WDXS31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1S 88.3E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 727 NM SOUTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 27S (COURTNEY) WITH A FILLED EYE AND RAPIDLY WEAKENING
CONVECTION OVER THE DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC).
THE CONVECTION IS NOW ALSO BECOMING DISPLACED SLIGHTLY TO THE SOUTH
OF THE LLCC AS THE SYSTEM WEAKENS. DRY AIR CAN BE SEEN BEGINNING TO
ENTRAIN INTO THE SYSTEM ALONG THE NORTHERN PERIPHERY. ENVIRONMENTAL
ANALYSIS INDICATES THAT 27S IS IN A MARGINAL ENVIRONMENT THAT WILL
ONLY WORSEN IN THE NEXT COUPLE DAYS. CURRENT ENVIRONMENTAL
PARAMETERS INCLUDE STRONG POLEWARD OUTFLOW, LOW (10-15 KTS)
VERTICAL WIND SHEAR, WARM (26-27 C) SEA SURFACE TEMPERATURES, AND
DRY AIR TO THE NORTH. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE PARTIALLY EXPOSED LOW-LEVEL CLOUD LINES IN
THE ANIMATED MSI. THE INITIAL INTENSITY OF 100 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE AND OBJECTIVE BEST TRACK

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST-SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   FMEE: T5.0 - 90 KTS
   FIMP: T6.0 - 115 KTS
   CIMSS SATCON: 88 KTS AT 300615Z
   CIMSS ADT: 97 KTS AT 300615Z
   CIMSS AIDT: 90 KTS AT 300615Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT WITHIN THE NORTHERN
SEMICIRCLE

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: A QUICKER WEAKENING TREND THAN
PREVIOUSLY FORECASTED

FORECAST DISCUSSION: TC 27S IS FORECAST TO TRACK GENERALLY
SOUTHWARD THROUGH TAU 48 AS IT CONTINUES TO ROUND THE STR TO THE
EAST. AFTER TAU 48, THE VORTEX WILL BECOME VERY SHALLOW AND IS THEN
EXPECTED TO TURN WESTWARD, AS THE STEERING MECHANISM TRANSITIONS TO
A LOW-LEVEL RIDGE THAT WILL BE POSITIONED TO THE SOUTH. REGARDING
INTENSITY, 27S IS FORECAST TO RAPIDLY WEAKEN OVER THE NEXT 36 HOURS
TO AN INTENSITY OF AROUND 45 KTS AS THE SYSTEM ENTERS SUB 25 C
WATERS, SHEAR RAISES TO ABOVE 40 KTS, AND DRY AIR DECAPITATES THE
VORTEX. AFTER TAU 36, POLEWARD OUTFLOW WILL GREATLY INCREASE DUE TO
THE POSITION OF THE VORTEX RELATIVE TO THE JET, WHICH WILL ALLOW
FOR A MORE GRADUAL WEAKENING THROUGH TAU 72, WHERE THE SYSTEM IS
FORECAST TO DROP BELOW 35 KTS. SUBTROPICAL TRANSITION IS ALSO
LIKELY TO COMPLETE NEAR THE SAME TIME AS DISSIPATION AND THE SYSTEM
BEGINS TO INTERACT WITH THE JET AND THE VORTEX BECOMES VERY
SHALLOW.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 27S WITH A 65 NM CROSS-TRACK SPREAD AT TAU
48 AND A 130 NM CROSS-TRACK SPREAD AT TAU 72. THE JTWC TRACK
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL
MODELS DEPICTING RAPID WEAKENING THROUGH TAU 36 AND A MORE GRADUAL
WEAKENING TREND THEREAFTER. THE JTWC INTENSITY FORECAST IS ALSO
PLACED WITH HIGH CONFIDENCE AS A RESULT.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: HIGH//
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