WDXS31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (COURTNEY) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 100.0E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 330 NM SOUTH-SOUTHEAST OF THE COCOS
ISLANDS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 33 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICT A COMPACT, SLIGHTLY
ASYMMETRIC CONVECTIVE MASS, WITH EMBEDDED OVERSHOOTING TOPS WITH
CLOUD TOP TEMPERATURES AS LOW AS -95C. ANIMATED WATER VAPOR IMAGERY
SHOWS A DIFFUSE UPSHEAR EDGE OF THE CLOUD MASS, SUGGESTIVE OF A
LOCALIZED REDUCTION IN THE OTHERWISE MODERATE EASTERLY SHEAR. AN
ARC OF CIRRUS MARKS THE EASTWARD EXTENT OF THE UPPER-LEVEL OUTFLOW,
WITH SOME RELATIVELY DRIER AIR TO THE WEST OF THE ARC, AN INDICATOR
OF A POTENTIAL PERIOD OF ADDITIONAL, POTENTIALLY RAPID,
INTENSIFICATION WITHIN THE NEXT 12 TO 24 HOURS. A LACK OF RECENT
MICROWAVE IMAGERY PRECLUDES A FULL ANALYSIS OF THE CORE STRUCTURE
OF THE CYCLONE, BUT 270515Z OSCAT-3 SCATTEROMETER PASS PROVIDED HIGH
CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY IS
ASSESSED WITH HIGH CONFIDENCE DUE TO THE ALIGNMENT OF THE BULK OF
THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES NOTED ABOVE. THE
ENVIRONMENT CONTINUES TO BE FAVORABLE FOR ADDITIONAL
INTENSIFICATION, AND THERE ARE SOME INITIAL SIGNALS OF A POSSIBILITY
OF RAPID INTENSIFICATION (RI).

INITIAL WIND RADII BASIS: SAR AND SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   DEMS: T4.5 - 77 KTS
   APRF: T4.0 - 65 KTS
   CIMSS SATCON: 69 KTS AT 270510Z
   CIMSS ADT: 79 KTS AT 270540Z
   CIMSS AIDT: 78 KTS AT 270540Z
   CIMSS D-PRINT: 54 KTS AT 270630Z

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

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: TC 27S IS FORECAST TO CONTINUE TRACKING
WESTWARD FOR THE NEXT 12 TO 24 HOURS, ALONG THE NORTHERN SIDE OF A
STR CURRENTLY CENTERED TO THE SOUTH AND SOUTHWEST OF THE TC. THE
STR QUICKLY SLIDES EASTWARD AND WILL BE POSITIONED TO THE SOUTHEAST
OF TC 27S BY TAU 36, ALLOWING THE SYSTEM TO SLOWLY ARC ONTO A MORE
SOUTHWESTWARD TRACK THROUGH TAU 72. THE APPROACH OF A DEEP
UPPER-LEVEL TROUGH FROM THE WEST, WILL ERODE AND PUSH THE STR TO
THE EAST, ALLOWING TC 27S TO ROUND THE RIDGE AXIS AND TURN
SOUTHWARD AFTER TAU 72. ANOTHER RIDGE QUICKLY MOVES IN FROM THE
WEST AFTER PASSAGE OF THE TROUGH, AND TC 27S WILL SLOW DOWN
DRAMATICALLY BY THE END OF THE FORECAST PERIOD AS IT RUNS INTO THE
STRONG RIDGING TO THE SOUTH. IN TERMS OF INTENSITY, AS OUTLINED
ABOVE, THERE ARE SIGNALS EMERGING IN THE WATER VAPOR IMAGERY OF THE
ENVIRONMENT SETTING UP FOR A PERIOD OF FURTHER INTENSIFICATION IN
THE NEAR TERM. THIS IS BORNE OUT BY THE HAFS-A MODEL WHICH SHOWS
ONSET OF RI BY TAU 12, QUICKLY REACHING A PEAK OF 115 KNOTS. THE
REMAINDER OF THE AVAILABLE GUIDANCE HOWEVER DOES NOT SUPPORT RI BUT
DOES SHOW MODEST ADDITIONAL INTENSIFICATION. THERE IS PLENTY OF
AVAILABLE MOISTURE AND SSTS REMAIN MODERATELY WARM. AROUND TAU 48,
THE SYSTEM WILL ALSO BEGIN TO TAP INTO A STRONGER POLEWARD OUTFLOW
CHANNEL, WHICH SHOULD FUEL ADDITIONAL INTENSIFICATION THROUGH AT
LEAST THAT POINT AND POTENTIALLY AS LATE AS TAU 72. HOWEVER, BY TAU
72, DEEP-LAYER SHEAR IS FORECAST TO INCREASE SHARPLY AND DRY
MID-LEVEL AIR WILL BEGIN TO INTRUDE INTO THE CORE OF THE SYSTEM,
MARKING THE ONSET OF A STEADY WEAKENING TREND THROUGH THE REMAINDER
OF THE FORECAST. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN MODERATE
AGREEMENT THROUGH TAU 72. GFS THE GEFS MEAN TURN THE SYSTEM MORE
SHARPLY POLEWARD FROM THE BEGINNING OF THE FORECAST AND MARK THE
INSIDE OR EASTERN EDGE OF THE ENVELOPE. THE NAVGEM IS THE WESTERN
OUTLIER, TAKING THE SYSTEM ON A MORE GRADUAL TURN THROUGH THE
FORECAST PERIOD. CROSS-TRACK SPREAD BETWEEN THE OUTLIERS IS 220NM
AT TAU 72, THOUGH THE REMAINDER OF THE GUIDANCE IS TIGHTLY PACKED
(45NM SPREAD) AROUND THE CONSENSUS MEAN. BEYOND TAU 72, THE
GUIDANCE CONTINUES TO SPREAD OUT, WITH THE GFS-GEFS COMBINATION
OUTPACING ALL OF THE OTHER MEMBERS OF THE CONSENSUS AND TURNING THE
SYSTEM SOUTHEASTWARD BY TAU 120, SUCH THAT CROSS-TRACK SPREAD OPENS
UP TO 470NM BY TAU 120. THE GEFS AND ECENS ENSEMBLES SHOW A SIMILAR
SPREAD, WITH ROUGHLY EQUAL NUMBERS OF MEMBERS SHOWING A WEST, SOUTH
AND SOUTHEASTWARD TRACK THOUGH THE ENSEMBLE MEAN TRACKS IN BOTH THE
ENSEMBLES SHOW A TURN TO THE WEST NEAR TAU 120. THE JTWC TRACK
STICKS WITHIN THE TIGHTLY GROUPED PACK OF MODELS THROUGH TAU 72,
THEN MOST CLOSELY TRACKS THE ECMWF DETERMINISTIC TRACKER
THEREAFTER. INTENSITY GUIDANCE IS MIXED, WITH THE HAFS-A DEPICTING
RI TO A PEAK OF 115 KNOTS WHILE THE REMAINDER OF THE GUIDANCE SHOWS
A MAXIMUM INTENSITY OF 90 KNOTS OR LESS. THE JTWC FORECAST IS ABOUT
15 KNOTS LOWER THAN THE HAFS-A BUT ROUGHLY 10 KNOTS HIGHER THAN THE
SHIPS GUIDANCE AND THE CONSENSUS MEAN. CONFIDENCE IS LOW, AND THE
POSSIBILITY OF RI CANNOT BE DISCOUNTED, WHICH COULD LEAD TO
SIGNIFICANTLY HIGHER INTENSITY IN THE NEAR-TERM. 

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