WDPN32 PGTW 111500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.2N 154.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 302 NM SOUTH OF MINAMI TORI SHIMA, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL (MSI) AND ENHANCED INFRARED (EIR) SATELLITE
IMAGERY SHOWS INCREASED AND DEEPENED CENTRAL CONVECTION. THE LOW
LEVEL CIRCULATION HAS BECOME OBSCURED BY THE INCREASED CONVECTION.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE USING LOW
CLOUD TRACING IN THE MSI AND EXTRAPOLATED INTO THE CENTRAL
CONVECTION IN THE EIR. THE INITIAL INTENSITY OF 50KTS IS ASSESSED
WITH MEDIUM CONFIDENCE AND HELD SLIGHTLY HIGHER THAN AGENCY AND
AUTOMATED DVORAK ESTIMATES TO REFLECT THE IMPROVED CONVECTIVE 
STRUCTURE OF THE SYSTEM. ENVIRONMENTAL ANALYSIS NOW INDICATES 
MARGINALLY UNFAVORABLE CONDITIONS FOR DEVELOPMENT WITH STRONG 
POLEWARD OUTFLOW AND WARM SSTS OFFSET BY HIGH VWS. 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: RECENT 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: 39 KTS AT 111140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 25-30 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 NAMTHEUN WILL CONTINUE ON ITS CURRENT TRACK
UP TO TAU 48. AFTERWARD, A SECONDARY STR TO THE EAST-SOUTHEAST WILL
ASSUME STEERING AND DRIVE THE SYSTEM POLEWARD, MAKING IT CREST THE
STR AXIS JUST AFTER TAU 48,  THEN RECURVE AND DRIVE IT 
NORTHEASTWARD. THE MARGINALLY UNFAVORABLE CONDITIONS WILL SLIGHTLY 
WEAKEN THE SYSTEM DOWN TO 45KTS BY TAU 36. AFTERWARD, DECREASING VWS 
NEAR THE CREST WILL RE-INTENSIFY THE SYSTEM TO 55KTS BY TAU 48. 
AFTERWARD, VWS WILL ONCE AGAIN INCREASE AND SSTS WILL START TO COOL 
AS THE CYCLONE GAINS LATITUDE. THESE COMBINED EFFECTS WILL GRADUALLY 
DECAY THE SYSTEM DOWN TO 35KTS BY TAU 120. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH THE
WIDEST SPREAD OF 410+ NM AT TAU 72, ONLY BECAUSE OF UEMN AND GFS,
THE EXTREME LEFT AND RIGHT OUTLIERS, RESPECTIVELY. IN VIEW OF THIS,
THERE IS MEDIUM CONFIDENCE IN THE JTWC FORECAST TRACK, LAID IN THE
MIDDLE OF THE MODEL CLUSTER, UP TO TAU 72, AND LOW CONFIDENCE
AFTERWARD. COROLLARY TO THIS, THERE IS ALSO 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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