WDXS31 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (ELEVEN) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.0S 72.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 534 NM SOUTH OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS COOLING
TOPS ASSOCIATED WITH DEEPENING CONVECTION DOWNSTREAM OF THE LOW
LEVEL CIRCULATION CENTER (LLCC). THE CONVECTION IS SHEARED TO THE
EAST-SOUTHEAST OF THE LLCC LEAVING IT PARTLY EXPOSED, BUT A 292312Z
SSMIS CONFIRMS BOTH THE JTWC FIX AND THE VIGOR OF THE CONVECTION, 
PARTICULARLY OVER THE NORTHWEST QUADRANT. THE INITIAL INTENSITY 
ASSESSMENT IS HEDGED A LITTLE UPWARDS TO TROPICAL STORM STRENGTH 
BASED ON THE DEEPENING CONVECTION AND IS SUPPORTED BY AN ADT 
ASSESSMENT OF 33KTS.  THERE IS ALSO A BELT OF VIGOROUS EASTERLIES ON 
THE POLEWARD SIDE OF THE SYSTEM PROVIDING A BOOST TO LOW LEVEL 
VORTICITY. THE WINDFIELDS ARE ASYMMETRIC DUE TO THE VORTEX TRACKING 
AWAY FROM THE STRONGEST WESTERLIES IN THE MONSOON TROF AND TOWARDS 
THE BELT OF SEASONAL EASTERLIES OVER THE SOUTH CENTRAL INDIAN OCEAN. 
THE SYSTEM IS TRACKING THROUGH A NARROW BELT OF DEEP MOISTURE AND LOW 
VERTICAL WIND SHEAR (VWS) WITH A HOSTILE ENVIRONMENT ON EITHER SIDE.
ANIMATED WATER VAPOR IMAGERY DOES SHOW, HOWEVER, IMPRESSIVE RADIAL
OUTFLOW AS WELL AS CYCLING DEEP CONVECTION, SO THE SYSTEM IS
GETTING THE MOST OUT OF A MIXED AND NARROW ENVIRONMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE SOUTHERN FLANK OF THE SOUTH INDIAN
OCEAN SUBTROPICAL RIDGE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 300000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL

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: TROPICAL CYCLONE 11S (ELEVEN) WILL CHUG
STEADILY ALONG THE SOUTHERN FLANK OF THE SUBTROPICAL RIDGE TOWARDS
MAURITIUS, WITH ITS DEVELOPMENT CAPPED AT LOW TROPICAL STORM
STRENGTH.  THE ENVIRONMENT IS SIMPLY TOO NARROW AND THE RELATIVELY
DRY MODIFIED MARITIME AIR FEEDING INTO THE BOTTOM SIDE OF THE
SYSTEM WILL MAKE INTENSIFICATION AN UPHILL BATTLE THROUGHOUT THE
SYSTEMS LIFE CYCLE. A 5-10 KNOT DROP IN VWS BETWEEN TAU 24 AND 48
WILL ALLOW THE SYSTEM TO DEEPEN TO AS MUCH AS 45 KNOTS, BUT THAT
WILL BE THE EXTENT OF IT. AS MILD AS IT MAY BE, THAT DEEPENING WILL
RESULT IN A REAL THREAT OF GALE FORCE WINDS ALONG THE SOUTH COAST
OF MAURITIUS. 

MODEL DISCUSSION: TRACK GUIDANCE IS TIGHT WITH MINIMAL DISPARITY IN
BOTH ALONG TRACK AND CROSS TRACK POSITIONING. THE JTWC FORECAST IS
HEDGED JUST EQUATORWARD OF THE MULTI-MODEL CONSENSUS TOWARDS THE
ECMWF ENSEMBLE, WHICH HAS HAD A HOT HAND RECENTLY. THE INTENSITY
FORECAST IS BASED MORE HEAVILY IN STATISTICAL DYNAMICAL GUIDANCE
BUT IS NOT MUCH DIFFERENT FROM THE BULK OF GUIDANCE. THE ONE
SIGNIFICANT OUTLIER IS THE HFAS, WHICH IS THOROUGHLY UNIMPRESSED
WITH THE SYSTEMS POTENTIAL AND STAYS WELL BELOW THE REST OF THE
GUIDANCE.  

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