Tropical Storm MERBOK Advisory Sa, 10.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 20.9N 159.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 377 NM EAST-SOUTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
LOW-LEVEL CLOUD LINES WRAPPING INTO A PARTIALLY-EXPOSED, DEFINED
LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH IS POSITIONED ALONG THE
NORTHERN EDGE OF FORMATIVE CONVECTIVE BANDING. A 101809Z SSMIS
91GHZ COLOR COMPOSITE MICROWAVE IMAGE SHOWS SHALLOW BANDING
WRAPPING INTO THE LLCC WITH DEEP CONVECTIVE BANDING WRAPPING INTO
THE SOUTHEAST QUADRANT. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE SSMIS IMAGE. THE INITIAL INTENSITY OF 30
KTS IS ASSESSED WITH MEDIUM CONFIDENCE AND IS HEDGED ABOVE THE PGTW
DVORAK ESTIMATE BASED ON THE IMPROVED CONVECTIVE STRUCTURE EVIDENT
IN THE SSMIS IMAGE. UPPER-LEVEL CONDITIONS ARE COMPLEX AND
MARGINALLY-FAVORABLE WITH THE TUTT EXTENDING FROM A TUTT CELL NEAR
30N 170E TO JUST NORTH OF THE SYSTEM. THIS IS LIMITING POLEWARD
OUTFLOW BUT PROVIDING AN EASTWARD CHANNEL INTO THE TUTT CELL. LOW
VERTICAL WIND SHEAR AND WARM SST VALUES ARE FAVORABLE FOR
DEVELOPMENT.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A
NEAR-EQUATORIAL RIDGE POSITIONED TO THE SOUTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EASTWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: TD 15W HAS SLOWLY CONSOLIDATED WITHIN A
MARGINALLY-FAVORABLE ENVIRONMENT WHILE TRACKING SLOWLY EAST-
NORTHEASTWARD ALONG THE NORTHWEST PERIPHERY OF THE NEAR-EQUATORIAL
RIDGE. THIS TRACK MOTION WILL CONTINUE THROUGH TAU 36. AFTER TAU TAU
36, THE STEERING ENVIRONMENT WILL EVOLVE AS THE STRONG TUTT CELL TO
THE NORTHEAST TRACKS WESTWARD AND THE SUBTROPICAL RIDGE TO THE EAST
AND NORTHEAST RE-ALIGNS INTO A NORTH-SOUTH CONFIGURATION, WHICH WILL
STEER TD 15W NORTHWARD THROUGH TAU 72. ENVIRONMENTAL CONDITIONS SHOULD
GRADUALLY IMPROVE AS THE TUTT CELL SHIFTS TO THE NORTH, PROVIDING A
ROBUST POLEWARD OUTFLOW CHANNEL WHICH WILL AID IN INTENSIFICATION. THE
PEAK INTENSITY OF 75 KNOTS IS EXPECTED AROUND TAU 72 OVER WARM SST
(29-30C). AFTER TAU 72, SST WILL GRADUALLY COOL WITH EXTRA-TROPICAL
TRANSITION (ETT) EXPECTED TO COMMENCE BY TAU 96 AS THE SYSTEM BEGINS
TO INTERACT WITH THE MIDLATITUDE WESTERLIES AND BAROCLINIC ZONE. TD
15W WILL COMPLETE ETT BY TAU 120 AS IT GAINS FRONTAL CHARACTERISTICS
AND ACCELERATES NORTHEASTWARD WITHIN THE STRONG MIDLATITUDE
SOUTHWESTERLY FLOW.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
THROUGH TAU 72 WITH AN 85NM SPREAD IN SOLUTIONS AT TAU 72. THE
101200Z ECMWF ENSEMBLE (EPS) IS ALSO IN TIGHT AGREEMENT LENDING HIGH
CONFIDENCE TO THE JTWC FORECAST TRACK. AFTER TAU 72, THE
DETERMINISTIC GUIDANCE DIVERGES, MAINLY ALONG-TRACK, WITH A
SIGNIFICANT DIFFERENCE IN TRACK SPEEDS THUS MEDIUM CONFIDENCE.
RELIABLE INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH PEAK
INTENSITY VARYING FROM 60 KNOTS TO 88 KNOTS AT TAU 72. HWRF IS IN
THE MIDDLE OF THE PACK WITH A PEAK INTENSITY OF 73 KNOTS AT TAU 72.
OVERALL CONFIDENCE IN THE INTENSITY FORECAST IS MEDIUM DUE TO THE
EVOLVING UPPER-LEVEL PATTERN AND INTERACTION WITH THE TUTT
(CURRENTLY) AND THE TUTT CELL. THE COAMPS-TC ENSEMBLE INDICATES A
20 TO 30 PERCENT PROBABILITY OF RAPID INTENSIFICATION IN THE 36 TO
72 HOUR TIMEFRAME, WHICH COULD OCCUR IF THE SYSTEM DEVELOPS SLOWER
THAN EXPECTED OVER THE NEXT 36 HOURS THEN MORE RAPIDLY AS THE TUTT
CELL BOOSTS POLEWARD OUTFLOW.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN
NNNN