WDPN32 PGTW 141500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING 
NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.5N 158.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 219 NM EAST OF MINAMI TORI SHIMA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
MEDIUM-SIZED SYSTEM WITH PERSISTENT DEEP CONVECTION OVER THE
CENTRAL DENSE OVERCAST. THE INITIAL POSITION IS EXTRAPOLATED
WITH MEDIUM CONFIDENCE BASED ON A SEMI-CIRCULATION FEATURE FROM A
141120Z PARTIAL ASCAT PASS. THE INITIAL INTENSITY OF 35KTS IS
PLACED WITH MEDIUM CONFIDENCE BASED ON AN OVERALL ASSESSMENT OF
AGENCY AND AUTOMATED DVORAK ESTIMATES. ANALYSIS INDICATES A
MARGINALLY FAVORABLE ENVIRONMENT WITH STRONG EQUATORWARD OUTFLOW
AND WARM SST OFFSET BY STRONG VWS. THE SYSTEM IS EXHIBITING
SUBTROPICAL CHARACTERISTICS, I.E., ASYMMETRIC WIND FIELD AND
VORTICITY SIGNATURES. THERE IS ALSO SUBSIDENCE ALONG THE NORTHERN
PERIPHERY DUE TO THE PROXIMITY OF AN UPPER LEVEL LOW TO THE
NORTHEAST. THE CYCLONE IS TRACKING ON THE POLEWARD SIDE OF THE STR
TO THE SOUTH.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD

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

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 WILL ASSUME
STEERING AND DRIVE THE SYSTEM NORTHWARD THEN ACCELERATE IT
NORTHEASTWARD AFTER TAU 72. THE MARGINALLY FAVORABLE ENVIRONMENT
WILL FUEL A SLIGHT INTENSIFICATION TO 40KTS AND SUSTAIN IT UP TO
TAU 48. AFTERWARD, INCREASING VWS AND COOLING SSTS WILL GRADUALLY
ERODE THE SYSTEM DOWN TO 30KTS BY TAU 96. CONCURRENTLY, THE CYCLONE
WILL CONTINUE TO GAIN MORE SUBTROPICAL CHARACTERISTICS, THEN AROUND
TAU 72, WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT APPROACHES
THE BAROCLINIC ZONE. BY TAU 120, TS 23W WILL BECOME A MODERATE
GALE-FORCE COLD CORE LOW. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT,
GRADUALLY SPREADING TO 210M AT TAU 72 AT ITS WIDEST, LENDING MEDIUM
CONFIDENCE TO UP TO TAU 72 THEN LOW CONFIDENCE AFTERWARD DUE TO
UNCERTAINTIES IN THE STORM SPEED DURING ETT. THERE IS ALSO MEDIUM
CONFIDENCE THE INTENSITY FORECAST UP TO TAU 72 AND LOW CONFIDENCE
AFTERWARD. 

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