WDXS31 PGTW 140900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 07S (BAKUNG) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.4S 91.2E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 352 NM WEST-NORTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) INDICATES A VERY
COMPACT TROPICAL CYCLONE, WITH A SMALL AREA OF DEEP CONVECTION AT
THE HEAD OF A COMMA-SHAPED FEATURE. ANALYSIS OF EARLIER ENHANCED
INFRARED (EIR) IMAGERY SHOWS THAT THE SYSTEM BRIEFLY DEVELOPED AN
EYE AROUND 140000Z, ONLY TO HAVE IT RAPIDLY FILL AND THE SATELLITE
DEPICTION HAS RAPIDLY DEGRADED EVER SINCE. THE EIR IMAGERY ALSO
SHOWS A VERY SHARP EASTERN EDGE OF THE CIRRUS SHIELD, CONSISTENT WITH
THE MODEL-BASED ANALYSIS OF RELATIVELY STRONG DEEP-LAYER
EAST-NORTHEASTERLY SHEAR. DUE TO A LACK OF RECENT MICROWAVE
IMAGERY, AND OBSCURATION OF THE LOW-LEVEL STRUCTURE, THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED SOLELY ON ANALYSIS OF
THE EIR FROM THE GOES-IO SATELLITE. SIMILARLY, DUE TO UPSTREAM
COMMUNICATIONS ISSUES, CIMSS OBJECTIVE SATELLITE INTENSITY
ESTIMATES ARE LARGELY UNAVAILABLE, AND THE INITIAL INTENSITY IS
ASSESSED WITH LOW CONFIDENCE USING JUST TWO AGENCY (PGTW AND APRF)
DVORAK CURRENT INTENSITY ESTIMATES. DUE TO THE VERY COMPACT NATURE
OF THE SYSTEM, THE DVORAK ESTIMATES ARE LIKELY NON-REPRESENTATIVE.
ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE, WITH MODERATE
EASTERLY SHEAR, MODERATE POLEWARD OUTFLOW AND WARM SSTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A NEAR-EQUATORIAL
RIDGE (NER) WHICH EXTENDS FROM SOUTHERN BORNEO TO NEAR 20S 90E. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   APRF: T5.5 - 102 KTS
   CIMSS D-PRINT: 46 KTS AT 140600Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: DUE TO THE RECENT TRANSFER OF SERVICE
OUTAGE, THIS IS THE FIRST JTWC WARNING FOR TC 07S SINCE WARNING
NUMBER THREE, AND THUS THERE ARE SIGNIFICANT CHANGES FROM THE LAST
WARNING, IN TERMS OF BOTH THE TRACK AND INTENSITY FORECAST. 

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 07S HAS TRACKED
SOUTHWESTWARD AT A STEADY CLIP OVER THE PAST COUPLE OF DAYS, ALONG
THE WESTERN SIDE OF THE NER WHICH LIES TO THE EAST OF THE SYSTEM.
HOWEVER, THE SYSTEM IS RAPIDLY SLOWING DOWN AS AN APPROACHING TROF
MOVES IN FROM THE WEST AND IS ERODING THE RIDGE, WEAKENING THE
STEERING GRADIENT. OVER THE NEXT 12 HOURS OR SO, TC 07S WILL DRIFT
SLOWLY TOWARDS THE SOUTHWEST UNDER THE INFLUENCE OF THE RAPIDLY
WEAKENING RIDGE TO THE EAST. THE SYSTEM REACHES AN INFLECTION POINT
BY TAU 12 AND WILL BE PUSHED EASTWARD BY THE COMBINED INFLUENCE OF
THE TROF PASSING FAR TO THE SOUTH AND A STRENGTHENING NER SITUATED
ALONG THE EQUATOR FROM SUMATRA ALL THE WAY TO THE MALDIVES. TC 07S
WILL TRACK EASTWARD ALONG THE SOUTHERN SIDE OF THE NER THROUGH TAU
48, BEFORE IT ONCE AGAIN REACHES AN INFLECTION POINT AS THE NER TO
THE NORTH BEGINS TO RECEDE WESTWARD, WHILE SIMULTANEOUSLY A
SUBTROPICAL RIDGE (STR) BUILDS NORTHWESTWARD FROM WESTERN AUSTRALIA
AND LITERALLY PUSHES TC 07S SLOWLY NORTHWARD. IN TERMS OF
INTENSITY, THE SYSTEM HAS ALREADY PEAKED IN INTENSITY BUT LOOKS TO
BE ABLE TO RESIST THE MODERATE EASTERLY SHEAR FOR A BIT LONGER AND
MAINTAIN ITS CURRENT INTENSITY. AFTER IT BEGINS TO TURN EASTWARD
HOWEVER, SHEAR WILL INCREASE FURTHER, AND BEGIN THE SLOW BUT STEADY
WEAKENING PROCESS, WHICH WILL CONTINUE THROUGH THE BULK OF THE
FORECAST PERIOD. DRY AIR WILL SHOULDER ITS WAY IN AROUND TAU 48,
HELPING TO INCREASE THE PACE OF WEAKENING. HOWEVER, BY THE END OF
THE FORECAST, AS THE SYSTEM MOVES NORTHWARD, SHEAR IS EXPECTED TO
DECREASE, DEEP-LAYER MOISTURE WILL INCREASE AS WILL SSTS AND THE
SYSTEM COULD BEGIN TO RECOVER BY TAU 120. DUE TO THE SMALL NATURE
OF THE SYSTEM, SIGNIFICANT AND RAPID CHANGES IN INTENSITY ARE
LIKELY AS THE INNER-CORE WILL BE HIGHLY SUSCEPTIBLE TO SMALL-SCALE
CHANGES IN THE ENVIRONMENT.   

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE ARE
ARRAYED IN A DREADED SQUASHED-SPIDER ORIENTATION, DENOTING
EXTREMELY HIGH UNCERTAINTY. THE GFS AND GEFS ARE BOTH TRACKING THE
SYSTEM SOUTH FOR ABOUT 24 HOURS THEN LOOP IT BACK NORTH THEN
NORTHWEST BY THE END OF THE FORECAST. THE ECMWF, ECENS, EGRR AND
GOOGLE DEEP MIND ON THE OTHER HAND DEPICT A SOUTHWESTWARD TRACK FOR
12 HOURS, THEN EASTWARD AND EVENTUALLY A TURN TO THE NORTH, BUT
VARY SIGNIFICANTLY ON THE SPEED OF ADVANCE EASTWARD AND THE TIMING
OF THE TURN, LEADING TO A LARGE EAST-WEST SPREAD IN THE TRACKERS.
THE ECMWF-AIFS IS TH EASTERNMOST OUTLIER, TAKING THE SYSTEM ON A
SLOW NORTHEASTWARD ARC AFTER TAU 48, HEADING BACK TOWARDS SUMATRA.
ENSEMBLE GUIDANCE IS LITERALLY ALL OVER THE PLACE, WITH INDIVIDUAL
MEMBERS SPREAD ACROSS THE BULK OF THE SOUTHERN INDIAN OCEAN,
EFFECTIVELY PROVING VERY UNHELPFUL AT THIS POINT. THE JTWC FORECAST
IS POSITIONED CLOSE CONSENSUS MEAN AND ECMWF THROUGH THE FORECAST
PERIOD BUT CONFIDENCE IS VERY LOW DUE TO WIDELY SPREAD DETERMINISTIC
MODELS AND HIGHLY UNCERTAIN ENSEMBLE GUIDANCE. INTENSITY GUIDANCE
ON THE OTHER HAND IS IN GOOD AGREEMENT, WITH MINIMAL SPREAD BETWEEN
THE MODELS. THE JTWC FORECAST IS PLACED NEAR THE CONSENSUS MEAN
WITH HIGH CONFIDENCE. 

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