WDXS31 PGTW 190900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.9S 70.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 224 NM SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RATHER
DISORGANIZED STRUCTURE, WITH FLARING DEEP CONVECTION FORMING A
RAGGED CENTRAL DENSE OVERCAST (CDO) FEATURE. CONVECTIVE ACTIVITY
LOOKS TO HAVE PEAKED AROUND THE 190000Z HOUR AND HAS STARTED TO
DISSIPATE, WITH WARMING CLOUD TOPS. WITH THE EXCEPTION OF A
LOW-RESOLUTION 190435Z AMSU-B 89GHZ IMAGE, THERE HAVE NOT BEEN ANY
GOOD QUALITY MICROWAVE PASSES AND THE RECENT SCATTEROMETER PASSES
MISSED THE CORE OF THE SYSTEM. THUS, THE INITIAL POSITION IS
ASSESSED WITH LOW CONFIDENCE, USING THE AGENCY FIX POSITIONS, WHICH
ARE THEMSELVES WIDELY DISPERSED ACROSS THE CDO. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, ON THE HIGHER END OF
THE SUBJECTIVE DVORAK CURRENT INTENSITY ESTIMATES, BUT SLIGHTLY
LOWER THAN THE ADT WHICH IS BEING PULLED A BIT TOO HIGH BASED ON
THE RECENT FLARE UP IN THE CONVECTIVE ACTIVITY. THE SYSTEM
CONTINUES TO DRIFT SLOWLY TOWARDS THE SOUTHWEST IN A WEAK STEERING
PATTERN. ANALYSIS REVEALS MARGINAL CONDITIONS WITH MODERATE
SOUTHWESTERLY VWS, WARM SSTS, MODERATE POLEWARD AND EQUATORWARD
OUTFLOW AND CONVERGENT, RELATIVELY DRY AIR ALONG THE WESTERN AND
SOUTHWESTERN PERIPHERY.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN WITH A
SUBTROPICAL RIDGE (STR) TO THE SOUTHWEST AND NEAR EQUATORIAL RIDGE
(NER) TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS ADT: 51 KTS AT 190600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: CONVERGENT UPPER-LEVEL FLOW AND DRY AIR TO THE
SOUTH AND WEST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: TROPICAL CYCLONE 19S (FABIEN) CONTINUES TO
TRACK SLOWLY SOUTHWESTWARD IN A WEAK STEERING ENVIRONMENT, CAUGHT
BETWEEN A SUBTROPICAL RIDGE (STR) IN THE NORTHERN MOZAMBIQUE
CHANNEL AND A NEAR EQUATORIAL RIDGE (NER) CENTERED SOUTH OF SRI
LANKA. THE SYSTEM IS FORECAST TO CONTINUE TO TRACK SLOWLY TOWARDS
THE SOUTHWEST FOR THE NEXT 24 HOURS. AROUND TAU 36, THE NER IS
EXPECTED TO STRENGTHEN AND MOVE TO THE SOUTHWEST, AND BEGIN TO
DOMINATE THE STEERING, PUSHING TC 19S TO THE SOUTHEAST INTO A
WEAKNESS IN THE UPPER-LEVEL RIDGE. THROUGH TAU 36, THE SYSTEM IS
FORECAST TO REMAIN RELATIVELY STATIC IN TERMS OF INTENSITY, WITH
CONTINUED SHORT-TERM EXCURSIONS ABOVE OR BELOW THE MEAN OF 45
KNOTS, DUE TO DIURNAL PULSES OF CONVECTIVE ACTIVITY. BY TAU 36
HOWEVER AS THE SYSTEM BEGINS TO MOVE OUT TO THE SOUTH, AN INCREASE
IN SHEAR AND A DECREASE IN SSTS WILL RESULT IN A GRADUAL WEAKENING
TREND. BY TAU 96 AS THE SYSTEM WEAKENS TO 35 KNOTS, IT WILL COME
UNDER THE STEERING INFLUENCE OF THE LOW TO MID-LEVEL ANTICYCLONE TO
THE SOUTH, AND START MOVING WESTWARD THROUGH THE REMAINDER OF THE
FORECAST PERIOD. THE SYSTEM IS CURRENTLY FORECAST TO MAINTAIN 35
KNOT INTENSITY THROUGH TAU 120, THOUGH IT IS POSSIBLE THAT IT COULD
DISSIPATE BELOW WARNING CRITERIA PRIOR TO TAU 120. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN POOR
AGREEMENT, WITH LARGE DISAGREEMENTS IN HOW EACH MODEL IS HANDLING
BOTH THE CURRENT WEAK STEERING ENVIRONMENT AND THE RATE OF
WEAKENING AND THUS THE ULTIMATE TIMING OF THE TURN TOWARDS THE
WEST. THE NAVGEM CONTINUES TO TRACK THE SYSTEM DUE WEST FROM THE
START OF THE FORECAST, WHILE THE GALWEM TAKES THE SYSTEM ON A BROAD
CLOCKWISE LOOP. MEANWHILE THE ECMWF AND ECENS ENSEMBLE MEAN TRACK
THE SYSTEM ON A FLATTER S-TYPE TRACK, NEARLY DUE SOUTH AFTER TAU
36. THE REMAINDER OF THE CONSENSUS MEMBERS SHOW A MORE SHARPLY
S-SHAPED TRACK. THE JTWC FORECAST HEDGES TOWARDS THE GFS SOLUTION,
ON THE EASTERN SIDE OF THE GUIDANCE ENVELOPE, WITH LOW CONFIDENCE.
INTENSITY GUIDANCE REMAINS RATHER MIXED, WITH THE HWRF AND
COAMPS-TC SUGGESTING SLIGHT INTENSIFICATION THROUGH TAU 24, AND THE
DECAY-SHIPS (NAVGEM) SUGGESTING STEADY INTENSIFICATION THROUGH THE
FORECAST PERIOD WHILE THE MESOSCALE MODELS SHOW STEADY WEAKENING TO
30 KNOTS BY TAU 72. THE JTWC FORECAST MOST CLOSELY TRACKS THE
CONSENSUS MEAN MEDIUM CONFIDENCE. 

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