WDXS31 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09S (NINE) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.0S 66.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 502 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 09S (NINE) CONTINUES TO STRUGGLE TO
CONSOLIDATE A VERTICALLY ALIGNED VORTEX, AS DEPICTED IN ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI), WHICH SHOWS A COMPLETELY
EXPOSED AND DECOUPLED LOW LEVEL CIRCULATION CENTER (LLCC) DISPLACED
TO THE WEST OF REMNANT CONVECTIVE BLOWOFF. THE MOST RECENT MSI
HOWEVER, SHOWS A BLOSSOMING OF DEEP CONVECTION IN CLOSE PROXIMITY OF
THE LLCC, SUGGESTING THAT THE SYSTEM MAY FINALLY BE POISED TO
SYMMETRIZE. A 311147Z SSMIS 91GHZ IMAGE SHOWED THE LOW-LEVEL
BANDING FEATURES WRAPPING INTO THE WELL-DEFINED LLCC AND DEVELOPING
CONVECTION CONFINED TO A SMALL AREA JUST EAST OF THE LLCC. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
EXPOSED LLCC IN COMBINATION WITH THE MICROWAVE IMAGERY NOTED ABOVE.
THE INITIAL INTENSITY IS SET AT A GENEROUS 35 KNOTS BASED PRIMARILY
ON THE DVORAK CURRENT INTENSITY ESTIMATES OF 2.5 FROM MULTIPLE
AGENCIES, SUPPORTED BY THE CIMSS ADT ESTIMATE OF T2.3 (33 KNOTS)
AND AN AIDT ESTIMATE OF 40 KNOTS. THE ENVIRONMENT IS MARGINALLY
FAVORABLE WITH WARM SSTS, AND GOOD POLEWARD OUTFLOW, CONSTRAINED BY
DRY MID-LEVEL AIR TO THE WEST AND MODERATE MID-LEVEL WESTERLY SHEAR
AND CONVERGENT UPPER-LEVEL FLOW TO THE WEST. WHILE THE CIMSS SHEAR
ANALYSIS INDICATES JUST 10 KNOTS OF NORTHWESTERLY SHEAR, THE GFS
MODEL SOUNDINGS SUGGEST MID-LEVEL SHEAR UP TO 30 KNOTS WHICH
APPEARS GENERALLY TO BE SUPPORTED BY THE SATELLITE DEPICTION. THE
SYSTEM IS CURRENTLY IN A WEAK STEERING PATTERN, WITH NO CLEAR-CUT
STEERING MECHANISM AND IS THUS MEANDERING RATHER AIMLESSLY EAST OF
PORT MATHURIN.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS ADT: 33 KTS AT 311200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: STRONG MID-LEVEL SHEAR, CONVERGENT UPPER-LEVEL
FLOW AND DRY AIR TO THE WEST.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE WEAK STEERING PATTERN IS ANTICIPATED TO
REMAIN FIRMLY IN PLACE THROUGH THE NEXT 36 HOURS AND TC 09S WILL
CONTINUE TO MEANDER INSIDE THIS POCKET OF WEAK STEERING THROUGH AT
LEAST TAU 36. BY TAU 48, A MAJOR SHORTWAVE TROUGH WILL MOVE IN FROM
THE WEST AND COMBINE FORCES WITH A BUILDING STR TO THE NORTHEAST
AND EJECT TC 09S ONTO A SOUTHEASTWARD TRACK. AFTER TAU 48 AND
THROUGH THE REMAINDER OF THE FORECAST, TC 09S WILL ACCELERATE ALONG
THE TIGHT GRADIENT BETWEEN THE STR AND THE DEEPENING TROUGH,
REACHING TRACK SPEEDS APPROACHING 30 KNOTS BY THE END OF THE
FORECAST PERIOD. IN TERMS OF INTENSITY, EVERYTHING DEPENDS UPON THE
VORTEX AXISYMMETRIZATION PROCESS. THE LATEST SHIPS GUIDANCE
SUGGESTS A SLIGHT REDUCTION IN THE DEEP LAYER SHEAR, WHICH COULD
ALLOW FOR THE VORTEX TO ALIGN VERTICALLY AND THE CONVECTION TO
SUSTAIN ITSELF. HOWEVER, THIS WOULD BE OFFSET BY A LOCALIZED
REDUCTION IN SST DUE TO UPWELLING AS THE SYSTEM REMAINS
QUASI-STATIONARY. AROUND TAU 36, THE SHEAR IS EXPECTED TO REACH A
MINIMUM WHILE POLEWARD OUTFLOW BEGINS TO REALLY RAMP UP AS IT TAPS
INTO THE DIVERGENT FLOW AHEAD OF THE APPROACHING TROUGH, ALLOWING
FOR A BRIEF PERIOD OF INTENSIFICATION UP TO 40 KNOTS. BY TAU 72
SHEAR PICKS UP SHARPLY, TO AT LEAST 40 KNOTS AND COMES TO DOMINATE THE 
OUTFLOW AND THE SYSTEM WILL BE SHEARED APART. AT THIS POINT THE RACE 
WILL BE ON TO SEE WHICH HAPPENS FIRST, DISSIPATION OR EXTRATROPICAL 
TRANSITION (ETT). THE CURRENT FORECAST CALLS FOR BOTH TO OCCUR 
SIMULTANEOUSLY NO LATER THAN TAU 96, BUT THE SYSTEM COULD DISSIPATE 
WELL BEFORE THIS POINT, ESPECIALLY IF IT FAILS TO ORGANIZE IN THE 
NEAR-TERM. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS SOMEWHAT
SURPRISINGLY, GIVEN THE WEAK STEERING ENVIRONMENT, IN GOOD AGREEMENT
THROUGH TAU 72. ALL OF THE GUIDANCE SHOWS A TRACK NORTHWARD THROUGH
TAU 24, TURNING EAST THEN SOUTHEAST AFTER TAU 36. MODEL SPREAD
INCREASES TO 120NM AT TAU 72, THOUGH ALONG-TRACK SPREAD INCREASES
SHARPLY AFTER TAU 48 AS THE SYSTEM ACCELERATES POLEWARD. BY THE END
OF THE FORECAST, CROSS-TRACK SPREAD INCREASES TO A MODEST 170NM BUT
ALONG-TRACK SPREAD INCREASES TO OVER 700NM. THE UNCERTAINTY
ASSOCIATED WITH THE WEAK STEERING PATTERN, THE EXTREME ALONG-TRACK
SPREAD AFTER TAU 48 AND THE HIGH UNCERTAINTY IN WHETHER OR NOT THE
SYSTEM EVEN REACHES TAU 96, LENDS LOW CONFIDENCE TO THE JTWC
FORECAST TRACK. INTENSITY GUIDANCE IS MIXED, WITH ROUGHLY AN
EVEN SPLIT BETWEEN MODELS SHOWING DISSIPATION WITHIN THE NEXT 24
HOURS AND THOSE PEAKING THE SYSTEM NEAR 50 KNOTS BY TAU 72. THE
CONSENSUS MEAN ROUGHLY SPLITS THE DIFFERENCE AND THE JTWC FORECAST
HEDGES TO THE CONSENSUS WITH LOW CONFIDENCE. 

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