WDPN32 PGTW 152100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING 
NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.9N 163.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 538 NM EAST-NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES TS
NAMTHEUN REMAINS FAIRLY WELL DEFINED AS IT MOVES INTO THE
MID-LATITUDES, WITH TIGHTLY CURVED BANDING WRAPPING INTO AN
OBSCURED LOW LEVEL CIRCULATION CENTER. DEEP CONVECTION IS SLIGHTLY
ASYMMETRIC, DUE TO THE PRESENCE OF MID TO UPPER LEVEL WESTERLY
SHEAR. A 151841Z GMI 37 GHZ COLOR COMPOSITE REVEALS THE LOW LEVEL
STRUCTURE, LENDING HIGH CONFIDENCE TO THE INITIAL POSITION, WHICH
WAS A BLEND OF MULTI-AGENCY FIXES. THE INITIAL INTENSITY IS
ASSESSED AT 50 KNOTS, BASED ON SUBJECTIVE DVORAK ESTIMATES OF
T3.0-3.5, WITH CIMSS ADT AND SATCON AT 51 KNOTS AND 52 KNOTS,
RESPECTIVELY AT ANALYSIS TIME. SUPPORTIVE SST AND ROBUST POLEWARD
OUTFLOW INTO A 60-PLUS KNOT JET TO THE NORTHEAST IS HELPING TO
OFFSET THE AFFECTS OF THE WESTERLY SHEAR.

INITIAL WIND RADII BASIS: PRIOR SCATTEROMETER DATA AND OBJECTIVE
BEST TRACK 

CURRENT STEERING MECHANISM: A BUILDING SUB-TROPICAL RIDGE TO THE
EAST IS TAKING OVER AS THE PRIMARY STEERING MECHANISM

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 49 KTS AT 151425Z
   CIMSS ADT: 53 KTS AT 151430Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: ---
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 EXPECTED TO SHIFT TO A MORE NORTHERLY
TRACK OVER THE NEXT 12 TO 24 HOURS AS THE STEERING RIDGE TO THE
EAST CONTINUES TO STRENGTHEN. HIGH AMPLITUDE FLOW IS ALLOWING
NAMTHEUN TO REMAIN TROPICAL AS IT TRACKS WELL INTO THE MID-
LATITUDES, AND IT HAS SO FAR REMAINED RESILIENT TO THE EFFECTS OF 
SHEAR. SST WILL REMAIN GENERALLY SUPPORTIVE FOR THE NEXT 12-24 
HOURS. EXTRA-TROPICAL TRANSITION (ETT) WILL BEGIN AROUND TAU 36, AND 
BE WELL UNDERWAY BY TAU 48 AS THE SYSTEM BEGINS TO ROUND THE RIDGE. 
AT THE SAME TIME, IT WILL INCREASINGLY FEEL THE INFLUENCE OF AN 
APPROACHING TROUGH. TS 23W WILL COMPLETE ETT BY TAU 72, WITH THE 
REMNANT GALE-FORCE LOW ACCELERATING TO THE NORTHEAST.


MODEL DISCUSSION: NUMERICAL MODELS REMAIN IN VERY TIGHT AGREEMENT,
LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST THAT IS LAID
CLOSE TO THE MULTI-MODEL CONSENSUS. CONFIDENCE IN THE INTENSITY
FORECAST IS SET AT MEDIUM DUE TO UNCERTAINTIES ASSOCIATED WITH ETT.  


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