WDPS33 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 21P (TWENTYONE) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 170.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 158 NM EAST-NORTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A
CONSOLIDATING SYSTEM WITH FRAGMENTED FORMATIVE BANDS LOOSELY
FEEDING INTO A DEEPENING AND EXPANDING CENTRAL COLD COVER THAT IS
TOTALLY OBSCURING THE LOW-LEVEL CIRCULATION (LLC). THE INITIAL
POSITION IS EXTRAPOLATED WITH LOW CONFIDENCE FROM AN IRREGULAR LLC
FEATURE IN THE 242203Z GPM 37GHZ IMAGE. THE INITIAL INTENSITY OF
45KTS IS BASED ON OVERALL ASSESSMENT OF AGENCY AND AUTOMATED
ESTIMATES AND REFLECTS THE SLIGHT 6-HR CONVECTIVE IMPROVEMENT.
ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH WARM SST, LOW VWS,
AND MODERATE DUAL OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO
THE EAST-SOUTHEAST.  


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T2.0 - 30 KTS
   PHFO: T3.5 - 55 KTS
   CIMSS ADT: 45 KTS AT 242340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 21P WILL TRACK SOUTHEASTWARD THEN EASTWARD
UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST-SOUTHEAST. THE
FAVORABLE ENVIRONMENT WILL FUEL A SLOW INTENSIFICATION TO A PEAK OF
60KTS BY TAU 48. AFTERWARD, INCREASING VWS AND COOLING SST WILL
MOSTLY CAUSE A GRADUAL EROSION OF THE SYSTEM DOWN TO 35KTS BY TAU
120.

MODEL DISCUSSION: THE AVAILABLE NUMERICAL MODELS ARE IN OVERALL
AGREEMENT WITH A SPREAD TO 88NM BY TAU 72 THEN MORE ERRATICALLY AND
WIDELY TO 429NM BY TAU 120, LENDING MEDIUM CONFIDENCE TO THE NEAR-
TO MID-TERM PORTION, THEN LOW CONFIDENCE TO THE EXTENDED PORTION OF
THE JTWC TRACK FORECAST. THERE IS ALSO MEDIUM AND LOW CONFIDENCE IN
THE INTENSITY FORECASTS TO THE RESPECTIVE PORTIONS OF THE JTWC
FORECAST TRACK. NOTABLE LEFT-OF-TRACK OUTLIERS INCLUDE UKMET, AFUM,
AND UEMN THAT RECURVE THE VORTEX EQUATORWARD AFTER TAU 72.

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