WDXS32 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.5S 94.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 283 NM SOUTH-SOUTHWEST OF THE COCOS
ISLANDS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 13S (VINCE) WITH SPIRAL BANDS OF DEEP CONVECTION WRAPPING
INTO THE OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC). EASTERLY
SHEAR IS EVIDENT BY THE CONVECTION DRIFTING OFF TO THE WEST, AWAY
FROM THE SYSTEM. ENVIRONMENTAL ANALYSIS INDICATES THAT 13S IS IN A
MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE
POLEWARD OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS) EASTERLY
VERTICAL WIND SHEAR, AND WARM (27-28 C) SEA SURFACE TEMPERATURES.
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
TIGHTLY WOUND LOW-LEVEL CLOUD LINES IN THE ANIMATED MSI. THE
INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE FROM EARLIER SMOS DATA.

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   APRF: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 030600Z
   CIMSS AIDT: 43 KTS AT 030600Z
   CIMSS DPRINT: 58 KTS AT 030700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: 13S IS FORECAST TO CONTINUE TRACKING
WEST-SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE STR
THROUGH TAU 72. AROUND TAU 72, A SECONDARY RIDGE WILL BUILD SOUTH
OF THE SYSTEM, DRIVING IT FURTHER WEST-SOUTHWESTWARD. IT WILL
CONTINUE ON THIS TRAJECTORY THROUGH THE REMAINDER OF THE FORECAST
PERIOD. REGARDING INTENSITY, 13S IS FORECAST TO MARGINALLY
INTENSIFY TO 70 KTS AT TAU 72 DUE TO THE PERSISTENT VERTICAL WIND
SHEAR HINDERING DEVELOPMENT AND LACK OF A GOOD OUTFLOW CHANNEL.
AROUND TAU 72, POLEWARD OUTFLOW IS ANTICIPATED TO INCREASE AND
VERTICAL WIND SHEAR DECREASE, ALLOWING FOR FURTHER INTENSIFICATION.
THE MAIN FACTOR CONCERNING INTENSITY AFTER TAU 72 WILL BE THE
TRAJECTORY OF THE TRACK. IF IT IS MORE WESTWARD VICE SOUTHWESTWARD,
THE VORTEX WILL INTERACT WITH WARMER WATERS.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
WITH A 105 NM CROSS-TRACK SPREAD AT TAU 72. AFTER TAU 72, MODELS
BEGIN TO DIVERGE DUE TO THE DIFFERENCES IN HOW THE VORTEX BEGINS TO
INTERACT WITH THE NEWLY FORMED RIDGE TO THE SOUTH. ECMWF TRACKS THE
SYSTEM MORE SOUTHWESTWARD, ALONG THE NORTHWESTERN PERIPHERY OF THE
RIDGE, WHILE GFS TRACKS NEARLY STRAIGHT WESTWARD. THE JTWC TRACK
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER.
INTENSITY GUIDANCE IS IN WORSE AGREEMENT WITH FRIA (AN RI AID)
TRIGGERING. COAMPS-TC IS A MAJOR OUTLIER, DEPICTING STEADY
WEAKENING THROUGHOUT THE FORECAST PERIOD. THE REMAINDER OF GUIDANCE
SUGGESTS GRADUAL DEVELOPMENT THROUGH TAU 48. AFTER TAU 48, THE
MENTIONED TRACK DIFFERENCES CAUSE THERE TO BE DECREASED CONFIDENCE
IN INTENSITY. HAFS-A AND HWRF BOTH SUGGEST FURTHER INTENSIFICATION
DUE TO THEIR WESTWARD TRACK VICE SOUTHWESTWARD. THE JTWC INTENSITY
FORECAST FOLLOWS CLOSE TO CONSENSUS THROUGH TAU 48, AND THEN
SLIGHTLY HIGHER AFTERWARDS. 

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