WDXS31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.4S 71.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 153 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 EXPOSED
LOW-LEVEL SPIRAL BANDS ALONG THE ENTIRE WESTERN PERIPHERY OF THE
SYSTEM, WRAPPING INTO A LOW LEVEL CIRCULATION CENTER (LLCC) WHICH
IS OBSCURED BY A RECENT FLARE UP OF CONVECTION. THE LOW-LEVEL
STRUCTURE OF THE EASTERN PORTION OF THE SYSTEM REMAINS OBSCURED BY
CONVECTIVE DEBRIS MOVING DOWNSTREAM ALONG THE OUTFLOW VECTOR. A
181124Z SSMIS 91GHZ MICROWAVE IMAGE REVEALED SHALLOW CONVECTIVE
BANDS WRAPPING INTO THE LLCC WITH A BAND OF CYCLONICALLY CURVED
CONVECTION ORIGINATING NEAR THE CENTER AND EXTENDING SOUTHEASTWARD.
ANALYSIS OF THE 91GHZ AND 37GHZ IMAGES SUGGESTS THE VORTEX IS
TILTED TO THE SOUTHEAST WITH HEIGHT, CONSISTENT WITH THE MODERATE
WEST-NORTHWESTERLY SHEAR. THE INITIAL POSITION IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED MICROWAVE IMAGE. THE
INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
BULK OF THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES AND THE
SATCON. THE ENVIRONMENT IS OVERALL MARGINAL, WITH MODERATE VWS,
WARM SSTS AND MODEST EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN CHARACTERIZED BY
A 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: T3.0 - 45 KTS
   FMEE: T3.0 - 45 KTS
   CIMSS SATCON: 45 KTS AT 180900Z
   CIMSS ADT: 39 KTS AT 181200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT IN THE WESTERN PERIPHERY.

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: THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE
FORECAST FOR TC 19S (FABIEN). THE SYSTEM IS STILL EXPECTED TO TRACK
SLOWLY SOUTHWESTWARD THROUGH TAU 36, AS THE COCOON IT IS NESTLED
IN, BETWEEN THE NER TO THE NORTHEAST AND THE STR TO THE SOUTHWEST,
ITSELF DRIFTS TOWARDS THE SOUTHWEST. AFTER TAU 36, TWO CHANGES
OCCUR SIMULTANEOUSLY; THE NER STRENGTHENS AND BEGINS TO MOVE TO THE
WEST, WHILE THE STR REMAINS OVER NORTHERN MADAGASCAR, AND A
UPPER-LEVEL TROUGH WILL SLIDE BY TO THE SOUTH OF THE SYSTEM. THE
COMBINATION OF THESE CHANGES WILL EJECT TC 19S TOWARDS THE
SOUTHEAST. AS THE OVERALL ENVIRONMENT IS MARGINAL AND IS NOT
EXPECTED TO CHANGE, THERE IS NO MAJOR CHANGE FORECAST IN THE
INTENSITY THROUGH TAU 36, THOUGH SHORT-DURATION EXCURSIONS ABOVE OR
BELOW THE FORECAST INTENSITY ARE POSSIBLE DUE TO DIURNAL EFFECTS OR
SHORT-TERM MESOSCALE CHANGES IN THE ENVIRONMENT. HOWEVER, AFTER TAU
36 AS THE SYSTEM STARTS TO MOVE TO THE SOUTHEAST, GLOBAL MODELS
SUGGEST WAVES OF SOUTHWESTERLY FLOW WILL MOVE OVER THE SYSTEM,
USHERING IN PULSES OF DRY MID-LEVEL AIR AND INCREASES IN SHEAR,
STEADILY WEAKENING THE SYSTEM DOWN TO JUST 35 KNOTS BY TAU 96. AS
THE SYSTEM WEAKENS TO A WEAK TROPICAL STORM THE STEERING LEVEL WILL
LOWER TO THE 850-700MB LAYER. THE LOW-LEVEL ANTICYCLONE TO THE
SOUTH WILL THEN ASSUME THE PRIMARY STEERING ROLE, AND TC 19S WILL
SHIFT TO A WESTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST
PERIOD. 

MODEL DISCUSSION: WHILE THE MAJORITY OF THE GUIDANCE AGREES ON THE
OVERALL S-TYPE TRACK SCENARIO, THE TIMING AND STRENGTH OF THE TURNS
IS HIGHLY UNCERTAIN. OVERALL SPREAD IN THE GUIDANCE INCREASES TO
JUST UNDER 300NM BY TAU 120 WITH THE NAVGEM ON THE WEST AND EGRR ON
THE EAST SIDE OF THE ENVELOPE. THE JTWC FORECAST HEDGES TOWARDS THE
GFS SOLUTION THROUGH THE MAJORITY OF THE FORECAST, THOUGH
CONFIDENCE REMAINS LOW THROUGHOUT THE FORECAST PERIOD. INTENSITY
GUIDANCE IS MIXED, WITH THE HWRF AND COAMPS-TC SUGGESTING SLIGHT
(5-10 KTS) INTENSIFICATION THROUGH TAU 24 FOLLOWED BY SHARP
WEAKENING, WHILE THE DECAY-SHIPS (BOTH GFS AND NAVGEM) SHOW SHARP
WEAKENING THROUGH TAU 36 FOLLOWED BY A LEVELING OFF THROUGH THE
REMAINDER OF THE FORECAST. THE JTWC FORECAST MOST CLOSELY TRACKS
THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE. 

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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