WDXS31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 27S (TWENTYSEVEN) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 108.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 461 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE 27S WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND DEEP CONVECTIVE BURSTS ALONG THE WESTERN SECTOR OF THE
LLCC. MODERATE NORTHEASTERLY VERTICAL WIND SHEAR CONTINUES TO ACT
ON THE SYSTEM, CAUSING THE VORTEX TO TILT WESTWARD WITH HEIGHT. A 
251116Z F17 SSMIS 91 GHZ MICROWAVE IMAGE SHOWS A VERY STRONG BURST OF 
CONVECTION NEAR THE CENTER WITH THE EXPOSED LOW-LEVEL CLOUD LINES 
WITHIN THE EASTERN SEMICIRCLE. ENVIRONMENTAL ANALYSIS INDICATES THAT 
27S IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE 
POLEWARD AND EQUATORWARD OUTFLOW, MODERATE (15-20 KTS) VERTICAL WIND 
SHEAR, AND WARM (28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL 
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTIALLY 
EXPOSED LLCC IN THE ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 40 
KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGHER END OF THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   APRF: T2.5 - 35 KTS
   CIMSS SATCON: 46 KTS AT 251210Z
   CIMSS ADT: 37 KTS AT 251210Z
   CIMSS AIDT: 34 KTS AT 251210Z
   CIMSS DPRINT: 36 KTS AT 251210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

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, ALONG THE NORTHERN PERIPHERY OF THE STR, THROUGH TAU 36.
NEAR TAU 36, A LONGWAVE TROUGH IS EXPECTED TO BREAK DOWN THE STR,
BUT A SECOND STR WILL FOLLOW AND BUILD TO THE SOUTH OF THE SYSTEM.
THIS WILL ALLOW 27S TO TRACK FURTHER WESTWARD RATHER THAN BEGINNING
A POLEWARD TURN. THE SYSTEM WILL THEN EVENTUALLY ROUND THE
NORTHWESTERN PERIPHERY OF THE SECOND STR NEAR TAU 120. REGARDING
INTENSITY, TC 27S IS FORECAST TO SLIGHTLY INTENSIFY OVER THE NEXT
24 HOURS DUE TO THE SHEAR DROPPING TO AROUND 10-15 KTS.
THE SYSTEM WILL THEN MAINTAIN INTENSITY THROUGH TAU 48. NEAR TAU
48, SHEAR IS EXPECTED TO DROP FURTHER, BELOW 10 KTS, ALLOWING FOR
THE SYSTEM TO INTENSIFY TO AROUND 65 KTS AT TAU 96. AFTER TAU 96,
DRY AIR AND COOLING SEA SURFACE TEMPERATURES ARE FORECAST TO HALT
FURTHER INTENSIFICATION AS THE SYSTEM BEGINS TO TRACK MORE
POLEWARD. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN MODERATE AGREEMENT
REGARDING THE TRACK OF 27S. CROSS-TRACK SPREAD REMAINS SMALL, BUT
ALONG-TRACK SPREAD CONTINUES TO BE AROUND 230 NM AT TAU 72 AND
PERSISTS THROUGHOUT THE FORECAST PERIOD. ECMWF IS THE FASTEST MODEL
WHILE GFS IS THE SLOWEST IN TERMS OF THE TRACK SPEED OF 27S. THE
JTWC TRACK FORECAST IS PLACED WITH OVERALL MEDIUM CONFIDENCE AS A
RESULT. INTENSITY GUIDANCE DISAGREES, PARTICULARLY AFTER TAU 60,
WITH A 75 KNOT SPREAD AT TAU 96. COAMPS-TC AND GFS ARE THE LEAST
AGGRESSIVE, SUGGESTING NO FURTHER INTENSIFICATION AFTER TAU 60. ON
THE OTHER HAND, HAFS-A IS THE MOST AGGRESSIVE, AND PEAKS AT 110 KTS
AT TAU 96. NOTABLY, THE GFS ENSEMBLE HAS NO MEMBERS THAT REACH 60
KTS WHILE THE ECMWF ENSEMBLE HAS A MAJORITY OF MEMBERS THAT REACH
60 KTS, FURTHER DISPLAYING THE DISAGREEMENT IN HOW MODELS DEVELOP
THE SYSTEM. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGH TAU 48 AND SLIGHTLY HIGHER
THEREAFTER, WITHOUT BITING OFF ON THE RAPID DEVELOPMENT THAT HAFS-A
SHOWS DUE TO THE EXPECTED DRY AIR AND LACK OF A STRONG OUTFLOW
CHANNEL.

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