WDPN31 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (MERBOK) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.9N 161.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 307 NM WEST-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM
HAS SUSTAINED ITS OVERALL CONVECTIVE SIGNATURE AND BECOME MORE
CONSOLIDATED AS IT MAINTAINED POLEWARD OUTFLOW INTO A TUTT CELL TO
THE NORTH AND THE LOW LEVEL CIRCULATION (LLC) REMAINS PARTLY
EXPOSED. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
USING LOW CLOUD TRACING IN THE MSI LOOP INTO THE PARTLY EXPOSED
LLC. THE INITIAL INTENSITY IS PLACED WITH HIGH CONFIDENCE BASED ON
OVERALL ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND 
REFLECTS THE SUSTAINED CONVECTIVE SIGNATURE. THE ENVIRONMENT IS 
FAVORABLE WITH MODERATE POLEWARD OUTFLOW AND WARM SST SLIGHTLY OFFSET 
BY LIGHT TO MODERATE VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) TO THE
SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 41 KTS AT 120224Z
   CIMSS ADT: 31 KTS AT 120220Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS MERBOK WILL CONTINUE ON ITS CURRENT TRACK
UNDER THE STEERING INFLUENCE OF THE NER UNTIL TAU 12. AFTERWARD,
THE LOW- TO MID-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST WILL 
ASSUME STEERING AND DRIVE THE CYCLONE MORE POLEWARD. AFTER TAU 48, TS 
15W WILL CREST THE STR AXIS AND ACCELERATE NORTHEASTWARD. THE 
FAVORABLE CONDITIONS WILL FUEL A STEADY INTENSIFICATION TO A PEAK OF 
85KTS BY TAU 72. AFTER TAU 48, INCREASING VWS AND COOLING SST WILL 
RAPIDLY ERODE THE SYSTEM. CONCURRENTLY BY TAU 48, IT WILL BEGIN
EXTRA-TROPICAL TRANSITION (ETT) AS IT APPROACHES THE BAROCLINIC
ZONE AND BY TAU 96, WILL COMPLETE ETT AND TRANSFORM INTO A 55KT
COLD-CORE LOW WITH AN EXPANSIVE WIND FIELD. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT,
LENDING HIGH CONFIDENCE IN THE JTWC TRACK FORECAST. THERE IS MEDIUM
CONFIDENCE IN THE INTENSITY FORECAST. 


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