WDXS31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING NR 
017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.1S 71.9E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 125 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
DETERIORATING SYSTEM, WITH ONLY VERY WEAK, DISORGANIZED CONVECTION
NEAR THE ASSESSED CENTER POSITION. LOW TO MID-LEVEL SPIRAL BANDS
REMAIN WELL ORGANIZED IN ALL-QUADRANTS AND ARE CONTINUING TO WRAP
INTO AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). A 150455Z
AMSU-B 89GHZ MICROWAVE IMAGE SHOWED THE WELL-DEFINED LOW-LEVEL
BANDING FEATURES TO GOOD EFFECT, AS WELL AS A DEFINED LOW
EMISSIVITY REGION (LER) MARKING THE CENTER WITH HIGH CONFIDENCE. A
WELL-TIMED 180459Z ASCAT-B BULLSEYE PASS PROVIDED ADDITIONAL
CONFIDENCE TO THE INITIAL POSITION, PLACED JUST TO THE NORTHEAST OF
THE PREPONDERANCE OF AGENCY FIX POSITIONS. THE INITIAL INTENSITY
LIKEWISE IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE BULK OF
AGENCY DVORAK CURRENT INTENSITY ESTIMATES BETWEEN T3.0-T3.5 (45-55
KTS), THE SATCON AND ADT ESTIMATES AND SUPPORTED BY THE ASCAT PASS
WHICH SHOWED MAXIMUM WINDS IN THE 45-50 KNOT RANGE. ANALYSIS
REVEALS A MARGINAL ENVIRONMENT, CHARACTERIZED BY LOW (10-15 KTS)
WESTERLY VWS, WARM (28-29C) SSTS AND GOOD EASTWARD OUTFLOW, OFFSET
BY AN INFLUX OF DRY AIR ALONG THE WESTERN PERIPHERY OF THE SYSTEM.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN, BETWEEN A
DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE WEST AND A NEAR
EQUATORIAL RIDGE (NER) TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 52 KTS AT 180409Z
   CIMSS ADT: 45 KTS AT 180600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: WEAK EASTWARD OUTFLOW; MID-LEVEL DRY AIR
ENTRAINMENT FROM THE WEST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TC 19S (FABIEN) IS FORECAST TO CONTINUE
DRIFTING GENERALLY SOUTHWESTWARD FOR THE NEXT 24 TO 36 HOURS,
ENCASED IN THE COCOON BETWEEN THE TWO COMPETING RIDGES NOTED ABOVE.
THE OVERALL PATTERN IS EXPECTED TO SHIFT SOUTHWESTWARD, MOVING TC
19S ALONG WITHIN IT. AS THE SYSTEM DRIFTS SLOWLY SOUTHWESTWARD,
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN RELATIVELY STEADY,
AND THUS NO SIGNIFICANT CHANGES IN THE INTENSITY ARE EXPECTED,
THOUGH SHORT-TERM DEPARTURES ABOVE OR BELOW 45 KNOTS CAN BE
EXPECTED DUE TO DIURNAL EFFECTS. BY TAU 36, THE NER TO THE NORTH IS
EXPECTED TO WEAKEN AND RECEDE TO THE NORTH, AT THE SAME TIME AS AN
UPPER-LEVEL TROUGH PASSES TO THE SOUTH, ALLOWING FOR TC 19S TO
BREAK OUT OF ITS COCOON AND BEGIN TO TRACK POLEWARD. AS THE SYSTEM
MOVES TOWARDS THE SOUTH IT WILL MOVE INTO STEADILY COOLER WATERS,
LEADING TO A STEADY, ALBEIT RELATIVELY SLOW, WEAKENING TREND. AFTER
ABOUT TAU 96, WHEN THE SYSTEM IS EXPECTED TO WEAKEN TO A VERY WEAK
TROPICAL STORM, THE STEERING LEVEL WILL LOWER TO AROUND 700MB, AND
THE PRIMARY STEERING MECHANISM WILL TRANSITION TO THE LOW-LEVEL
ANTICYCLONE FAR TO THE SOUTH, PUSHING TC 19S ONTO A MORE WESTWARD
TRACK BY THE END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN POOR
AGREEMENT, NOT UNEXPECTED FOR A WEAK STEERING PATTERN. THE GALWEM
MODEL TRACKS THE SYSTEM IN A FULL CLOCKWISE LOOP FROM TAU 00, THE
NAVGEM, TURNS THE SYSTEM TO THE NORTH, THEN DOES A 180 TO THE
SOUTH, WHILE THE GFS AND GEFS ENSEMBLE MEAN TAKE THE SYSTEM MUCH
FURTHER EAST BEFORE EVENTUALLY TURNING SOUTHWEST BY TAU 120. THE
REMAINDER OF THE CONSENSUS ARE CLOSELY GROUPED AROUND THE PGTW
FORECAST RACK. THE GEFS AND ECENS ALSO SHOW A LARGE AMOUNT OF
SPREAD, INDICATIVE OF THE HIGHLY UNCERTAIN TRACK FORECAST. THE JTWC
FORECAST LIES CLOSE TO THE CONSENSUS MEAN (WITHOUT THE GALWEM AND
NAVGEM), WITH LOW CONFIDENCE. INTENSITY GUIDANCE IS IN MODERATELY
GOOD AGREEMENT, SHOWING GRADUAL WEAKENING THROUGH THE FORECAST
PERIOD, LENDING MEDIUM CONFIDENCE TO THE JTWC INTENSITY FORECAST. 

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