WDXS31 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08S (BATSIRAI) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6S 76.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 721 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS RAGGED DEEP
CONVECTION OVER A COMPACT LOW LEVEL CIRCULATION CENTER, REFLECTING
THE RAPID WEAKENING THAT HAS OCCURRED OVER THE PAST TWELVE HOURS
FOLLOWING A VERY SHORT-LIVED PERIOD OF EXPLOSIVE DEEPENING. A
012723Z SSMIS PASS REVEALS DEEP CONVECTION IS DISPLACED TO THE
SOUTHERN SEMI-CIRCLE DUE TO NORTHERLY VERTICAL WIND SHEAR. THE
INITIAL POSITION WAS PLACED WITH GOOD CONFIDENCE BASED ON FIXES
FROM PGTW AND FMEE, AND SUPPORTED BY THE SSMIS. THE INTENSITY
WAS LOWERED TO 50 KNOTS, WITH BOTH AGENCIES HAVING A FINAL T-NUMBER
OF 3.0, AND WITH CIS RANGING FROM 4.0 TO 5.0. THE LATEST CIMSS
SATCON INDICATES 46 KNOTS, ALTHOUGH ADT HAS BEEN LOW-BIASED
THROUGHOUT THE LAST DAY. SOME CONSIDERATION IS GIVEN TO THE SMALL
SIZE OF THE SYSTEM. BATSORAI IS UNDER MODERATE 15 TO 20 KNOT SHEAR
IN THE GFS, WHICH IS CONSISTENT WITH THE SSMIS IMAGERY. SST
ANALYSIS INDICATES TC 08S IS TRACKING OVER A TONGUE OF SLIGHTLY
COOLER (28 DEGREE CELSIUS) WATERS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: TC 08S IS EMBEDDED ALONG THE SOUTHERN
PERIPHERY OF A BROADER MONSOONAL GYRE TYPE PATTERN, ENFORCED BY THE
STRONG MASCARENE HIGH TO THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   CIMSS SATCON: 52 KTS AT 272032Z
   CIMSS ADT: 43 KTS AT 280015Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: THE INTERACTION WITH THE MONSOON GYRE IS
COMPLICATING THE MOTION, AND THE COMPACT NATURE OF TC 08S IS
CHALLENGING TO ASSESS CURRENT INTENSITY ACCURATELY. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FIRST 24 HOURS OF THE FORECAST
INTENSITY WAS LOWERED TO ACCOUNT FOR THE RAPID WEAKENING THAT 
OCCURRED.

FORECAST DISCUSSION: TC BATSIRAI IS EXPECTED TO TRACK GENERALLY
SOUTH-SOUTHWESTERLY TO WESTERLY OVER THE NEXT 48 HOURS WITHIN THE
BROADER MONSOONAL GYRE FLOW, WHICH IS MODULATED BY THE STRONG DEEP-
LAYER SUBTROPICAL RIDGE TO THE SOUTH. MID-LEVEL DRYING AND PERSISTENT
SHEAR IS FORECAST TO HAMPER REDEVELOPMENT DURING THIS PERIOD.
HOWEVER, AFTER TAU 48 THE TRACK IS EXPECTED TO DEFLECT EQUATORWARD,
ACCOMPANIED BY INCREASED MOISTENING AND A RELAXATION OF THE SHEAR. 
A WEAKNESS IN THE RIDGE SHOULD THEN ALLOW ANOTHER TURN TO THE
SOUTH-SOUTHWEST AT THE END OF THE FORECAST. THE SMALL SIZE OF THE
CURRENT CORE, COMBINED WITH THE BROADER INTERACTION WITH THE GYRE
FLOW AND THE POOR GUIDANCE RELIABILITY THUS FAR MAKE THE INTENSITY
FORECAST CHALLENGING. THE FORECAST IS SLIGHTLY HIGHER THAN THE
CURRENT GUIDANCE ENVELOP GIVEN THE POTENTIAL TO RAPIDLY ADJUST TO
ANY POSITIVE ENVIRONMENTAL CHANGES, ALTHOUGH THE FORECAST CALLS FOR
THE SHEAR AND DRY ENVIRONMENT TO LIMIT INTENSIFICATION THROUGH TAU
48. A SECONDARY PEAK OF 70 KNOTS IS ANTICIPATED AROUND TAU 96 AS
CONDITIONS IMPROVE. FORECAST CONFIDENCE IS GENERALLY LOW GIVEN THE
LARGE SPREAD IN MODEL GUIDANCE AND INTENSITY CHALLENGES DESCRIBED
BELOW.

MODEL DISCUSSION: MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT
THROUGH TAU 48, AND THEN DIVERGES SIGNIFICANTLY. NAVGEM AND UKMET
MODELS TAKE TC 08S ON A SOUTHWESTERLY TRACK, INTO THE RIDGE TO THE
SOUTH. GFS AND GFS ENSEMBLE ARE NEAR THE TOP OF THE OTHER GROUPING 
WITH A WESTERLY TRACK, AND ARE ALSO THE FASTEST AIDS. THE ECMWF 
DETERMINISTIC IS CLOSER TO THE GFS, ALBEIT SLOWER, WHILE THE EC 
ENSEMBLE HAS A FAIR NUMBER OF MEMBERS THAT SUGGEST A MORE 
SOUTHWESTERLY TRACK IS POSSIBLE BEYOND TAU 48. THE FORECAST WAS 
PLACED BETWEEN THE GFS AND ECMWF DETERMINISTIC SOLUTIONS. INTENSITY 
GUIDANCE IS MIXED THROUGH TAU 48, BUT GENERALLY AGREES WITH THE 
EXPECTED RE-INTENSIFICATION AFTER TAU 48.

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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