WDXS31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.5S 89.3E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 620 NM SOUTHWEST OF THE COCOS ISLANDS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SYMMETRICAL CENTRAL DENSE OVERCAST (CDO) WITH A COMPACT EYE FEATURE
ASSOCIATED WITH TROPICAL CYCLONE (TC) 27S (COURTNEY). AS THE SYSTEM
IS TRANSITING SOUTHWESTWARD ALONG THE NORTHWESTERN PERIPHERY OF A
STR TO THE SOUTHEAST, IT IS SHOWING SIGNS OF SLIGHT WEAKENING. 
ANALYSIS REVEALS THAT THE SYSTEM REACHED ITS PEAK OF 130-135 KTS
WITHIN THE LAST 6-12 HOURS. OVER THE LAST TWO HOURS HOWEVER, THE
EYE HAS BEEN CONTRACTING, COOLING AND BEGINNING TO FILL. EYE
TEMPERATURE IS CURRENTLY ANALYZED AT -24 C, WHICH IS OVER 30
DEGREES COOLER THAN 12 HOURS AGO. THE ENVIRONMENTAL ANALYSIS
REVEALS FAVORABLE CONDITIONS, WITH LOW (5-10 KTS) VERTICAL WIND
SHEAR (VWS), MODERATELY WARM (26-27 C) SEA SURFACE TEMPERATURES
(SST), GOOD RADIAL OUTFLOW, AS WELL AS GOOD AMOUNT OF MONSOONAL,
DEEP-LAYER MOISTURE. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE SMALL EYE FEATURE PRESENT IN THE EIR
IMAGERY LOOP, CONSISTENT WITH THE MICROWAVE EYE VISIBLE IN THE
291753Z GMI 37 GHZ IMAGE. TC COURTNEY CONVECTIVE STRUCTURE IN THIS
MICROWAVE IMAGE HINTS AT THE INCOMPLETE EYEWALL REPLACEMENT CYCLE 
(ERC), WHICH IS ALSO INDICATED BY MUCH LOWER (10-15 PERCENT) M-PERC 
ERC PROBABILITY FROM CIMSS, AS COMPARED TO THE ONE FROM 12 HOURS AGO.
THE INITIAL INTENSITY OF 125 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE SLIGHT WEAKENING TREND INDICATED BY THE AGENCY DVORAK
ESTIMATES LISTED BELOW, AS WELL AS THE OBJECTIVE FIXES FROM ADT,
AIDT AND D-PRINT ALL OSCILLATING AROUND 125 KTS.

INITIAL WIND RADII BASIS: 291513 METOP-C ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   KNES: T6.5 - 127 KTS
   DEMS: T7.0 - 140 KTS 
   FMEE: T7.0 - 140 KTS 
   FIMP: T7.0 - 140 KTS 
   CIMSS ADT: 127 KTS AT 291815Z
   CIMSS AIDT: 124 KTS AT 291715Z
   CIMSS D-PRINT: 123 KTS AT 291715Z

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: HIGH

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
SOUTHWESTWARD, AS IT APPROACHES THE AXIS OF A STR TO THE SOUTHEAST.
THE ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN MARGINALLY
FAVORABLE OVER THE NEXT 18-24 HOURS, WITH THE EXCEPTION OF COOLING
SST, AS THE SYSTEM TRACKS POLEWARD. AT THE SAME TIME, BY TAU 24, VWS
WILL BEGIN TO SIGNIFICANTLY INCREASE, EXCEEDING 25 KTS, WHICH
COMBINED WITH COOL (24-25 C) SST AND INCREASING DRY AIR ENTRAINMENT
FROM THE NORTH, WILL CREATE A MUCH MORE HOSTILE ENVIRONMENT, LEADING
TO A CONTINUOUS WEAKENING OF THE SYSTEM. ADDITIONALLY, COAMPS-TC
EPS INTENSITY IS HINTING AT MODERATE TO RAPID WEAKENING OUT TO TAU
48. AFTERWARDS, TC 27S IS FORECAST TO BEGIN TRANSITIONING INTO A
SUBTROPICAL SYSTEM, AS ITS STRUCTURE SHALLOWS OUT, DUE TO
DRASTICALLY INCREASING VWS. STRONG LOW-LEVEL RIDGE TO THE SOUTH
WILL THEN CAUSE TC COURTNEY TO SLOW DOWN AND THEN BE STEERED
WESTWARD. THE SYSTEM IS FORECAST TO DISSIPATE BY TAU 96, PRIOR TO 
COMPLETION OF THE SUBTROPICAL TRANSITION.

MODEL DISCUSSION: SHORT TERM NUMERICAL MODEL TRACK GUIDANCE IS IN
GOOD AGREEMENT, WITH ALL GUIDANCE PREDICTING STORM MOVEMENT ALONG
THE PERIPHERY OF A STR AND JTWC TRACK FORECAST ASSESSED WITH HIGH
CONFIDENCE. CROSS-TRACK SPREAD PRIOR TO THE SYSTEM SLOWING DOWN AT
TAU 48 IS 100 NM, WITH ONLY NAVGEM SHOWING A FASTER MOVEMENT,
LEADING TO THE SYSTEM GOING FURTHER EAST. AFTER TAU 48, ALL
REMAINING GUIDANCE DEPICTS TC COURTNEY TRACKING WESTWARD, BUT THE
FORECAST ENVELOPE INCREASES TO A CROSS-TRACK SPREAD OF A 150 NM BY
THE END OF THE FORECAST PERIOD. ALONG-TRACK SPREAD BY TAU 96 IS
OVER 220 NM, EXCLUDING NAVGEM, RESULTING IN A MEDIUM CONFIDENCE OF THE 
LONG TERM TRACK FORECAST. INTENSITY GUIDANCE IS IN FAIR AGREEMENT, 
WITH ALL OF THE MULTI-MODEL CONSENSUS MEMBERS INDICATING STEADY 
WEAKENING THROUGHOUT THE FORECAST PERIOD. HOWEVER, THE DISSIPATION 
TIMELINE RANGES BETWEEN TAU 60 AND 96, RESULTING IN MEDIUM INTENSITY 
FORECAST CONFIDENCE ASSESSMENT. JTWC INTENSITY FORECAST IS SET 
SLIGHTLY ABOVE THE CONSENSUS MEAN AND CLOSE TO THE HAFS-A GUIDANCE.

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