WDXS31 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 25S (KARIM) WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.3S 90.8E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 357 NM WEST OF THE COCOS ISLANDS,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED WATER VAPOR IMAGERY INDICATES IMPROVING POLEWARD OUTFLOW
INTO A SUBTROPICAL JET POSITIONED TO THE SOUTHWEST. THIS ROBUST
OUTFLOW CHANNEL IN COMBINATION WITH LOW VERTICAL WIND SHEAR (VWS)
AND WARM SST HAVE ALLOWED CORE CONVECTION TO PERSIST AND CONSOLIDATE
OVER THE LOW-LEVEL CIRCULATION CENTER (LLCC) AS EVIDENCED IN THE
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY. A 090353Z
METOP-B MHS 89GHZ MICROWAVE IMAGE REVEALS DEEP CONVECTIVE BANDING
OVER THE WESTERN SEMICIRCLE WRAPPING INTO THE NORTH AND NORTHEAST
QUADRANTS INDICATIVE OF THE IMPROVED ORGANIZATION. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THIS MHS IMAGE.
AFTER A SHORT-TERM DIP IN THE CIMSS ADT ESTIMATES, THE RECENT
ESTIMATES HAVE INCREASED BACK UP TO 59 KNOTS WITH AIDT ESTIMATES
ALSO INCREASING SLIGHTLY TO 58 KNOTS. CONSEQUENTLY, THE INITIAL
INTENSITY OF 60 KTS IS ASSESSED WITH HIGH CONFIDENCE, AND IS
HEDGED JUST ABOVE THE PGTW DVORAK ESTIMATE. 

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) POSITIONED
TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 090540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   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 25S IS FORECAST TO TRACK SOUTHWARD TO
SOUTH-SOUTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE NER THROUGH
TAU 24. DUE TO THE FAVORABLE ENVIRONMENTAL CONDITIONS, PARTICULARLY
THE ROBUST POLEWARD OUTFLOW CHANNEL, THE PEAK INTENSITY HAS BEEN
INCREASED TO 70 KNOTS AT TAU 24. AFTER TAU 24, THE SYSTEM WILL
TRACK WITHIN THE STEERING FLOW BETWEEN A BROAD UPPER-LEVEL TROUGH
AND A SUBTROPICAL RIDGE POSITIONED TO THE EAST. ENVIRONMENTAL
CONDITIONS SHOULD DEGRADE QUICKLY WITH INCREASING VERTICAL WIND
SHEAR OF 30-40 KNOTS AND INCREASING CONVERGENCE ALOFT ASSOCIATED
WITH THE AFOREMENTIONED UPPER-LEVEL TROUGH. THEREFORE, TC 25S WILL
WEAKEN STEADILY. NEAR TAU 48, A STRONG LOW-LEVEL HIGH WILL BUILD TO
THE SOUTH EFFECTIVELY HALTING POLEWARD TRACK MOTION AND COMMENCING
AN ABRUPT EQUATORWARD TRACK MOTION WITHIN THE LOW-LEVEL SOUTHEASTERLY
FLOW. INTERACTION WITH A WEAK BAROCLINIC ZONE, COOLER SST (25-26C) AND
SIGNIFICANT ENTRAINMENT OF DRY AIR WILL LEAD TO RAPID DISSIPATION AS
THE REMNANTS ACCELERATE NORTHWESTWARD.        

MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC GUIDANCE (EPS AND
GEFS) SUPPORT THE JTWC TRACK PHILOSOPHY WITH OVERALL MEDIUM
CONFIDENCE DUE TO DIFFERENCES IN THE TIMING AND EXACT TRACK DURING
THE STALL AND SHARP EQUATORWARD TRACK TURN. THE JTWC INTENSITY
FORECAST IS PLACED ABOVE THE JTWC INTENSITY CONSENSUS (ICNW), WHICH
PEAKS THE SYSTEM AT 62 KNOTS, AND IS LOWER THAN HWRF'S PEAK OF 85
KNOTS AT TAU 24. THERE IS CERTAINLY A POSSIBILITY THAT THE SYSTEM
COULD INTENSIFY MORE THAN EXPECTED WITHIN ITS SHORT WINDOW OF
OPPORTUNITY AS SUGGESTED IN THE COAMPS-TC (GFS INITIAL CONDITIONS)
ENSEMBLE, WHICH SHOWS A 20-30 PERCENT PROBABILITY FOR MODERATE
INTENSIFICATION (LESS THAN 30 KNOTS) WITHIN THE NEXT 24 HOURS.    

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