WDXS31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11S (ELEVEN) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.6S 75.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 473 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 11S WITH AN ELONGATED, PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION ALONG THE
SOUTHWESTERN PERIPHERY. THE VORTEX CONTINUES TO BE TILTED WITH
HEIGHT AS IS APPARENT BY THE OFFSET CONVECTION. ENVIRONMENTAL
ANALYSIS INDICATES THAT 11S IS IN A MARGINAL ENVIRONMENT
CHARACTERIZED BY MODERATE POLEWARD OUTFLOW ALOFT AND WARM (28-29
C) SEA SURFACE TEMPERATURES OFFSET BY MODERATE TO HIGH (20-25 KTS)
VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON A 291303Z SSMIS 91 GHZ
MICROWAVE IMAGE SHOWING THE LOW-LEVEL CLOUD LINES. THE INITIAL
INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T2.5 - 35 KTS
   CIMSS SATCON: 36 KTS AT 291100Z
   CIMSS ADT: 32 KTS AT 291200Z
   CIMSS AIDT: 33 KTS AT 291200Z
   CIMSS DPRINT: 31 KTS AT 291200Z
   CIMSS DMINT: 27 KTS AT 291203Z
   

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: TILTED VORTEX WITH HEIGHT AND DRY AIR ENTRAINMENT
WITHIN THE NORTHERN PERIPHERY.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 11S IS FORECAST TO TRACK SOUTHWESTWARD, ALONG
THE NORTHWESTERN PERIPHERY OF THE STR, THROUGH TAU 24. AFTER TAU
24, A SECOND STR IS EXPECTED TO BUILD SOUTH OF THE CIRCULATION
WHICH WILL DRIVE THE SYSTEM MORE WESTWARD. NEAR TAU 48, 11S WILL
ROUND THE STR AND TRACK MORE SOUTHWESTWARD AGAIN AS IT HEADS TOWARD
MAURITIUS. REGARDING INTENSITY, 11S IS EXPECTED TO CONSOLIDATE A
BIT OVER THE NEXT 12 HOURS, BACK UP TO 35 KTS. THIS WILL MAINTAIN
THROUGH TAU 36 AS THE ENVIRONMENT CONTINUES TO BE MARGINAL. AFTER
TAU 36, VERTICAL WIND SHEAR IS FORECAST TO SLIGHTLY DROP AND DRY
AIR ENTRAINMENT WILL LESSEN. THIS WILL ALLOW 11S TO GRADUALLY
INTENSIFY THROUGH THE REMAINDER OF THE FORECAST PERIOD TO AROUND 45
KTS. THE ABILITY OF THE VORTEX TO BECOME VERTICALLY ALIGNED WILL BE
A MAJOR FACTOR ON IF 11S CAN INTENSIFY. IF IT IS UNABLE TO ALIGN,
IT MAY SHALLOW OUT AND DISSIPATE MUCH SOONER. 


MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
CONCERNING THE TRACK OF 11S. CROSS-TRACK SPREAD AT TAU 72 IS 110
NM, WHICH OPENS UP TO 350 NM AT TAU 120. THE JTWC TRACK FORECAST IS
PLACED CLOSE TO CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72 AND
MEDIUM THEREAFTER. INTENSITY GUIDANCE CONTINUES TO BE IN POOR
AGREEMENT. GFS SUGGESTS CONTINUOUS GRADUAL WEAKENING AFTER TAU 12
WHILE HWRF AND COAMPS-TC SUGGEST INTENSIFICATION TO AROUND 50 KTS
AT TAU 72. AFTER TAU 72, HWRF CONTINUES TO INTENSIFY THE SYSTEM TO
AROUND 80 KTS AT TAU 120. THE JTWC INTENSITY FORECAST IS PLACED IN
THE MIDDLE, CLOSER TO CONSENSUS, WITH LOW CONFIDENCE THROUGHOUT THE
FORECAST PERIOD. 

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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