WDPS31 PGTW 150900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 30P (THIRTY) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.7S 171.1E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTHEAST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 22 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE AND
RELATIVELY SYMMETRICAL CENTRAL DENSE OVERCAST (CDO) LIKE FEATURE.
HOWEVER, WHILE TEMPTING LOCATE THE LOW LEVEL CIRCULATION CENTER
(LLCC) DIRECTLY UNDER THE OVERSHOOTING CLOUD TOPS, THE VORTEX IS
SIGNIFICANTLY TILTED AND LOCATED FAR AWAY FROM THE DEEPEST OF THE
CONVECTION. A 150431Z F18 SSMIS 91GHZ COLOR ENHANCED MICROWAVE
IMAGE REVEALS THE LLCC IS ACTUALLY LOCATED APPROXIMATELY 55NM
NORTHWEST OF THE OVERSHOOTING TOPS ASSOCIATED WITH THE CDO-LIKE
FEATURE. HOWEVER, CIRRUS DEBRIS IS KEEPING THE LLCC HIDDEN FROM
VIEW IN GEOSTATIONARY IMAGERY. THE INITIAL POSITION IS ASSESSED
WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE 0431Z
POSITION IN THE MICROWAVE IMAGERY NOTED ABOVE. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN AVERAGE OF
THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES OUTLINED ABOVE.
THE ENVIRONMENT IS BECOMING INCREASINGLY HOSTILE, WITH INCREASING
SHEAR (THOUGH CURRENTLY STILL LOW TO MODERATE), AND COOLING SSTS,
OFFSET BY EXTREMELY STRONG DIVERGENT POLEWARD OUTFLOW ON THE EAST
SIDE OF A DEEP UPPER-LEVEL TROUGH TO THE WEST.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A LARGE DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR TONGA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 43 KTS AT 150340Z
   CIMSS ADT: 55 KTS AT 150540Z
   CIMSS AIDT: 45 KTS AT 150540Z
   CIMSS D-MINT: 35 KTS AT 150430Z
   CIMSS D-PRINT: 40 KTS AT 150540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: HIGH LEVEL OF VORTEX MISALIGNMENT. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TROPICAL CYCLONE (TC) 29S (TWENTY-NINE) IS
FORECAST TO CONTINUE TRACKING SOUTH-SOUTHEASTWARD ALONG THE WEST
SIDE OF THE STRONG STR TO THE EAST OVER THE NEXT 12 HOURS. TRACK
SPEEDS WILL CONTINUE TO INCREASE AS THE STEERING GRADIENT TIGHTENS
BETWEEN THE STR AND A STRONG, DEEP AREA OF LOW PRESSURE IN THE
TASMAN SEA. TC 29S WILL TURN SOUTH, THEN SOUTHWEST AFTER TAU 12, AS
THE DEEPENING LOW IN THE TASMAN SEA BEGINS TO PULL TC 29S IN
TOWARDS ITSELF AND THE TWO SYSTEMS BEGIN TO UNDERGO BINARY
INTERACTION. BY THE END OF THE FORECAST, TC 29S WILL BE DIVING IN
TOWARDS THE DEVELOPING LOW AT 25 KNOTS OR MORE DUE TO THE EXTREMELY
STRONG GRADIENT BETWEEN THE LOW AND THE STR. IN TERMS OF INTENSITY,
TC 29S WILL CONTINUE TO INTENSIFY OVER THE NEXT 12 HOURS, PRIMARILY
DUE TO THE STRONG GRADIENT FLOW WHICH EXTENDS THROUGH THE DEPTH OF
THE ATMOSPHERE AND INCREASING BAROCLINIC FORCING AS THE SYSTEM
BEGINS TO INTERACT WITH THE SUBTROPICAL JET. MAXIMUM INTENSITY IS
EXPECTED TO OCCUR BETWEEN TAU 12 AND TAU 24, BEFORE THE SYSTEM
STARTS TO SLOW WEAKEN BEYOND THE END OF THE FORECAST PERIOD. TC 29S
HAS ALREADY BEGUN THE SUBTROPICAL TRANSITION (STT) PROCESS, WITH
THE VORTEX BECOMING DECOUPLED AND SHALLOWING OUT AT A RAPID PACE.
THE SYSTEM SHOULD CROSS THE 26C ISOTHERM WITHIN THE NEXT 12 HOURS
AND START TO TRULY INTERACT WITH THE SUBTROPICAL JET STREAM AT THE
SAME TIME. TC 29S WILL MOVE DIRECTLY UNDER THE NOSE OF A 100 KNOT
JET MAX AROUND TAU 24, MARKING STT COMPLETION.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH THE SHORT DURATION OF THE FORECAST PERIOD,
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH THE BULK OF THE GUIDANCE
DEPICTING INTENSIFICATION THROUGH TAU 24, WITH A MARGINAL SPREAD IN
PEAK INTENSITIES BETWEEN 55 AND 60 KNOTS. THE JTWC FORECAST IS SET
CLOSE TO THE HAFS-A AND COAMPS-TC SOLUTIONS, WITH MEDIUM
CONFIDENCE. 

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