERTICAL WIND SHEAR IS EXPECTED TO RISE ABOVE 25 KTS AND WILL
PERSIST THROUGH THE REMAINDER OF THE FORECAST. THIS WILL CAUSE 24S
TO WEAKEN, WITH DISSIPATION FORECAST TO OCCUR AROUND TAU 120.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 24S WITH A GRADUALLY INCREASING CROSS-TRACK
SPREAD TO 225 NM AT TAU 120 AND NO SIGNIFICANT OUTLIERS. THE JTWC
TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE THROUGH TAU 72 AND
MEDIUM THEREAFTER. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT WITH
A PRIMARY OUTLIER BEING COAMPS-TC, WHICH DOES NOT CALL FOR A
WEAKENING TREND AFTER TAU 48. THE REMAINDER OF GUIDANCE SHOWS
WEAKENING AFTER TAU 48, WITH HAFS-A BEING THE QUICKEST TO DISSIPATE
THE SYSTEM. OVERALL, THE JTWC INTENSITY FORECAST IS PLACED WITH
MEDIUM CONFIDENCE.

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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