WDXS31 PGTW 282100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4S 93.0E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 385 NM SOUTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 44 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PINHOLE EYE SURROUNDED BY A NEARLY SYMMETRICAL, COMPACT OUTFLOW
BOUNDARY OF TROPICAL CYCLONE (TC) 27S (COURTNEY). THE INITIAL
POSITION IS THEREFORE PLACED WITH HIGH CONFIDENCE BASED ON THE SMALL 
(5-10 NM DIAMETER) EYE FEATURE. 281531Z METOP-C AMSUB 89 GHZ PASS 
SHOWS A SYMMETRICAL MICROWAVE EYE AND CONVECTIVE STRUCTURE, WITH 
SLIGHTLY STRONGER BANDING OVER THE WESTERN SEMICIRCLE. ANALYSIS 
REVEALS FAVORABLE ENVIRONMENTAL CONDITIONS WITH LOW (5-10 KTS) DEEP-
LAYER VERTICAL WIND SHEAR (VWS), WARM (26-27 C) SEA SURFACE 
TEMPERATURES (SST) AND GOOD RADIAL OUTFLOW. THE INITIAL INTENSITY OF 
115 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON DVORAK ESTIMATES 
LISTED BELOW. OBJECTIVE ESTIMATES ARE STILL CATCHING UP TO THE AGENCY
FIXES, WHILE SWITCHING BETWEEN EYE AND UNIFORM SCENES, WITH RAW T-
NUMBER VALUES RANGING BETWEEN 6.2 AND 4.5 ACCORDINGLY.

INITIAL WIND RADII BASIS: 281442Z METOP-B ASCAT IMAGE

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR)
CENTERED TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   APRF: T5.5 - 102 KTS
   CIMSS SATCON: 91 KTS AT 281705Z
   CIMSS ADT: 92 KTS AT 281830Z
   CIMSS AIDT: 91 KTS AT 281830Z
   CIMSS D-PRINT: 94 KTS AT 281900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 CONTINUE TRACKING ALONG
THE NORTHWESTERN PERIPHERY OF A STR TO THE SOUTHEAST, WHILE
MAINTAINING INTENSITY FOR THE NEXT 6 TO 12 HOURS. THE SYSTEM IS
CURRENTLY ENCAPSULATED WITHIN A BROAD AREA OF DRY AIR, BUT GIVEN
ITS COMPACT NATURE, IT WILL BE AT LEAST 48 HOURS UNTIL THE DRY AIR
STARTS TO GET ENTRAINED WITHIN THE CORE OF THE VORTEX. AT THE SAME
TIME, AN UPPER-LEVEL TROUGH IS EXPECTED TO PASS TO THE SOUTH OF THE
SYSTEM AROUND TAU 48, POTENTIALLY BRIEFLY IMPROVING THE OUTFLOW.
AFTER TAU 48, TC 27S IS EXPECTED TO ROUND THE AXIS OF THE RIDGE AND
TURN SOUTHEASTWARD. AT THE SAME TIME, AS THE SYSTEM MOVES SOUTH,
THE SST WILL DECREASE TO 26 C. AT THAT TIME, DRASTICALLY INCREASING 
VWS AND DRY AIR ERODING THE CORE OF THE VORTEX WILL LEAD TO RELATIVELY 
QUICK WEAKENING. AROUND TAU 72, TC 27S IS FORECAST TO BEGIN 
TRANSITIONING INTO A SUBTROPICAL SYSTEM, AS ITS STRUCTURE
SHALLOWS. THE LOW-LEVEL EASTERLY FLOW, ASSOCIATED WITH A STRONG
RIDGE TO THE SOUTH, WILL THEN STEER THE SYSTEM WESTWARD. TC COURTNEY 
IS FORECAST TO COMPLETE DISSIPATION BY TAU 120, BEFORE IT COMPLETES 
THE SUBTROPICAL TRANSITION.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGH THE INITIAL 48 HOURS, WITH A 100 NM CROSS-TRACK
SPREAD AND 65 NM ALONG-TRACK SPREAD. THE ONLY OUTLIER WITHIN THE
CONSENSUS MEMBER GROUP IS UKMET ENSEMBLE, WHICH PREDICTS A WESTWARD
TURN AT TAU 72, WHILE THE REMAINDER OF THE GUIDANCE IS STILL ROUNDING
THE AXIS OF THE RIDGE. AT TAU 120, ALL MODEL GUIDANCE INDICATES A
STEERING PATTERN CHANGE, TRACKING THE SYSTEM WESTWARD. CROSS-TRACK
SPREAD, WITH THE EXCLUSION OF UKMET ENSEMBLE REMAINS GOOD AT 75 NM.
MEDIUM OVERALL CONFIDENCE ASSESSMENT OF THE TRACK FORECAST IS
REFLECTED BY THE TRACK LAID CLOSE TO THE MULTI-MODEL CONSENSUS,
OFFSET ONLY FOR THE UKMET ENSEMBLE GUIDANCE. INTENSITY GUIDANCE IS
IN FAIR AGREEMENT THROUGHOUT THE FORECAST AND IS PLACED WITH MEDIUM
CONFIDENCE AS WELL, AND CLOSE TO THE CONSENSUS GUIDANCE. THE INTENSITY 
SPREAD REMAINS WITHIN 15 KTS THROUGHOUT THE FORECAST PERIOD, WITH THE
EXCLUSION OF THE GFS DETERMINISTIC MODEL, WHICH IS DRASTICALLY MORE
AGGRESSIVE IN REGARD TO THE INITIAL WEAKENING TREND. AFTER TAU 72,
GFS ESTIMATES GET WITHIN THE SAME UNCERTAINTY SPREAD AS OTHER MODELS. 
ALL AVAILABLE NUMERICAL MODEL GUIDANCE MEMBERS INDICATE DISSIPATION BY 
TAU 120.

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