WDXS31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) 
WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.9S 73.3E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 118 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
AS THE SUN ONCE AGAIN SETS ON TC 19S, ANIMATED MULTISPECTRAL
SATELLITE IMAGERY (MSI) DEPICTS AN ERODING CONVECTIVE COVER THAT IS
EXPOSING THE LLCC BELOW. WITH THE LAST FEW FRAMES OF DAYTIME
IMAGERY, THE LLCC AND UPPER LEVEL CIRCULATION CENTER (ULCC) ARE
BEGINNING TO DECOUPLE AS UPPER LEVEL WIND SHEAR INCREASES. A
171156Z GMI 89GHZ COLOR COMPOSITE MICROWAVE IMAGE SHOWS
SIGNIFICANTLY REDUCED CONVECTIVE ACTIVITY DUE TO DRY AIR INTRUSION
AS THE NORTHWESTERN QUADRANT OF THE CIRCULATION IS DEVOID OF ANY
DEEP CONVECTIVE STRUCTURES. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON MSI AND GMI IMAGERY. THE INITIAL
INTENSITY OF 90KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
DVORAK INTENSITY ESTIMATES AND AUTOMATED INTENSITY ESTIMATES
FALLING DUE TO SCENE TYPE CHANGE FROM THE LOSS OF THE EYE AND
OVERALL STRUCTURAL INTEGRITY BECOMING NOTICEABLY COMPROMISED. THE
BULK OF THE INTENSITY GUIDANCE REMAINS CLOSE TO THE JTWC INITIAL
INTENSITY OF 90KTS, FOR THIS REASON THE VALUE IS SET WITH OVERALL
MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: FADING INFLUENCE OF A SUBTROPICAL RIDGE
(STR) TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T5.0 - 90 KTS
   FMEE: T4.5 - 77 KTS
   FIMP: T5.0 - 90 KTS
   CIMSS SATCON: 85 KTS AT 170830Z
   CIMSS ADT: 94 KTS AT 170900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: UPWELLING AND DRY AIR ENTRAINMENT

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) IS FORECAST TO CONTINUE
TRACKING GENERALLY WEST-SOUTHWESTWARD UNDER THE FADING INFLUENCE OF
THE STR TO THE SOUTHEAST. AS EVIDENCED BY THE ERODING WESTERN
SECTOR OF THE SYSTEMS CONVECTIVE CORE, 19S IS EXPERIENCING
INCREASING DRY AIR ENTRAINMENT AND VERTICAL WIND SHEAR. THIS
COUPLED WITH UPWELLING OF COOLER WATERS AS THE SYSTEM TRANSITS OVER
SHALLOW OCEAN HEAT CONTENT (OHC) REGIONS WILL CONSPIRE TO WEAKEN
THE SYSTEM OVER THE NEXT 12-24 HOURS. BY TAU 24 AS THE ENVIRONMENT
SURROUNDING 19S CONTINUES TO DEGRADE, THE SYSTEM WILL TRANSITION
PRIMARY STEERING INFLUENCE TO A BUILDING STR OVER MADAGASCAR. AS A
RESULT, 19S WILL STEADY UP ON A GENERALLY WESTWARD TRACK AS THE
SYSTEM CONTINUES TO WEAKEN THROUGH TAU 48. BY TAU 72, 19S WILL
ENTER A COMPLEX AND COMPETING STEERING ENVIRONMENT AS THE STR TO
THE SOUTHWEST AND A BUILDING NEAR-EQUATORIAL RIDGE (NER) TO THE
NORTH COMPETE FOR STEERING CONTROL. AS A RESULT, THE SYSTEMS
FORWARD PROGRESS WILL BE HALTED AFTER WHICH A SHARP DIRECTIONAL
CHANGE IS FORECAST TO TAKE PLACE. FURTHERMORE, BY TAU 72, VERTICAL
WIND SHEAR (VWS) IS FORECAST TO SIGNIFICANTLY INCREASE RESULTING IN
AN INTENSITY NEAR 45KTS BY TAU 120.

MODEL DISCUSSION: NEAR-TERM MODEL GUIDANCE HAS CONTINUED TO IMPROVE
WITH A GENERALLY TIGHTER CROSS-TRACK AND ALONG-TRACK CONSENSUS
THROUGH TAU 72. AFTER TAU 72 HOWEVER, MODEL OUTPUT REMAINS IN POOR
AGREEMENT AS MEMBERS ATTEMPT TO RESOLVE THE COMPLEX STEERING
PATTERN DISCUSSED ABOVE. FOR THIS REASON THE JTWC FORECAST TRACK IS
PLACED WITH MEDIUM CONFIDENCE INITIALLY AND WITH LOW CONFIDENCE IN
THE EXTENDED TRACK FORECAST. RELIABLE MODEL INTENSITY GUIDANCE IS
IN FAIR AGREEMENT WITH A BULK OF THE GUIDANCE GENERALLY FOLLOWING
THE TREND OF THE JTWC FORECAST INTENSITY. HWRF AND COAMPS-TC
(NAVGEM VERSION) TAKE A MORE AGGRESSIVE WEAKENING TREND THROUGH THE
DURATION OF THE FORECAST PERIOD. FOR THIS REASON THE JTWC FORECAST
INTENSITY IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS 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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