WDXS31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) 
WARNING NR 024//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.0S 69.3E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 258 NM SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN ELONGATED
CIRCULATION WITH AN ASYMMETRIC CONVECTIVE COVER FULLY OBSCURING THE
LOW LEVEL CIRCULATION CENTER (LLCC) BENEATH.  A RECENT 200418Z
ASCAT-B SCATTEROMERTY PASS REVEALS A SIMILARLY ASYMMETRIC WIND
FIELD WITH 45-50 KNOT WINDS EXCLUSIVELY IN THE SOUTHWESTERN
QUADRANT WHILE 25-30KT WINDS DOMINATE THE NORTHERN SEMICIRCLE. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
SCATTEROMERTY DATA AND MSI IMAGERY. THE INITIAL INTENSITY OF 50KTS
IS ASSESSED WITH HIGH CONFIDENCE BASED PRIMARILY ON SCATTEROMETERY
DATA THOUGH THE PREPONDERANCE OF INTENSITY ESTIMATES BOTH DVORAK
AND CIMMS ALSO INDICATE 19S HAS MAINTAINED 50KTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE (STR) OVER NORTHERN MADAGASCAR AND A NEAR
EQUATORIAL RIDGE (NER) SOUTH OF SRI LANKA.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   FIMP: T3.5 - 55 KTS
   CIMSS SATCON: 46 KTS AT 200408Z
   CIMSS ADT: 47 KTS AT 200600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: HAVING RECENTLY REACHED ITS APOGEE, TC 19S
(FABIEN) IS FORECAST TO MAKE A POLEWARD SHIFT OVER THE NEXT 12
HOURS. DURING THIS TIME, AS VERTICAL WIND SHEAR (VWS) REMAINS LOW
AND OUTFLOW REMAINS GENERALLY FAVORABLE, THE SYSTEM IS FORECAST TO
MAINTAIN ITS INTENSITY. BY TAU 24, NOW TRACKING GENERALLY SOUTHWARD
IN A POOR STEERING ENVIRONMENT, VWS AND VERTICAL TILTING INCREASES
AND UPPER LEVEL OUTFLOW WEAKENS RESULTING IN GRADUAL WEAKENING. BY
TAU 72, A BUILDING STR JUST EAST OF THE SYSTEM FORCES FABIEN
WESTWARD UNTIL ITS EVENTUAL DISSIPATION BY 96.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH ALL
MEMBERS GENERALLY FOLLOWING THE JTWC FORECAST TREND THROUGH TAU 72.
AFTER TAU 72, AS THE NEW STR TO THE EAST EXERTS STEERING INFLUENCE,
AND MEMBER GUIDANCE FANS OUT CONSIDERABLY AS SOLUTIONS STRUGGLE TO
ACCOUNT FOR THIS NEW ELEMENT. FOR THIS REASON THE JTWC TRACK
FORECAST IS PLACED INITIALLY WITH MEDIUM CONFIDENCE AND EVENTUALLY
WITH LOW CONFIDENCE. RELIABLE MODEL INTENSITY GUIDANCE IS IN GOOD
AGREEMENT WITH A BULK OF THE MEMBERS STAGNATING THE SYSTEM THROUGH
TAU 12 AFTER WHICH ALL MEMBERS WEAKEN THE SYSTEM THROUGH THE
FORECAST PERIOD. FOR THIS REASON THE JTWC FORECAST INTENSITY IS
PLACED WITH OVERALL MEDIUM CONFIDENCE.

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