WDXS31 PGTW 280900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 95.5E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 288 NM SOUTH-SOUTHWEST OF THE COCOS
ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN
ASYMMETRIC AND POORLY ORGANIZED REGION OF MODERATE CONVECTION,
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). CLOUD TOP
TEMPERATURES HAVE WARMED SIGNIFICANTLY OVER THE PAST SIX HOURS AND
THE DEEPEST CONVECTION IS NOW FORMED INTO A BEAN SHAPE, WITH THE
ASSESSED LLCC LOCATED IN THE SOUTHERN PORTION OF THE CONVECTIVE
MASS. WHILE THE DEPICTION IS THE MSI IS NOT GREAT, A 280310 COWVR
34GHZ MICROWAVE IMAGE REVEALS A WELL-DEFINED LOW-LEVEL STRUCTURE,
WITH A MICROWAVE EYE FEATURE AND SYMMETRIC BANDS OF CONVECTION
WRAPPING INTO THE WELL-DEFINED CENTER. A NEARLY COINCIDENT AMSU-B
89GHZ IMAGE REVEALS A SIMILAR STORY, THOUGH COMPARISON OF THE TWO
FREQUENCIES REVEALS A MODEST AMOUNT OF VORTEX TILT TO THE WEST WITH
HEIGHT. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE,
EXTRAPOLATING FROM THE MICROWAVE EYE IN THE COWVR IMAGE. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED HIGHER 
THAN ALL OF THE OBJECTIVE ESTIMATES WHICH HAVE BEEN RUNNING LOW FOR
THE DURATION OF THE SYSTEM, HEDGED TOWARDS THE SUBJECTIVE FIXES AND
IN LINE WITH AN EARLIER RCM-1 SAR PASS. THE ENVIRONMENT IS
FAVORABLE FOR FURTHER INTENSIFICATION, WITH LOW DEEP-LAYER WIND
SHEAR, WARM SSTS AND GOOD RADIAL OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T4.5 - 77 KTS
   APRF: T4.5 - 77 KTS
   CIMSS SATCON: 61 KTS AT 280700Z
   CIMSS ADT: 59 KTS AT 280540Z
   CIMSS AIDT: 63 KTS AT 280540Z
   CIMSS D-PRINT: 52 KTS AT 280700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: LOCALIZED RADIAL OUTFLOW IN PROXIMITY TO THE
STORM ITSELF. 

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 27S IS FORECAST TO SLOWLY ARC OVER TO A
MORE WEST-SOUTHWEST TRACK OVER THE NEXT FEW HOURS AS THE RIDGE
CENTER MOVES FROM ITS CURRENT POSITION DUE SOUTH OF TC 27S, TO A
POSITION TO THE SOUTHEAST. BY TAU 72, TC 27S WILL HAVE ROUNDED THE
RIDGE AXIS AND BE TRACKING DUE SOUTH, THOUGH TRACK SPEEDS WILL SLOW
DOWN AS IT RUNS HEADLONG INTO A LOW- TO MID-LEVEL RIDGE TO THE
SOUTH. IN TERMS OF INTENSITY, UPPER-LEVEL WINDS ARE SPLITTING AND
GOING AROUND THE SYSTEM BASED ON THE LATEST CIMSS ATMOSPHERIC
MOTION VECTOR (AMV) AND CIRA UPPER-LEVEL DERIVED MOTION WIND
ANALYSIS. THIS HAS LOWERED THE SHEAR IN VICINITY OF THE SYSTEM,
WHICH SHOULD ALLOW FOR A SHORT PERIOD OF INTENSIFICATION
IMMINENTLY. BUT THE SYSTEM ONLY HAS ABOUT 36 TO 48 HOURS OF
FAVORABLE CONDITIONS, BEFORE THE ENVIRONMENT RAPIDLY TURNS HOSTILE.
NORTHWESTERLY SHEAR IS FORECAST TO RAPIDLY INCREASE AFTER TAU 48,
WHICH WILL ALSO BE AROUND THE TIME THE SYSTEM CROSSES THE 26C
ISOTHERM, THE ONE-TWO PUNCH OF SHREDDING THE VORTEX FROM ABOVE AND
THE LOSS OF THE ENERGY SOURCE WILL MARK THE BEGINNING OF A RAPID
WEAKENING PHASE. DRY AIR USHERED IN ON THE STRONG NORTHWESTERLY
SHEAR, WILL INTRUDE INTO THE CORE OF THE SYSTEM AFTER TAU 72,
ACCELERATING THE ALREADY RAPID WEAKENING. THE SYSTEM FALLS TO WEAK
TROPICAL STORM STRENGTH BY TAU 96 AND AS IT CONTINUES TO WEAKEN AND
DISSIPATE, THE STEERING LEVEL WILL STEADILY LOWER. STRONG
SOUTHEASTERLY FLOW ASSOCIATED WITH A LOW- TO MID-LEVEL RIDGE TO THE
SOUTH WILL TAKE OVER STEERING AFTER TAU 96 AND PUSH THE REMNANT
VORTEX OFF TO THE WEST BY TAU 120. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN TIGHT
AGREEMENT THROUGH THE FIRST THREE DAYS OF THE FORECAST, WITH THE
GUIDANCE ENVELOPE GRADUALLY EXPANDING TO ABOUT 150NM BY TAU 72. GFS
CONTINUES TO TAKE THE INSIDE TRACK, WHILE THE ECMWF-AIFS SHOWS A
MORE GRADUAL TURN SOUTHWARD, MARKING THE WESTERN EDGE OF THE
ENVELOPE. THROUGH TAU 72, THE JTWC FORECAST ALIGNS WITH THE
CONSENSUS MEAN AND THE ECMWF DETERMINISTIC TRACKER WITH HIGH
CONFIDENCE. AFTER TAU 72, QUICKLY FANS OUT TO OVER 400NM BETWEEN
THE GFS TO THE EAST AND THE UKMET ENSEMBLE TO THE WEST. ALTHOUGH
ALL MODELS AGREE THAT THE SYSTEM WILL TURN SHARPLY WESTWARD AROUND
TAU 96, THEY DIFFER ON THE EXACT TIMING AND THE POST-TURN SPEED OF
THE REMNANT VORTEX, HENCE THE WIDE DIVERGENCE IN ULTIMATE TAU 120
POSITION. THE JTWC FORECAST IS POSITIONED CLOSE TO THE CONSENSUS
MEAN WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS OVERALL IN GOOD
AGREEMENT ON THE GENERAL SHAPE OF THE INTENSITY TREND, AND ONLY A
10-KNOT SPREAD IN PEAK INTENSITY, BETWEEN 80-90 KNOTS. THE JTWC
FORECAST IS PLACED ON TOP OF THE HAFS-A GUIDANCE WITH HIGH
CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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