WDPN31 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7N 155.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 544 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM
IS NOW EMBEDDED IN THE CONVERGENT OUTER BOUNDARY OF A DEEP TUTT
CELL ANCHORED TO THE NORTHWEST. THE ASSOCIATED CONVECTION IS SHEARED 
NORTHEASTWARD, PARTIALLY EXPOSING THE LOW LEVEL CIRCULATION CENTER 
(LLCC). THE TUTT CELL IS ALSO CAUSING SUBSIDENCE ALONG THE WESTERN 
FLANK OF THE SYSTEM, SUPPRESSING CONVECTIVE ACTIVITY. THE INITIAL 
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTLY EXPOSED 
LLCC IN THE EIR LOOP AND LINED UP WITH A MICROWAVE LLCC FEATURE IN
THE 131507Z AMSR2 IMAGE. THE INITIAL INTENSITY OF 30KTS IS BASED WITH
MEDIUM CONFIDENCE ON THE HIGH END OF AGENCY DVORAK ESTIMATES AND IS
CONSISTENT WITH THE 6-HR SUSTAINED CONVECTIVE SIGNATURE.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 131513Z
   CIMSS ADT: 33 KTS AT 131740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EASTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD 21W WILL CONTINUE TO TRACK POLEWARD AROUND
THE TUTT CELL UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST.
THE UNFAVORABLE ENVIRONMENT, MOSTLY CAUSED BY STRONG VWS AND
SUBSIDENCE FROM THE TUTT CELL, WILL GRADUALLY ERODE THE SYSTEM,
LEADING TO DISSIPATION BY TAU 24, AS IT GETS FULLY EMBEDDED IN THE
TUTT CELL BOUNDARY.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGHOUT
THE FORECAST DURATION. HOWEVER DUE TO THE UNCERTAINTY IN THE SPEED
OF DETERIORATION OF THE SYSTEM DUE TO HIGH VWS, THERE IS ONLY MEDIUM 
CONFIDENCE IN THE JTWC TRACK FORECAST.  


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