WDXS31 PGTW 122100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07S (BAKUNG) WARNING NR
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.6S 95.3E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 236 NM NORTH-NORTHWEST OF THE COCOS
ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 07S (BAKUNG) WITH A HIGHLY COMPACT CORE OF DEEP CONVECTION.
WATER VAPOR IMAGERY REVEALS THE SYSTEM HAS A GOOD EQUATORWARD
OUTFLOW CHANNEL, IDENTIFIABLE BY CIRRUS FILAMENTS EXPANDING OUTWARD
IN THAT DIRECTION. FURTHER ENVIRONMENTAL ANALYSIS INDICATES THAT
07S IS IN A FAVORABLE ENVIRONMENT DUE TO LOW (5-10 KTS) VERTICAL
WIND SHEAR AND WARM (28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED
MSI. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK AND CIMSS OBJECTIVE INTENSITY
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK

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

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.0 - 45 KTS
   CIMSS SATCON: 41 KTS AT 121800Z
   CIMSS ADT: 41 KTS AT 121800Z
   CIMSS AIDT: 34 KTS AT 121800Z
   CIMSS D-MINT: 50 KTS AT 121843Z
   CIMSS D-PRINT: 37 KTS AT 121800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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: TROPICAL CYCLONE 07S (BAKUNG) IS FORECAST TO
TRACK WEST-SOUTHWESTWARD, ALONG THE NORTHERN PERIPHERY OF THE
SUBTROPICAL RIDGE TO THE SOUTH, THROUGH TAU 36. NEAR TAU 36, A
MAJOR SHORTWAVE TROUGH IS EXPECTED TO BREAK DOWN THE RIDGE, CAUSING
THE STEERING INFLUENCE TO SIGNIFICANTLY WEAKEN. THE SYSTEM WILL
LIKELY TRACK VERY SLOWLY AND ERRATICALLY FROM TAU 36 ALL THE WAY
THROUGH THE END OF THE FORECAST PERIOD. A WEAK STEERING INFLUENCE
FROM AN ELONGATED NEAR EQUATORIAL RIDGE (NER) THAT BUILDS NEAR
SOUTHERN SUMATRA AROUND TAU 60-72 IS FORECAST TO ASSIST IN A SLOW
EASTWARD MOVEMENT THROUGH THE REMAINDER OF THE FORECAST PERIOD.
REGARDING INTENSITY, 07S IS FORECAST TO STEADILY INTENSIFY THROUGH
TAU 36 AS THE ENVIRONMENT REMAINS FAVORABLE. AFTER TAU 36,
NORTHERLY VERTICAL WIND SHEAR IS EXPECTED TO INCREASE.
ADDITIONALLY, SLOW TRACK SPEEDS WILL CAUSE THE UPWELLING OF COOLER
WATER TO IMPACT THE SYSTEM. THESE TWO FACTORS ARE FORECAST TO
GRADUALLY WEAKEN 07S THROUGH THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT ONLY THROUGH TAU 36 WITH A 45 NM CROSS-TRACK SPREAD AT
THAT TIME. HOWEVER, AFTER TAU 36, MODELS DRASTICALLY BEGIN TO
DIFFER. THE WEAK STEERING PATTERN CAUSES MODELS TO SPLIT IN EVERY
DIRECTION. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS TROUGH TAU 36 AND THEN HEDGED CLOSER TO THE
GOOGLE DEEPMIND ENSEMBLE MEAN THROUGH TAU 120 WITH LOW CONFIDENCE.
INTENSITY GUIDANCE GENERALLY AGREES ON INTENSIFICATION THROUGH TAU
36-48 AND THEN GRADUAL WEAKENING THEREAFTER. HAFS-A CONTINUES TO BE
THE MOST AGGRESSIVE MODEL WITH A PEAK OF AROUND 80 KTS AT TAU 36.
THE JTWC INTENSITY FORECAST IS PLACED JUST BELOW THE CONSENSUS WITH
OVERALL MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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