WDXS31 PGTW 272100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 98.2E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 286 NM SOUTH-SOUTHEAST OF THE COCOS
ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) IMAGERY SHOWS A COMPACT SYSTEM
WITH ENHANCED OUTFLOW FEATURING EXTENSIVE TRANSVERSE BANDING ON THE
EQUATORWARD CHANNEL. THE SOUTHEAST QUADRANT IS EXHIBITING SIGNS OF
SUBSIDENCE DUE TO CONFLUENT FLOW ALOFT, LEADING TO AN INCREASINGLY
ASYMMETRIC SHAPE IN THE EIR BAND. THIS INTERRUPTION IN THE POLEWARD
OUTFLOW HAS STALLED DEVELOPMENT MOMENTARILY, REDUCING THE ASSESSED
INTENSITY BY 5 KTS FROM THE LAST TAU. THIS TREND IS SUPPORTED BY A
SLIGHT DECREASE AMONG THE OBJECTIVE INTENSITY ESTIMATES, WHICH HAVE
BEEN ON THE LOWER END DUE TO THE COMPACT NATURE OF TC 27S. THE
VORTEX IS MAINTAINING A RELATIVELY VERTICAL STACK, AND ALTHOUGH
MESSY IN THE UPPER LEVELS, THE LOW-LEVEL WIND FIELD IS HIGHLY
SYMMETRIC, CIRCULAR, AND CONDENSED. THE INITIAL POSITION AND
INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE DUE TO A 271742Z GMI 
37 GHZ MICROWAVE IMAGE AND COMPARISON TO EARLIER SAR AND NRCS DATA
FROM A BULLSEYE 271151Z SAR PASS, WHICH WAS ALSO USED TO ADJUST
WIND RADII.

INITIAL WIND RADII BASIS: SAR DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T4.5 - 77 KTS
   APRF: T5.0 - 90 KTS
   CIMSS SATCON: 68 KTS AT 271820Z
   CIMSS ADT: 82 KTS AT 271740Z

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: COURTNEY WILL CONTINUE TRACKING WESTWARD AT
CLIMATOLOGICALLY AVERAGE TRACK SPEEDS WITH A GRADUAL CURVE
SOUTHWARD. THE STEERING INFLUENCE WEAKENS BY TAU 72, LEADING TO
SLOWING TRACK MOTIONS AND LARGE UNCERTAINTIES IN THE TRACK FORECAST
AFTER TAU 72. GENERALLY SOUTH-SOUTHWESTWARD MOVEMENT IS EXPECTED
THROUGH TAU 120. IN THE SHORT TERM, THE ENVIRONMENT IS FAVORABLE
FOR CONTINUED DEVELOPMENT DUE TO THE EQUATORWARD OUTFLOW CHANNEL,
WARM SEA SURFACE TEMPERATURES (SST), LIGHT VWS, AND SATURATED
MOISTURE FIELD. THE SYSTEM IS EXPECTED TO INTENSIFY SLIGHTLY OVER
THE NEXT 24-36 HOURS, WITH THE CAVEAT THAT IF AN EYE IS ABLE TO
FORM, THE INTENSIFICATION WILL ACCELERATE. HOWEVER, IF AN EYE IS
NOT ABLE TO FORM THE NEAR TERM, THE INTENSITY MAY STAGNATE GOING
FORWARD AND ESSENTIALLY FLATLINE DURING THE SHORT-TERM FORECAST.
BETTER CONFIDENCE SUGGESTS A WEAKENING TREND CAN BE EXPECTED AFTER
TAU 36 AS THE ENVIRONMENT BEGINS TO TRANSITION AWAY FROM FAVORABLE.
DRY AIR WILL BEGIN TO WRAP AROUND THE WEST AND NORTH SIDE AFTER TAU
60, WHICH WILL WORK TO ERODE THE INTEGRITY OF THE VORTEX AT THE
SAME TIME VWS INCREASES. COOLING SSTS WILL BECOME INCREASINGLY
PROBLEMATIC AS THE SYSTEM TURNS SOUTHWARD AND NEARS THE 26C
ISOTHERM IN THE LATER TAUS. A TRANSITION TO AN EXTRATROPICAL
CYCLONE IS LIKELY AFTER TAU 120.


MODEL DISCUSSION: THE TRACK AIDS FOLLOW A TIGHT CORRIDOR WESTWARD
AND AGREE ON THE PLACEMENT AND TIMING OF A SOUTHWARD TURN. THE
OUTLIER IS THE GFS TRACK AIDS, WHICH LIE SOUTH AND EVENTUALLY EAST
OF THE CONSENSUS AS THE OVERALL TRACK CURVES SOUTHWARD, BUT THE
DELTA FROM CONSENSUS IS ONLY UP TO 50 NM BY TAU 72. AFTER TAU 72
AND ESPECIALLY PRONOUNCED AFTER TAU 96, THE TRACK AIDS SPREAD
CONSIDERABLY DUE TO UNCERTAINTIES IN THE STEERING RIDGE STRENGTH
AND SHAPE. ABOUT HALF OF THE TRACK AIDS PREDICT A GENERAL SOUTHWARD
TRAJECTORY, WHILE THE REST INDICATE A SOUTHWESTWARD TRACK. THE JTWC
TRACK FORECAST CLOSELY MATCHES THE CONSENSUS AND THE ECMWF TRACK
AIDS WITH HIGH CONFIDENCE THROUGH TAU 72. THE BULK OF INTENSITY
GUIDANCE SUGGESTS ONLY MODEST INTENSIFICATION CAN BE EXPECTED PRIOR
TO THE TAU 36 WEAKENING POINT. THE OUTLIER IS HAFS, WHICH IS
RAPIDLY INTENSIFYING THE SYSTEM BY TAU 12, THEN HOLDS STEADY UNTIL
WEAKENING AFTER TAU 36. THE JTWC INTENSITY FORECAST ACCOUNTS FOR
THE POSSIBILITY OF EYE FORMATION, AND IS HEDGED ON THE HIGHER SIDE
OF THE CONSENSUS.

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