WDXS31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 19S (FABIEN) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.2S 69.5E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 257 NM SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
PERSISTENT CONVECTIVE ACTIVITY NEAR THE ASSESSED LOW-LEVEL
CIRCULATION CENTER (LLCC). THE OVERALL STRUCTURE OF TC 19S (FABIEN)
REMAINS RELATIVELY DISORGANIZED AND IS ELONGATING. THE INITIAL
POSITION AND INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE USING A
PARTIAL 191713Z ASCAT METOP-B IMAGE. THE INTENSITY IS BASED BETWEEN
MULTIPLE DVORAK AGENCY INTENSITY ESTIMATES AND OBJECTIVE DVORAK
ESTIMATES AS LISTED. THE SYSTEM CONTINUES TO MOVE SLOWLY TO THE
SOUTHWEST IN THE WEAK STEERING PATTERN. WIND SHEAR HAS SLACKENED
SLIGHTLY, AND THE ENVIRONMENT REMAINS RELATIVELY FAVORABLE, WITH
WARM SSTS AND MODERATE POLEWARD AND EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA FROM A 191713Z METOP-B
ASCAT IMAGE.

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT WITH A
SUBTROPICAL RIDGE (STR) OVER NORTHERN MADAGASCAR AND A NEAR
EQUATORIAL RIDGE (NER) SOUTH OF SRI LANKA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS ADT: 55 KTS AT 191800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: THE SYSTEM WILL CONTINUE TRACKING SLOWLY TO
THE SOUTHWEST FOR THE NEXT 12 HOURS BEFORE TURNING POLEWARD AS THE
NER TO THE NORTHEAST STRENGTHENS AND MOVES WEST, BECOMING THE
DOMINANT STEERING INFLUENCE. A BRIEF PERIOD OF INTENSIFICATION TO
50 KNOTS IS STILL EXPECTED TO OCCUR IN THE NEXT 12 HOURS ONCE THE
SYSTEM ROUNDS THE AXIS, WIND SHEAR RELAXES, AND THE POLEWARD
OUTFLOW ENHANCES. SHORTLY AFTER THE TURN, THE SYSTEM WILL ONCE
AGAIN MAKE ANOTHER TURN TO THE SOUTHWEST AS THE COMPETING STEERING
MECHANISMS HAPPEN AGAIN AND INCREASE THE WIND SHEAR AND VERTICAL
TILT TO THE SYSTEM. THE COMBINATION EFFECTS OF COOLING OCEAN TEMPS
AND DECREASING OUTFLOW ALOFT WILL INHIBIT ANY FURTHER DEVELOPMENT
OF THE SYSTEM FOR THE REMAINDER OF THE FORECAST. THE SYSTEM IS
EXPECTED TO WEAKEN BELOW TROPICAL STORM STRENGTH NO LATER THAN TAU
96. AS THE SYSTEM STEADILY WEAKENS AND THE STEERING LEVEL LOWERS,
TC 19S WILL COME UNDER THE STEERING INFLUENCE OF THE LOW TO
MID-LEVEL ANTICYCLONE FAR TO THE SOUTH AND TURN ONTO A WESTWARD
TRACK AFTER TAU 72, ULTIMATELY LEADING TO THE DEMISE OF THE SYSTEM
BY TAU 96. 

MODEL DISCUSSION: TRACK GUIDANCE UNCERTAINTY CONTINUES TO REMAIN A
PROBLEM AS GUIDANCE HAS SPREAD TO 400NM BY TAU 96. THE CONSENSUS
MEMBERS AGREE ON THE S-SHAPED TRACK BUT DIVERGE AT TAU 72 AS THE
LOW TO MID-LEVEL STEERING BEGINS TO TAKE EFFECT. DUE TO THIS, THERE
IS ONLY MEDIUM CONFIDENCE WITH THE JTWC FORECAST TRACK, WHICH LIES
CLOSE TO THE GFS SOLUTION IN THE NEAR TAUS. TRACK CONFIDENCE WANES
AS THE SHIFTS TOWARDS THE SOUTHWEST OCCURS AT DIFFERENT INTERVALS
IN THE LATTER HALF, INCREASING THE UNCERTAINTY. A MAJORITY OF THE
INTENSITY GUIDANCE INDICATES 50 KTS THROUGH TAU 12, FOLLOWED BY
SLOW BUT STEADY WEAKENING THROUGH THE REMAINDER OF THE FORECAST
PERIOD WITH 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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