WDPN32 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.8N 151.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 291 NM SOUTH-SOUTHWEST OF MINAMI TORI
SHIMA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW-LEVEL CIRCULATION WITH PERSISTENT DEEP
CONVECTION SHEARED OVER THE NORTHERN SEMICIRCLE. A 120955Z GMI
89GHZ COLOR COMPOSITE MICROWAVE IMAGE INDICATES TIGHTLY-WRAPPED
SHALLOW BANDING WRAPPING INTO A RAGGED BUT DEFINED CENTER, HOWEVER,
THE DEEP CONVECTIVE STRUCTURE IS FRAGMENTED AND LIMITED TO THE
NORTHEAST QUADRANT. THE ENVIRONMENT REMAINS MARGINAL WITH MODERATE
SOUTHERLY VERTICAL WIND SHEAR OFFSET SLIGHTLY BY STRONG SOUTHERLY
UPPER-LEVEL FLOW. THE INITIAL POSITION IS PLACED WITH MODERATE
CONFIDENCE BASED ON EIR. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH MODERATE CONFIDENCE BASED ON AGENCY DVORAK ESTIMATES
AND THE 121140Z ADT ESTIMATE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) EXTENDING WESTWARD FROM 40N AND 180 TO THE
VICINITY OF KYUSHU. A SECOND RIDGE BUILDING TO THE SOUTHEAST IS
MOVING WEST, PROVIDING A BOOST TO THE WEST-NORTHWEST MOVEMENT. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 35 KTS AT 121140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 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 23W IS TRACKING UNDER THE COMPETING
STEERING INFLUENCE OF A LOW-LEVEL STR TO THE NORTH AND A SECONDARY
STEERING RIDGE BUILDING TO THE SOUTHEAST. TS 23W SHOULD PEAK AT 40
KNOTS THEN STEADILY WEAKEN THROUGH THE FORECAST AS IT TRACKS UNDER
STRONG UPPER LEVEL SOUTHWESTERLIES AND OVER COOLER SST. EXTRA-
TROPICAL TRANSITION IS UNLIKELY DUE TO THE LACK OF A STRONG
BAROCLINIC ZONE SO THE SYSTEM WILL LIKELY DISSIPATE BY TAU 96 OR
EARLIER.  

MODEL DISCUSSION: DUE TO A FAIRLY COMPLEX, EVOLVING STEERING
PATTERN, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH HIGH
UNCERTAINTY IN THE RECURVE TIMING AND LOCATION. THE JTWC FORECAST
IS POSITIONED LEFT OF THE MULTI-MODEL CONSENSUS (CONW) THROUGH TAU
36. AFTER TAU 36, THE JTWC FORECAST IS POSITIONED CLOSE TO CONW. 

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