WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (MERBOK) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.6N 162.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 303 NM NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE
SYSTEM HAS SIGNIFICANTLY DEEPENED AND EXPANDED AND BECAME MORE
CONSOLIDATED AS POLEWARD OUTFLOW INTO A TUTT CELL TO THE NORTH
INCREASED. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE ON
CLOSELY CLUSTERED AGENCY FIXES. THE INITIAL INTENSITY IS PLACED
WITH HIGH CONFIDENCE BASED ON A 120948 PARTIAL ASCAT PASS SHOWING
PATCHES OF 45-KT WIND BARBS ON THE NORTHEAST QUADRANT. THE
ENVIRONMENT IS FAVORABLE WITH MODERATE RADIAL 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
   RJTD: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 39 KTS AT 121130Z

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

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 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 EAST 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. AFTERWARD, 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 WITH
A GRADUAL AND EVEN SPREAD TO 250NM BY TAU 96, 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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