WDPN32 PGTW 110900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 155.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 352 NM SOUTH-SOUTHEAST OF MINAMI TORI
SHIMA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS NO SIGNIFICANT
CHANGE IN THE CONVECTIVE STRUCTURE AND DEGREE OF WRAP IN THE LAST
SIX HOURS. THE LOW LEVEL CIRCULATION REMAINS PARTIALLY EXPOSED
WHERE THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
HIGHER END OF AGENCY AND AUTOMATED DVORAK ESTIMATES (SEE BELOW) AND
REFLECTS THE SUSTAINED STRUCTURE OF THE SYSTEM. ENVIRONMENTAL
ANALYSIS INDICATES MARGINALLY FAVORABLE CONDITIONS FOR DEVELOPMENT
WITH STRONG POLEWARD OUTFLOW, MODERATE TO HIGH VWS, AND WARM SSTS.
TS 23W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF AN EASTERN
EXTENSION OF THE MID-LAYER OF THE STR TO THE NORTHWEST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: EXTENSION OF THE SUBTROPICAL RIDGE
(STR) TO THE NORTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 43 KTS AT 110540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: EXTRA-TROPICAL TRANSITION IS NOW
EXPECTED BEYOND THE FORECAST PERIOD, OTHERWISE, THERE ARE NO
SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS NAMTHEUN WILL CONTINUE ON ITS CURRENT TRACK
UP TO TAU 48. AFTERWARDS, A SECONDARY STR TO THE EAST-SOUTHEAST WILL
ASSUME STEERING AND DRIVE THE SYSTEM POLEWARD, MAKING IT CREST THE
STR AXIS NEAR TAU 72, THEN RECURVE AND ACCELERATE IT NORTHEASTWARD.
THE MARGINALLY FAVORABLE CONDITIONS WILL PROMOTE A STEADY
INTENSIFICATION TO A PEAK OF 65KTS BY TAU 72 AT THE STR CREST WHERE
VWS WILL BE AT MINIMUM. AFTERWARD, INCREASING VWS AND COOLING SSTS
WILL GRADUALLY DECAY THE SYSTEM DOWN TO 35KTS BY TAU 120. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH THE
WIDEST SPREAD OF 500+ NM AT TAU 72, ONLY BECAUSE OF UEMN AND AFUM,
THE EXTREME LEFT AND RIGHT OUTLIERS, RESPECTIVELY. IN VIEW OF THIS, 
THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK, LAID IN THE 
MIDDLE OF THE MODEL CLUSTER, UP TO TAU 72, AND MEDIUM CONFIDENCE 
AFTERWARD. COROLLARY TO THIS, THERE IS MEDIUM CONFIDENCE IN THE 
INTENSITY FORECAST UP TO TAU 72 AND LOW AFTERWARD.


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