WDXS31 PGTW 010300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08S (BATSIRAI) 
WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.4S 62.3E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 361 NM NORTHEAST OF PORT LOUIS, MAURITIU
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT TC
08S CONTINUES TO STRUGGLE AGAINST PERSISTENT EASTERLY VERTICAL WIND
SHEAR (VWS). THE CONVECTION ASSOCIATED WITH TC 08S HAS STEADILY
WARMED OVER THE PAST TWELVE HOURS, BECOME INCREASINGLY DISORGANIZED
AND EXHIBITS A SHARP UPSHEAR EDGE, INDICATIVE OF THE PERSISTENT
SHEAR VECTOR. A 312052Z AMSR2 37GHZ MICROWAVE PASS SHOWED WELL
DEFINED BANDING FEATURES AND A WEAK MICROWAVE EYE WITH A WEAK OR
OPEN EYEWALL ON THE SOUTHERN SIDE. WHILE THE LOWER FREQUENCY
DEPICTED A WELL DEFINED EYE FEATURE, THE SAME CANNOT BE SAID FOR
THE UPPER 91GHZ FREQUENCY, WHICH SHOWED A COMPLETE LACK OF A
EYEWALL STRUCTURE ACROSS THE ENTIRE SOUTHERN HEMISPHERE OF THE
CIRCULATION. THE INITIAL POSITION IS ASSESSED WITH MEDIUM
CONFIDENCE, RELIANT PRIMARILY UPON EXTRAPOLATION OF THE MICROWAVE
EYE IN THE AMSR2 PASS. THE INITIAL INTENSITY REMAINS ASSESSED AT 75
KNOTS, BELOW THE PGTW T5.0 FIX INTENSITY, AND MORE IN LINE WITH THE
FMEE T4.5 ESTIMATE, BUT WELL ABOVE THE ADT ESTIMATE OF T3.6.
CONFIDENCE IS INCREASED IN LIGHT OF AN AMSR2 PASSIVE MICROWAVE
WINDSPEED ESTIMATE OF 70-77 KNOTS, WITH THE HIGHEST WINDS PRESENT
IN THE NORTHWESTERN QUADRANT. ANALYSIS REVEALS A MARGINALLY
FAVORABLE ENVIRONMENT, WITH MODERATE (20-25 KNOTS) EASTERLY SHEAR
BEING OFFSET BY MODERATE TO STRONG WEST AND POLEWARD OUTFLOW AND
WARM SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER
DATA 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE SOUTHWEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   FMEE: T4.5 - 77 KTS
   CIMSS ADT: 61 KTS AT 312115Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: MODERATE WESTWARD OUTFLOW

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: OVER THE PAST TWELVE HOURS, TC 08S HAS SLOWED,
REACHED A MAXIMUM EQUATORWARD POINT, AND THEN TURNED SOUTHWESTWARD,
AS THE STEERING MECHANISM HAS SWITCHED FROM A WEAK STEERING PATTERN
DOMINATED BY THE NEAR-EQUATORIAL RIDGE (NER) TO THE NORTH, TO ONE
DOMINATED BY THE STR TO THE SOUTHWEST. THROUGH THE FORECAST PERIOD,
THE STR IS EXPECTED TO SLOWLY DRIFT EASTWARD TO A POSITION DUE
SOUTH OF TC 08S BY TAU 72. AS THE RIDGE PASSES BY TO THE SOUTH, TC
08S WILL FIRST TRACK SOUTHWESTWARD TRACK THROUGH TAU 72, THEN TURN
TO A MORE WESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST
PERIOD. LANDFALL ALONG THE CENTRAL COAST OF MADAGASCAR IS EXPECTED
PRIOR TO TAU 120. IN THE NEAR-TERM, PERSISTENT MODERATE TO STRONG
EASTERLY SHEAR WILL LEAD TO A STEADY INTENSITY, OR SLIGHT WEAKENING
THROUGH TAU 24. AFTER TAU 36, THE SHEAR IS FORECAST TO BEGIN TO
SLACKEN, ALLOWING TC 08S TO REESTABLISH THE CONVECTIVE CORE, AND
EMBARK UPON A PERIOD OF STEADY INTENSIFICATION. AND MESOSCALE
UPPER-LEVEL ANTICYCLONE OR POINT SOURCE IS FORECAST TO DEVELOP OVER
TOP OF THE SYSTEM AROUND TAU 48, WHICH SHOULD ALLOW FOR A FASTER
RATE OF INTENSIFICATION TO PEAK OF 110 KNOTS BY TAU 96. IT IS
POSSIBLE THAT A SLIGHTLY HIGHER PEAK COULD BE REACHED BETWEEN TAU
96 AND LANDFALL, BUT SSTS ARE SLIGHTLY LOWER (27C) NEAR THE COAST,
WHICH COULD LIMIT THE PEAK INTENSITY POTENTIAL. ONCE THE SYSTEM
MAKES LANDFALL, IT WILL WEAK RAPIDLY AS IT INTERACTS WITH THE ROUGH
TERRAIN OF CENTRAL MADAGASCAR. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
72, WITH INCREASED UNCERTAINTY THEREAFTER. SPREAD BETWEEN OUTLIERS
IS APPROXIMATELY 100NM AT TAU 72, AND 300NM AT TAU 120, WITH NAVGEM
MARKING THE POLEWARD SIDE AND THE GFS ENSEMBLE MEAN THE EQUATORWARD
MARGIN OF THE GUIDANCE ENVELOPE. THE ALONG-TRACK SPREAD IS MINIMAL
THROUGH THE DURATION OF THE FORECAST. ENSEMBLE GUIDANCE SHOWS A
GOOD DEAL OF SPREAD, PARTICULARLY AFTER TAU 72, WITH MEMBERS
STRETCHING ACROSS EIGHT DEGREES OF LATITUDE ALONG THE COAST OF
MADAGASCAR. WHILE THE ENSEMBLE MEANS FOR BOTH ECMWF AND GFS ARE IN
CLOSE ALIGNMENT, THE LARGE SPREAD IN BOTH THE DETERMINISTIC AND
ENSEMBLE MEMBERS LENDS LOW CONFIDENCE TO THE JTWC TRACK AFTER TAU
72. INTENSITY GUIDANCE IS MIXED, WITH THE COAMPS-TC REACHING A PEAK
OF 125 KNOTS AT TAU 96, WHILE THE DECAY SHIPS SUGGESTS A PEAK AS
LOW AS 80 KNOTS AND THE HWRF PEAKING AT 90 KNOTS CLOSER TO TAU 72.
THE JTWC FORECAST TRACKS THE HWRF THROUGH TAU 36, THEN IS ABOVE ALL
BUT THE COAMPS-TC GUIDANCE THEREAFTER. CONFIDENCE IS LOW THROUGH
THE ENTIRE FORECAST. 

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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