Tropical Storm NAMTHEUN Advisory vie, 15-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NAMTHEUN) WARNING
NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 25.6N 160.0E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 337 NM EAST-NORTHEAST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
MEDIUM-SIZED SYSTEM WITH PERSISTENT DEEP CONVECTION CENTERING NEAR
THE MAIN LOW-LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS
EXTRAPOLATED WITH LOW CONFIDENCE BASED ON A 142040Z SSMIS 91GHZ
MICROWAVE IMAGE. THE INITIAL INTENSITY OF 40KTS IS PLACED WITH
MEDIUM CONFIDENCE BASED ON AN OVERALL ASSESSMENT OF MULTIPLE
AGENCIES, AUTOMATED DVORAK ESTIMATES (ADT), AND SATELLITE CONSENSUS
(SATCON). ANALYSIS INDICATES A MARGINALLY FAVORABLE ENVIRONMENT
WITH MODERATE POLEWARD AND EQUATORWARD OUTFLOW AND WARM SST OFFSET
BY STRONG WESTERLY VWS. THE CYCLONE IS CONTINUING A TRACK ON THE
POLEWARD SIDE OF THE STR TO THE SOUTH.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE SOUTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 53 KTS AT 142309Z
   CIMSS ADT: 51 KTS AT 150110Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW
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 24. AFTERWARD, A SECONDARY STR TO THE EAST WILL ASSUME
STEERING AND DRIVE THE SYSTEM NORTHWARD, THEN ACCELERATE IT
NORTHEASTWARD AFTER TAU 48. THE MARGINALLY FAVORABLE ENVIRONMENT
WILL HOLD THE INTENSITY AT 40KTS FOR THE NEXT 12 HOURS. AFTERWARD,
INCREASING VWS AND COOLING SSTS WILL BEGIN ERODING THE SYSTEM DOWN
TO 30KTS BY TAU 48. CONCURRENTLY, THE CYCLONE WILL BEGIN TO UNDERGO
EXTRA-TROPICAL TRANSITION (ETT) AS IT APPROACHES THE BAROCLINIC
ZONE. BETWEEN TAU 48 AND 72, TS 23W WILL BECOME A MODERATE
GALE-FORCE COLD-CORE LOW, COMPLETING ETT BY TAU 72.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY TIGHT AGREEMENT,
NAVGEM WAS UNAVAILABLE FOR THE MULTIPLE MODEL CONSENSUS. HOWEVER,
WITH THE REMAINING MODELS, THERE IS ONLY A GRADUAL SPREAD AT THE
WIDEST TO 100NM BY TAU 72, LENDING MEDIUM CONFIDENCE THROUGH TAU
72. THE ALONG TRACK UNCERTAINTY BETWEEN 48 AND 72 LENDS LOW
CONFIDENCE DURING THIS 24 HOUR TIMEFRAME AS THE SYSTEM TRANSITIONS
TO ETT. THERE IS ALSO MEDIUM CONFIDENCE IN THE INTENSITY FORECAST
UP TO TAU 48, AND LOW THEREAFTER.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
NNNN
NNNN