WDPN31 PGTW 140300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (TWENTYONE) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.5N 156.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 618 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM IS
NOW TRACKING MORE POLEWARD AND REMAINS EMBEDDED IN THE CONVERGENT
OUTER BOUNDARY OF A DEEP TUTT CELL ANCHORED TO THE NORTHWEST. THE
CENTRAL CONVECTION HAS SLIGHTLY IMPROVED, LIKELY DUE TO DIURNAL
CONVECTIVE TOP COOLING. THE ASSOCIATED CONVECTION IS BEING SHEARED
NORTHWARD. 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 LOW
CLOUD TRACING INTO THE OBSCURED LOW LEVEL CIRCULATION CENTER. THE
INITIAL INTENSITY OF 35KTS IS BASED WITH MEDIUM CONFIDENCE ON THE 
HIGH END OF AGENCY DVORAK ESTIMATES AND IS CONSISTENT WITH THE 6-HR 
SUSTAINED CONVECTIVE IMPROVEMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 37 KTS AT 132103Z
   CIMSS ADT: 34 KTS AT 132340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: TS 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. A SECONDARY CIRCULATION IS FORECAST TO FORM
JUST TO THE NORTHWEST AND BECOME THE DOMINANT SYSTEM AND EVENTUALLY
ABSORB THE REMNANTS OF 21W.

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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