WDXS31 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07S (BAKUNG) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.6S 93.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 220 NM WEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 00 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
DEFIANT VORTEX THAT HAS THUS FAR RESISTED DECOUPLING IN THE FACE OF
A COMPLEX VERTICAL SHEAR PROFILE, WITH SOUTH-EASTERLIES NEAR THE
SURFACE, WESTERLIES IN THE MID-TROPOSPHERE, AND NORTH-EASTERLIES IN
THE UPPER TROPOSPHERE. THE MAXIMUM SHEAR MAGNITUDE WITHIN THIS
PROFILE IS 20-25 KT. DESPITE THIS, VORTEX TILT REMAINS MILD, WITH
THE LOW-LEVEL CIRCULATION CENTER (LLCC) TUCKED JUST BENEATH THE 
NORTHEASTERN PERIPHERY OF THE CENTRAL DENSE OVERCAST, WHICH HAS 
PERSISTED IN DEPTH AND COVERAGE OVER THE PAST TWELVE HOURS. IN RECENT 
HOURS, UPPER-LEVEL CIRRUS OUTFLOW HAS IMPROVED IN ALL QUADRANTS IN 
RESPONSE TO A LOCAL MAXIMUM IN CONVECTIVE ACTIVITY. A PARTIAL 161454Z 
ASCAT-C SCATTEROMETER PASS SHOWED A STILL COMPACT CIRCULATION WITH 
GALES PREDOMINANTLY CONFINED TO THE SOUTHERN SEMICIRCLE. SUBJECTIVE 
AND OBJECTIVE SATELLITE-BASED INTENSITY ESTIMATES RANGE FROM BELOW 40
KT TO 55 KT. THE INITIAL INTENSITY IS MAINTAINED AT 45 KT FOR THIS
WARNING BASED ON A BLEND OF THESE DATA. THE INITIAL MOTION IS
QUASI-STATIONARY, AS THE COMPLEX SHEAR PROFILE DOUBLES AS A COMPLEX
STEERING PROFILE, WHICH IS IMPARTING A NET ZERO STEERING FORCE ON
THE CYCLONE FOR NOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE SOUTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   CIMSS AIDT: 36 KTS AT 161420Z
   CIMSS D-PRINT: 48 KTS AT 161720Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR MASS TO THE WEST, NORTH, AND
NORTHEAST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TROPICAL CYCLONE 07S (BAKUNG) HAS MAINTAINED
STEADY INTENSITY FOR LONGER THAN FORECAST IN A COMPLEX SHEAR
ENVIRONMENT, FORESTALLING THE CYCLONE'S TERMINAL DECAY. DYNAMICAL
MODEL GUIDANCE, HOWEVER, CONTINUES TO INSIST THAT VORTEX DECOUPLING
IS IMMINENT, WITH HAFS-A, HWRF, GFS, AND ECMWF ALL SHOWING
CATASTROPHIC DISINTEGRATION OF THE VORTEX BY 24 HOURS.
MID-TROPOSPHERIC WESTERLIES PUSHING INTO THE VORTEX WILL EVENTUALLY
VENTILATE THE INNER CORE WITH THE DRY AIR MASS POSITIONED WEST OF
THE CIRCULATION. THE MOST EVIDENT DIFFERENCE IN THE ENVIRONMENT
VERSUS 24 HOURS AGO IS THAT THIS DRY AIR MASS HAS NOW FULLY WRAPPED
AROUND THE NORTHERN SEMICIRCLE AND IS NOW PRESENT NORTH AND
NORTHEAST OF THE STORM CENTER AS WELL. THIS SHOULD INCREASE
VENTILATION RELATIVE TO YESTERDAY, AS UPPER TROPOSPHERIC
NORTH-EASTERLIES ADVECT ADDITIONAL DRY AIR INTO THE CIRCULATION.
EVENTUAL DISRUPTION OF THE DEEP CONVECTIVE CORE AND FORCIBLE
SEPARATION OF THE SURFACE CIRCULATION FROM THE CONVECTION IS THUS
LOGICAL. THE JTWC INTENSITY FORECAST SHOWS STEADY WEAKENING TO
BELOW WARNING THRESHOLD BY 36 HOURS, AT WHICH TIME THE FORECAST
TERMINATES. THE CYCLONE'S SHORT-TERM MOTION IS SOMEWHAT UNCERTAIN
DUE TO THE UNCERTAIN TIMING OF VORTEX DECOUPLING AND THE EVOLUTION
OF THE EFFECTIVE STEERING LAYER. DYNAMICAL MODELS HAVE SHIFTED
TOWARDS A NORTHWESTERLY MOTION DURING THE DECOUPLING PHASE, THOUGH
WITH ELEVATED SPREAD. THE ECMWF, AIFS, AND GOOGLE DEEPMIND ENSEMBLE
MEAN MAKE UP THE RIGHT-HAND SIDE OF THE TRACK ENVELOPE WITH A MORE
NORTHWARD TRACK, WHILE OTHER PHYSICAL MODELS TRACK 07S MORE
NORTHWESTWARD AND MAKE UP THE LEFT-HAND SIDE OF THE ENVELOPE. THE
JTWC FORECAST SPLITS THE DIFFERENCE THROUGH TERMINATION AT 36
HOURS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS SLIGHTLY EAST OF THE
MULTI-MODEL CONSENSUS. THE JTWC INTENSITY FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS, LARGELY IGNORING THE SHIPS STATISTICAL
INTENSITY AID, WHICH IS SIGNIFICANTLY HIGHER THAN THE DYNAMICAL
MODEL AIDS AND IS DEEMED UNREALISTIC.

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