WDXS31 PGTW 202100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING NR 
025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.2S 69.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 270 NM SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
QUICKLY DETERIORATING AND ELONGATING THE ASYMMETRIC SYSTEM WITH
MOST OF THE CONVECTION WASHING AWAY OVERNIGHT. THE LOW-LEVEL
CIRCULATION CENTER (LLCC) IS PARTIALLY EXPOSED DUE TO THE DENSE
CIRRUS. A COARSE 201649Z METOP-B AMSU-B 89GHZ IMAGE REVEALS VERY
LIMITED CONVECTION REMAINING ON THE WESTERN SIDE OF THE DECAYING
SYSTEM. THE INITIAL POSITION AND INTENSITY ARE ASSESSED WITH MEDIUM
CONFIDENCE BASED UPON MULTIPLE DVORAK AGENCY FIX POSITIONS AND
OBJECTIVE DVORAK INTENSITY ESTIMATES AS THERE WAS A LACK OF IN-SITU
DATA IN THE REGION. THE SYSTEM APPEARS TO BE DECAYING A BIT MORE
RAPIDLY THAN PREVIOUSLY FORECASTED WITH WEAK POLEWARD OUTFLOW, LOW
TO MODERATE 10-15 KNOTS VERTICAL WIND SHEAR (VWS), AND WARM
(27-28C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: PERSISTENCE 

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: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS ADT: 53 KTS AT 201800Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 19S (FABIEN) WILL CONTINUE ON A POLEWARD
JOURNEY OVER THE NEXT 12 HOURS. DURING THIS TIME, THE VERTICAL WIND
SHEAR (VWS) WILL REMAIN RELATIVELY LOW, AND THE OUTFLOW GENERALLY
FAVORABLE. THE SYSTEM WILL MAINTAIN ITS CURRENT INTENSITY AS IT
TRACKS SOUTH IN THE WEAK STEERING ENVIRONMENT. THE SYSTEM WILL
BECOME MORE ASYMMETRIC AS THE UPPER-LEVEL CIRCULATION TILTS AND
DECOUPLES FROM THE LLCC BY TAU 24.  THE RESULTING EFFECT WILL BE A
LLCC MOVING WEST DISSIPATING OVER THE OPEN OCEAN BY TAU 72, IF NOT
SOONER.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT WITH MOST
MEMBERS GENERALLY FOLLOWING THE JTWC FORECAST TREND THROUGH TAU 72.
HOWEVER, THE CROSS-TRACK SPREAD INCREASES FROM 92NM IN THE FIRST 24
HOURS TO OVER 310NM BY TAU 72, LENDING OVERALL LOW CONFIDENCE IN
THE OVERALL JTWC TRACK. RELIABLE MODEL INTENSITY GUIDANCE IS IN
GOOD AGREEMENT AS THE SYSTEM MAINTAINS A 35-KNOT SYSTEM DRIFTING TO
THE SOUTH UNDER THE WEAK STEERING FLOW, FOR THIS REASON, THE JTWC
FORECAST INTENSITY IS ASSESSED WITH OVERALL MEDIUM CONFIDENCE.

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