WDXS32 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (NINE) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.2S 108.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 657 NM EAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE AND ANIMATED SHORTWAVE
INFRARED SATELLITE IMAGERY DEPICTS A COMPACT AND NOW FULLY OBSCURED
LOW LEVEL CIRCULATION CENTER (LLCC). OVER THE PAST 12 HOURS, THE
LLCC HAS MOVED WEST, TUCKED UNDER THE EDGE OF MODERATE CONVECTION
WHICH DEVELOPED EARLIER IN THE DAY, THEN PERFORMED A CLOCKWISE
LOOP, EMERGING INTO THE CLEAR AROUND 1000Z BEFORE ONCE MORE MOVING
UNDER THE CURRENTLY DEVELOPING CONVECTION. THE RECENT CONVECTIVE
BURST IS PRIMARILY FOCUSED ON THE WESTERN FLANK OF THE CIRCULATION,
WHERE THE PREVIOUS CONVECTIVE BURST HAVE DEVELOPED, AND EXHIBITS A
SHARP EASTERN EDGE INDICATIVE OF THE PRESENCE OF MODERATE EASTERLY
SHEAR. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON MULTIPLE AGENCY FIX POSITIONS AND TRACKING OF THE LLCC OVER
TIME. THE INITIAL INTENSITY IS MAINTAINED AT 35 KNOTS WITH MEDIUM
CONFIDENCE, BASED ON AN AVERAGE OF THE AGENCY CURRENT INTENSITY
ESTIMATES OF T2.5-T3.0 AND THE OBJECTIVE ESTIMATES NOTED BELOW.
EARLIER SCATTEROMETER PASSES REVEALED WINDS GENERALLY BELOW 35
KNOTS, BUT WITH THE REINVIGORATION OF CONVECTION, IF THE SYSTEM DID
DIP BELOW 35 KNOTS, IT IS LIKELY BACK AT 35 KNOTS AT THIS POINT IN
TIME. ENVIRONMENTAL CONDITIONS REMAIN MARGINAL, WITH MODERATE
EASTERLY SHEAR, WEAK WESTWARD OUTFLOW ALOFT AND WARM SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
LOW-LEVEL NEAR EQUATORIAL RIDGE (NER) OVER BORNEO AND A LOW-LEVEL
SUBTROPICAL RIDGE (STR) WEST OF AUSTRALIA.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T2.5 - 35 KTS
   CIMSS ADT: 35 KTS AT 191130Z
   CIMSS AIDT: 33 KTS AT 191130Z
   CIMSS D-PRINT: 29 KTS AT 191230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK WESTWARD
   OTHER FACTORS: DRY MID-LEVEL AIR ALONG THE EASTERN FLANK. 

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) 09S (NINE) IS CURRENTLY
MEANDERING IN A CLOCKWISE LOOP, CAUGHT IN A RELATIVELY WEAK
STEERING PATTERN WITH RIDGING IN THE LOWER-LEVELS BOTH TO THE NORTH
AND SOUTH. HOWEVER, OVER THE NEXT 12 TO 24 HOURS, THE RIDGE TO THE
NORTH IS FORECAST TO WEAKEN WHILE RIDGING TO THE SOUTH BUILDS,
WHICH WILL ALLOW TC 09S TO BEGIN TRACKING WESTWARD. THE SYSTEM THEN
TRACKS WESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD, ALONG
THE NORTHERN SIDE OF A SUBTROPICAL RIDGE (STR) COMPLEX TO THE
SOUTH. TRACK SPEEDS WILL BE RELATIVELY SLOW, DUE TO DEVELOPMENT OF
A TROF OR AREA OF LOW HEIGHTS ALOFT WHICH STAYS WEST OF AUSTRALIA
THROUGH THE FORECAST PERIOD, INDUCING A SLIGHT WEAKNESS IN THE RIDGE
SOUTH OF TC 09S, KEEPING THE STEERING GRADIENT WEAKER THAN IT MIGHT
OTHERWISE BE. SOME MODELS, INCLUDING THE GFS AND HWRF, SHOW TC 09S
BEING CAUGHT BY THIS TROF AND MOVING POLEWARD AFTER TAU 48, WHILE
THE ECMWF, HAFS-A AND MOST OF THE ENSEMBLES KEEP THE SYSTEM MOVING
WEST AND NOT BEING CAUGHT BY THE TROF. IN TERMS OF INTENSITY, SHEAR
IS ALREADY DECREASING, DOWN ABOUT 10 KNOTS FROM YESTERDAY AND THE
ATMOSPHERE IS MOISTENING UP. BUT THE VORTEX REMAINS HIGHLY TILTED
AND WILL TAKE SOME TIME TO ALIGN. INTENSITY IS THUS EXPECTED TO
REMAIN FLAT, OR EVEN BRIEFLY DIP DOWN TO 30 KNOTS, OVER THE NEXT 24
HOURS. BY TAU 36, THE VORTEX SHOULD BE ALIGNED, AND SHEAR WILL BE
LOW, ALLOWING FOR THE SYSTEM TO BEGIN INTENSIFYING. A PEAK OF
AROUND 70 KNOTS IS EXPECTED AROUND TAU 84 BEFORE SHEAR BEGINS TO
INCREASE AND DRY AIR MOVES IN FROM THE NORTHWEST, MARKING THE
BEGINNING OF THE WEAKENING PHASE. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GENERALLY GOOD
AGREEMENT. THE BULK OF THE GUIDANCE SHOWS A TRACK WESTWARD TOWARDS
COCOS ISLAND, WITH A CROSS-TRACK SPREAD OF ABOUT 130NM BETWEEN THE
ECMWF TO THE NORTH AND THE GEFS MEAN TO THE SOUTH. ALONG-TRACK
SPREAD INCREASES TO ABOUT 120NM WITHIN THIS GROUPING OF MODELS,
WITH THE ECMWF-AIFS BEING THE FASTEST MODEL AND NAVGEM THE SLOWEST.
MEANWHILE, THE GFS AND HWRF SHOW THE SYSTEM GETTING CAUGHT BY THE
TROF TO THE SOUTH AND TURNING POLEWARD AFTER TAU 48, SEPARATING
FROM THE REMAINDER OF THE GUIDANCE. MULTI-MODEL ENSEMBLE GUIDANCE
STRONGLY SUPPORTS A WESTWARD TRACK, WITH JUST A FEW MEMBERS
DEPICTING A POLEWARD TRAJECTORY. THE JTWC FORECAST IS POSITIONED
CLOSE TO THE MULTI-MODEL DETERMINISTIC AND ENSEMBLE CONSENSUS
MEANS, WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS MORE MIXED, WITH
THE CTCX SHOWING LITTLE TO NO INTENSIFICATION BEFORE WEAKENING
AFTER TAU 48, WHILE THE HWRF PEAKS AROUND 85 KNOTS AND THE HAFS-A
AT 105 KNOTS BETWEEN TAU 72 AND TAU 96. THE HAFS-A HAS BEEN
PERSISTENT IN FORECASTING A VERY STRONG TC, BUT IS LIKELY OVERDOING
IT. THE JTWC FORECAST IS PLACED NEAR THE SHIPS, GFS DETERMINISTIC
AND CONSENSUS MEAN, WITH MEDIUM CONFIDENCE. 

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