WDXS31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) 
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.8S 73.8E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 128 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE 21NM
EYE FEATURE WITH DEEP CONVECTIVE BANDS MOSTLY ISOLATED TO THE
EASTERN SEMICIRCLE OF THE SYSTEM. A 170428Z AMSU-B 89GHZ MICROWAVE
IMAGE FURTHER ILLUSTRATES THE EXTENT OF THE DRY AIR INTRUSION
WITHIN THE WESTERN QUADRANT OF THE SYSTEM. A SINGLE DEEP CONVECTIVE
BAND IS EVIDENT WRAPPING INTO THE LLCC FROM THE SOUTH. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON MSI AND AMSU-B
IMAGERY. THE INITIAL INTENSITY OF 95 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON A CONSENSUS AMONGST DVORAK CURRENT INTENSITY
ESTIMATES AND AUTOMATED INTENSITY ESTIMATES WHICH GENERALLY
INDICATE 90-102KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T5.0 - 90 KTS
   DEMS: T5.5 - 102 KTS
   FMEE: T4.5 - 77 KTS
   FIMP: T5.0 - 90 KTS
   CIMSS SATCON: 95 KTS AT 170302Z
   CIMSS ADT: 99 KTS AT 170600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: UPWELLING AND DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 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 STEADILY INCREASING
DRY AIR ENTRAINMENT. THIS COUPLED WITH UPWELLING OF COOLER WATERS
AS THE SYSTEM TRANSITS OVER SHALLOW OCEAN HEAT CONTENT (OHC)
REGIONS WILL CONSPIRE TO GRADUALLY WEAKEN THE SYSTEM. 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 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 MOSTLY HALTED AFTER WHICH A SHARP DIRECTIONAL
CHANGE IS FORECAST TO TAKE PLACE. FURTHERMORE, NEAR TAU 72,
VERTICAL WIND SHEAR (VWS) IS FORECAST TO SIGNIFICANTLY INCREASE
RESULTING IN AN INTENSITY NEAR 45KTS BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT THROUGH
TAU 72, WITH ALL MEMBERS GENERALLY FOLLOWING THE JTWC FORECAST
TRACK. BY TAU 72, THE SPREAD IN MODEL OUTPUT GREATLY INCREASES AS
VARIOUS 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 ALSO
IN FAIR AGREEMENT WITH A BULK OF THE GUIDANCE GENERALLY FOLLOWING
THE TREND OF THE JTWC FORECAST INTENSITY. 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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