Tropical Storm MERBOK Advisory So, 11.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN)
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 21.2N 159.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 354 NM EAST-SOUTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS LOW-LEVEL
CLOUD LINES WRAPPING INTO A PARTIALLY-EXPOSED, BROAD LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH FRAGMENTED CONVECTIVE BANDING. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE MSI.
THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
AND IS HEDGED ABOVE THE PGTW DVORAK ESTIMATE. A 102254Z AMSU-B 89GHZ
MICROWAVE IMAGE INDICATES FORMATIVE BANDING OVER THE SOUTHERN
SEMICIRCLE AND EASTERN QUADRANT WITH SHALLOW, WEAK BANDING OVER THE
NORTHERN SEMICIRCLE. UPPER-LEVEL CONDITIONS ARE COMPLEX AND
MARGINALLY-FAVORABLE WITH THE TUTT EXTENDING FROM A TUTT CELL NEAR
30N 168E 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
   KNES: T1.0 - 25 KTS
   CIMSS ADT: 33 KTS AT 102340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EASTWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   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 15W HAS MAINTAINED A BROAD LOW-LEVEL
CIRCULATION CENTER WITH FORMATIVE BANDING 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 24. AFTER TAU 24, 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 (28C).
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 A 75NM SPREAD IN SOLUTIONS AT TAU 72. THE
101800Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) ARE 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 70 KNOTS TO 84 KNOTS AT TAU 72. HWRF IS
IN THE MIDDLE OF THE PACK WITH A PEAK INTENSITY OF 75 KNOTS AT TAU
84. 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 101800Z COAMPS-TC ENSEMBLE
INDICATES A 40 TO 60 PERCENT PROBABILITY OF RAPID INTENSIFICATION IN
THE 24 TO 72 HOUR TIMEFRAME.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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