WDXS31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08S (BATSIRAI) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.0S 79.6E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 1383 NM EAST OF ST DENIS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 25 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TC 08S HAS RAPIDLY INTENSIFIED (55 KNOTS) OVER THE PAST 12 HOURS,
INCREASING FROM 35 KNOTS AT 270000Z TO THE INITIAL INTENSITY OF 90
KNOTS AT 271200Z. THE SYSTEM IS CLASSIFIED AS A VERY SMALL SYSTEM
WITH A SMALL CENTRAL DENSE OVERCAST FEATURE. TC 08S DEVELOPED AN
EYE AT ABOUT 270900Z AND MAINTAINED A SMALL (7NM) ROUND EYE AT
271200Z, WHICH LED TO A MAJOR JUMP IN DVORAK ESTIMATES FROM
T2.5-3.0 (35-45 KNOTS) AT 270600Z TO THE CURRENT DVORAK ESTIMATES
RANGING FROM T5.0-T5.5 (90-102 KNOTS). THIS RAPID INCREASE IS
TYPICAL OF VERY SMALL SYSTEMS. CURRENTLY, ANIMATED ENHANCED
INFRARED SATELLITE IMAGERY DEPICTS A GRADUAL WEAKENING TREND AND
LOSS OF THE EYE FEATURE SINCE 271200Z. A 271311Z SSMIS 91GHZ IMAGE
INDICATES A SMALL CORE OF CENTRAL CONVECTION WITH SPIRAL BANDING
OVER THE SOUTHERN SEMICIRCLE. UPPER-LEVEL ANALYSIS INDICATES A VERY
FAVORABLE ENVIRONMENT WITH STRONG RADIAL OUTFLOW AND LOW VERTICAL
WIND SHEAR.

INITIAL WIND RADII BASIS: OTHER 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   FMEE: T5.5 - 102 KTS
   CIMSS ADT: 51 KTS AT 271215Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: DUE TO THE RAPID INTENSIFICATION
PHASE, THERE ARE MAJOR CHANGES IN THE JTWC INTENSITY FORECAST.

FORECAST DISCUSSION: TC 08S IS FORECAST TO TRACK WEST-SOUTHWESTWARD
THROUGH TAU 48 ALONG THE NORTHERN PERIPHERY OF THE STR. AFTER TAU
48, A MIDLATITUDE SHORTWAVE TROUGH WILL WEAKEN THE STR, WHICH WILL
LEAD TO A SLIGHT DECREASE IN FORWARD MOTION. TC 08S IS EXPECTED TO
WEAKEN STEADILY THROUGH TAU 36 BUT SHOULD REINTENSIFY AS POLEWARD
OUTFLOW IMPROVES FROM TAU 48 TO 72. AFTER TAU 72, TC 08S WILL TURN
WESTWARD TO WEST-NORTHWESTWARD AS IT TRANSITIONS TO THE STEERING
INFLUENCE OF A WESTERN STR BUILDING TO THE SOUTHWEST AFTER THE
MIDLATITUDE SHORTWAVE TROUGH PROPAGATES EASTWARD. UPPER-LEVEL
CONDITIONS ARE EXPECTED TO DEGRADE WITH INCREASING VERTICAL WIND
SHEAR (20 TO 25 KNOTS) AND WEAK DIFFLUENCE ALOFT THUS STEADY
WEAKENING IS ANTICIPATED. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH TAU 48 WITH A 83NM SPREAD IN SOLUTIONS AT TAU 48. AFTER TAU
48, THE NUMERICAL MODELS DIVERGE SIGNIFICANTLY WITH LARGE SPREAD
AND HIGH UNCERTAINTY. NAVGEM AND AFUM ARE OUTLIERS INDICATING A
SOUTHWARD TRACK, WHICH IS ASSESSED AS UNLIKELY, HOWEVER, THE
REMAINING GUIDANCE SHOWS SOLUTIONS TRACKING SOUTHEAST OF LA REUNION
TO NORTH OF LA REUNION. THE 270600Z ECMWF ENSEMBLE (EPS) ALSO
INDICATES A LARGE SPREAD IN ENSEMBLE SOLUTIONS. THERE IS A LARGE
DEGREE OF UNCERTAINTY IN THE JTWC INTENSITY FORECAST DUE TO THE
VERY SMALL SYSTEM SIZE AND POTENTIAL FOR RAPID INTENSITY CHANGES.  
 
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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