WDXS31 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07S (SEVEN) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.4S 97.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 229 NM NORTH OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 07S HAS IMPROVED SIGNIFICANTLY OVER THE PAST
12 HOURS, WITH OVERALL BETTER ORGANIZATION, IMPROVED DEEP
CONVECTIVE BANDING, AND ENHANCED NEAR-RADIAL UPPER-LEVEL OUTFLOW.
THE ENVIRONMENT REMAINS FAVORABLE FOR DEVELOPMENT, CHARACTERIZED BY
WARM (28-29 C) SEA SURFACE TEMPERATURES, VERY LOW (0-5 KTS)
VERTICAL WIND SHEAR (VWS), AND HIGH MOISTURE CONTENT. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON PARTIALLY
EXPOSED LOW-LEVEL CLOUD BANDING WRAPPING INTO THE CORE CONVECTION.
THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE PGTW 2.5 DVORAK INTENSITY.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 07S IS EXPECTED TO TRACK WEST-SOUTHWESTWARD
THROUGH TAU 36. BEGINNING AROUND TAU 36, A MAJOR SHORTWAVE TROUGH
WILL BEGIN TO WEAKEN THE STEERING RIDGE TO THE SOUTH OF THE SYSTEM,
LEADING TO A WEAK AND COMPETING STEERING ENVIRONMENT. AS A RESULT,
07S WILL DRIFT SLOWLY WEST-SOUTHWESTWARD AND STALL BETWEEN TAU
48-96, UNTIL THE NEAR EQUATORIAL RIDGE (NER) BECOMES THE DOMINANT
STEERING INFLUENCE. NEAR THE END OF THE FORECAST PERIOD, THE NER
WILL CAUSE 07S TO DRIFT EASTWARD THROUGH TAU 120. REGARDING
INTENSITY, 07S WILL STEADILY INTENSIFY WHILE WITHIN THE FAVORABLE
ENVIRONMENT, AND IS EXPECTED TO PEAK AT 55 KTS AROUND TAU 48.
BEGINNING AROUND TAU 48-60, THE VWS WILL INCREASE SIGNIFICANTLY,
CONTRIBUTING TO THE WEAKENING TREND THROUGH THE END OF THE FORECAST
PERIOD. THE QUASI-STATIONARY PERIOD BETWEEN TAU 48-96 COULD LEAD
TO COOL WATER UPWELLING, WHICH WOULD ALSO WEAKEN THE SYSTEM. THE
WEAKENING TREND WILL CONTRIBUTE TO THE NER TAKING OVER AS THE PRIMARY
STEERING INFLUENCE, AS THE SHALLOWER VORTEX WILL BE MORE SUSCEPTIBLE
TO LOWER-LEVEL FLOW.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN FAIR
AGREEMENT THROUGH TAU 36, WITH MODELS AGREEING ON A WEST-SOUTHWESTWARD 
TRACK. AFTER TAU 36, HOWEVER, MODEL GUIDANCE DIVERGES SIGNIFICANTLY 
DUE TO THE DETERIORATING STEERING ENVIRONMENT. MODELS DISAGREE ON THE 
TIMING OF THE EASTWARD CURL AND THE TRACK SPEEDS LEADING UP TO AND 
FOLLOWING THE TURN. CONFIDENCE AFTER TAU 72 IS LOW DUE TO THE 
UNCERTAINTY REGARDING THE WEAK STEERING PATTERN IN THE LATER TAUS, THE 
TRACK SPEEDS AFTER 07S COMES UNDER THE INFLUENCE OF THE NER, AND THE 
ORIENTATION OF THE EASTWARD TURN. INTENSITY AIDS ARE IN GOOD AGREEMENT 
THROUGH THE FORECAST PERIOD, WITH ALL MODELS DEPICTING A STEADY 
INTENSIFICATION THROUGH TAU 48-72, FOLLOWED BY A STEADY WEAKENING 
THROUGH TAU 120. AS A RESULT, THE JTWC INTENSITY FORECAST IS PLACED 
WITH OVERALL MEDIUM CONFIDENCE.

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