WDXS31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 05S (DARIAN) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7S 81.9E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 886 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM
CONTINUED TO WEAKEN AS EVIDENCED BY WARMING CLOUD TOPS AND
UNRAVELING FEEDER BANDS. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A RECENTLY CLOUD-FILLED EYE FEATURE IN THE EIR
LOOP. THE INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED
ON THE AVERAGE OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND
REFLECTS THE STEADY WEAKENING. ANALYSIS INDICATES THE ENVIRONMENT
HAS BECOME UNFAVORABLE AS INCREASING VERTICAL WIND SHEAR AND
COOLING SEA SURFACE TEMPERATURE HAVE OFFSET THE STRONG POLEWARD
OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE. 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A
DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST THROUGH
SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   FMEE: T5.0 - 90 KTS
   FIMP: T4.5 - 77 KTS
   CIMSS SATCON: 87 KTS AT 270819Z
   CIMSS ADT: 75 KTS AT 271145Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 DARIAN WILL CONTINUE ON ITS CURRENT
SOUTHWESTWARD TRACK UNDER THE STEERING STR. AFTER TAU 72, IT WILL
BEGIN TO ROUND THE STR AXIS AND TURN MORE SOUTHWARD. THE
UNFAVORABLE ENVIRONMENT WILL GET WORSE AS SSTS CONTINUE TO DECREASE
AND VWS INCREASE, LEADING TO CONTINUED EROSION. BY TAU 96, THE
CYCLONE WILL BE REDUCED TO 40KTS. CONCURRENTLY BY TAU 48, THE
SYSTEM WILL APPROACH THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL
TRANSITION AND BY TAU 96, WILL TRANSFORM INTO A GALE-FORCE COLD
CORE LOW.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT,
LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST. THERE IS MEDIUM
CONFIDENCE IN THE JTWC INTENSITY FORECAST UP TO TAU 72 THEN LOW
CONFIDENCE AFTERWARD.

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