WDXS32 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (GRANT) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.8S 97.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 48 NM EAST-NORTHEAST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 09S (GRANT) HAS DISPLAYED A HIGHLY CYCLICAL
NATURE OVER THE PAST COUPLE OF DAYS, WITH EPISODIC BURSTS OF
CONVECTION FOLLOWED BY CONVECTIVE DISSIPATION AND ENHANCED
NORTHEASTERLY SHEAR. THE SATELLITE LOOP OVER THE PAST SIX HOURS
INDICATES WE ARE IN THE MIDST OF ANOTHER DISSIPATION CYCLE AT THE
CURRENT MOMENT. AND VERY SIMILAR TO 24 HOUR AGO, THE LOW-LEVEL
CIRCULATION CENTER (LLCC) HAS BECOME CHALLENGING TO LOCATE AS THE
CONVECTIVE MOVES AWAY TO THE SOUTH AND LEAVES BEHIND STRONG
MID-LEVEL ROTATION, WHICH OBSCURES THE LLCC. TWO RECENT MICROWAVE
PASSES (A 121157Z SSMIS AND A 121146Z WSF-M) WERE FAIRLY DISSIMILAR
IN DEPICTING THE STRUCTURE OF TC 09S, AND DID NOT PROVIDE MUCH
CLARITY TO THE ANALYSIS. THE SSMIS 91GHZ IMAGE LINED UP CLOSEST
WITH WHAT WAS SEEN IN THE EIR LOOP, AND THE INITIAL POSITION WAS
PLACED WITH LOW CONFIDENCE ON THE NORTHERN EDGE OF THE DEEP
CONVECTION WHICH AT THAT TIME WAS JUST STARTED TO PUSH OFF TO THE
SOUTH. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON AN AVERAGE OF THE OBJECTIVE AND SUBJECTIVE INTENSITY
ESTIMATES OUTLINED BELOW. THE ENVIRONMENT IS MARGINALLY FAVORABLE,
WITH LOW (10-15 KNOTS) NORTHEASTERLY VWS, WEAK POLEWARD AND
WESTWARD OUTFLOW AND WARM SSTS. DRY AIR REMAINS A CONCERN, WITH THE
TPW LOOP SHOWING A WEDGE OF DRY MID-LEVEL AIR PUSHING UP FROM THE
SOUTH ALONG THE WESTERN FLANK OF THE SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN, WITH A
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTHWEST AND A STR
POSITIONED TO THE SOUTHEAST AND A WEAK TROF TO THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   APRF: T2.0 - 30 KTS
   CIMSS SATCON: 41 KTS AT 241208Z
   CIMSS ADT: 51 KTS AT 241130Z
   CIMSS AIDT: 38 KTS AT 241230Z
   CIMSS D-MINT: 36 KTS AT 241208Z
   CIMSS D-PRINT: 37 KTS AT 241230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TC 09S HAS BEEN MOVING NORTHWESTWARD AT A SLOW
PACE OVER THE PAST 12 HOURS, AND THIS MOTION IS EXPECTED TO
CONTINUE FOR THE NEXT 12 TO 24 HOURS, AS THE STEERING PATTERN
REMAINS RELATIVELY WEAK, WITH COMPETING INFLUENCES FROM MULTIPLE
RIDGES AND A COL REGION TO THE SOUTH. THE TRACK WILL FLATTEN OUT BY
TAU 36 AND THEN QUICKLY SHIFT TO A SOUTHWESTWARD TRAJECTORY AS THE
RIDGE TO THE SOUTHEAST BEGINS TO BUILD AND STRENGTHENS THE STEERING
GRADIENT. TC 09S WILL BEGIN TO ACCELERATE AFTER TAU 48, WHILE
CONTINUING ON A SOUTHWESTWARD TRACK THROUGH THE REMAINDER OF THE
FORECAST PERIOD AS THE STR CONTINUES TO BUILD AND MOVES SOUTHWEST
ALONG WITH TC 09S. INTENSITY PRESENTS A BIT TRICKIER OF A
PROPOSITION, ESPECIALLY WITH THE COMPACT NATURE OF THE SYSTEM AND
THE HIGHLY CYCLICAL NATURE OF THE CONVECTION SEEN OVER THE PAST
COUPLE OF DAYS. IN THE NEAR TERM, AVAILABLE MODEL GUIDANCE
INDICATES A SLIGHT IMPROVEMENT IN THE ENVIRONMENT IS EXPECTED, WITH
DECREASING SHEAR AND INCREASED MOISTURE. THIS WILL ALLOW TC 09S TO
INTENSIFY OVER THE NEXT 24 TO 36 HOURS, THOUGH THE EXPECTED PEAK
INTENSITY CONTINUES TO DECREASE, NOW EXPECTED TO BE 60 KNOTS. AFTER
TAU 36, NORTHEASTERLY SHEAR WILL INCREASE, WHILE DRY AIR WILL MOVE
IN FROM THE NORTH AS WELL, INITIATING A WEAKENING PHASE, WHICH IS
EXPECTED TO CONTINUE THROUGH TAU 72. AFTER TAU 72, CONDITIONS LOOK
TO IMPROVE ONCE AGAIN, AND TC 09S WILL RE-INTENSIFY THROUGH THE
REMAINDER OF THE FORECAST PERIOD.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
ON THE TRACK SCENARIO. THE GFS IS POSITIONED ON THE NORTHERN EDGE
OF THE ENVELOPE, WHILE THE ECMWF IS ON THE SOUTH EDGE, WITH THE
CROSS-TRACK SPREAD INCREASING TO 75NM AT TAU 72, AND 125NM AT TAU
120. MULTI-MODEL ENSEMBLE GUIDANCE IS IN STRONG AGREEMENT AS WELL,
WITH ALL MEMBERS OF BOTH THE GEFS AND ECEPS SHOWING A SHALLOW
NORTHWESTWARD TRACK IN THE NEAR-TERM FOLLOWED BY A SOUTHWESTWARD
TRACK THROUGH THE END OF THE FORECAST PERIOD. THE AI ENSEMBLE
MODELS (EC-AIFS AND GDM FNV3) SHOW A BIT MORE UNCERTAINTY COMING
INTO PLAY AT THE END OF THE FORECAST PERIOD WITH SOME MEMBERS
BEGINNING TO TURN POLEWARD, BUT THE VAST MAJORITY STICK TO THE
SOUTHWESTWARD TRAJECTORY THROUGH THE FORECAST. THE JTWC FORECAST IS
POSITIONED NEAR THE CONSENSUS MEAN AND THE ECENS MEAN TRACKERS WITH
HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN FAIRLY GOOD AGREEMENT,
WITH ALL MEMBERS OF THE CONSENSUS SHOWING A WAVE-LIKE TRACE OF
NEAR-TERM INTENSIFICATION, THEN WEAKENING, FOLLOWED BY
RE-INTENSIFICATION IN THE LONG-RANGE FORECAST. ALL MODELS INDICATE A
PEAK BETWEEN 45-60 KNOTS BETWEEN TAU 24 AND TAU 36 (EXCEPT FOR THE
RIDE AND CTR1 RAPID INTENSIFICATION AIDS WHICH DEPICT THE SYSTEM
REACHING 70-75 KNOTS) AND A LOW-POINT BETWEEN 40-50 KNOTS BY TAU
72. THE MODELS GET A BIT AGGRESSIVE IN THE LONG-TERM, WITH NEARLY
ALL INDICATING RI AFTER TAU 96, WITH THE HAFS-A REACHING 120 KNOTS
BY TAU 120. THE HYPER-AGGRESSIVE HAFS-A IS PULLING THE CONSENSUS
MEAN UP TO UNREALISTIC LEVELS BY THE END OF THE FORECAST AS WELL.
THE JTWC FORECAST IS PLACED CLOSE TO THE MEAN THROUGH TAU 96, AND
THE GFS DETERMINISTIC TRACKER THROUGH TAU 120. 

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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