WDXS31 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IVONE) WARNING NR 
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.8S 66.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 568 NM EAST-SOUTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED AND HIGHLY ELONGATED LOW LEVEL CIRCULATION CENTER (LLCC).
NASCENT CONVECTION IS ONCE AGAIN DEVELOPING JUST SOUTHEAST OF THE
LLCC BUT IT REMAINS TO BE SEEN WHETHER OR NOT THIS CONVECTION WILL
PERSIST. IN LIGHT OF THE HIGH NORTHWESTERLY SHEAR VECTOR, IT IS
UNLIKELY THE CONVECTION WILL BE STRONG ENOUGH TO EXPAND UPSHEAR AND
RE-COVER THE LLCC. A 131632Z ASCAT-B PASS REVEALED AN ELONGATED
CIRCULATION ORIENTED ALONG A NORTHWEST TO SOUTHEAST AXIS, WITH A
SMALL, FULLY ENCLOSED, CIRCULATION CENTER IN THE SOUTHERN EXTENT OF
THE OVERALL LARGER ROTATION. WINDS WERE VERY LIGHT ACROSS THE
NORTHERN HALF OF THE CIRCULATION AND GALE-FORCE WIND OF 35 KNOTS
ACROSS THE MAJORITY OF THE SOUTHERN HEMISPHERE OF THE CIRCULATION.
ADDITIONALLY, THE SCATTEROMETER DATA INDICATES THE RMW HAS
DECREASED TO LESS THAN 100NM OVER THE PAST 24 HOURS. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION
OF THE CENTER DEFINED IN THE ASCAT PASS. THE INITIAL INTENSITY IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA NOTED ABOVE
AND REMAINS CONSISTENT WITH THE CIMSS AIDT, SATCON AND D-MINT
ESTIMATES. THE ENVIRONMENT IS UNFAVORABLE, WITH MARGINAL SSTS, HIGH
NORTHWESTERLY SHEAR, AND DRY MID-LEVEL AIR OFFSETTING THE ROBUST
POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   DEMS: T1.5 - 25 KTS
   CIMSS SATCON: 42 KTS AT 131530Z
   CIMSS ADT: 25 KTS AT 131730Z
   CIMSS AIDT: 34 KTS AT 131730Z
   CIMSS D-MINT: 32 KTS AT 131407Z
   CIMSS D-PRINT: 27 KTS AT 131730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: CONVERGENT UPPER-LEVEL FLOW TO THE NORTHWEST AND
MID-LEVEL DRY AIR INTRUSION. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 24S IS TRACKING
SOUTHWARD, NEARING THE AXIS OF THE SUBTROPICAL RIDGE (STR) TO THE
EAST. THE SYSTEM IS EXPECTED TO REACH THE RIDGE AXIS WITHIN THE
NEXT 12 HOURS, QUICKLY ROUND THE RIDGE AND THEN ACCELERATE
SOUTHEASTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. IN THE
UPPER-LEVELS, A DEEP-LAYER TROUGH IS SITUATED JUST WEST OF TC 24S
AND MOVING STEADILY EASTWARD. THE STRONGLY DIVERGENT FLOW AHEAD OF
THE TROUGH IS SUPPORTING DEVELOPMENT OF A ROBUST POLEWARD OUTFLOW
CHANNEL, WHICH IS PROVIDING A BURST OF MINIMALLY SUPPORTIVE
ENVIRONMENTAL SUPPORT. GLOBAL AND MESOSCALE MODELS REMAIN
CONSISTENT IN SHOWING A TIGHTENING OF THE WIND FIELD AND SLIGHT
INTENSIFICATION AS THE SYSTEM TAPS INTO THE ROBUST DIVERGENT
OUTFLOW AHEAD OF THE TROUGH. THUS, THE FORECAST CALLS FOR A BRIEF
PERIOD OF INTENSIFICATION, UP TO 40 KNOTS, THROUGH THE NEXT 24
HOURS. THE TROUGH PASSES OVER AND EAST OF TC 24S WITHIN THE NEXT 24
HOURS, AND AFTER PASSAGE, CONVERGENT FLOW ALOFT AND SIGNIFICANT DRY
AIR WILL QUICKLY ENGULF THE SYSTEM AND LEAD TO STEADY WEAKENING.
SIMULTANEOUSLY, THE SYSTEM BEGINS EXTRATROPICAL TRANSITION (ETT) AS
IT BEGINS INTERACTION WITH THE UPPER-LEVEL TROUGH, WITH COMPLETION
OF ETT EXPECTED BY TAU 36. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
AGREEMENT, WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD. THE JTWC
FORECAST IS SITUATED NEAR THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS MORE MIXED, WITH THE COAMPS-TC
AND GFS INDICATING INTENSIFICATION UP TO 40 KNOTS FOLLOWED BY SLOW
WEAKENING, WHILE THE HWRF AND HAFS-A INDICATE STEADY WEAKENING FROM
THE BEGINNING OF THE FORECAST. THE JTWC FORECAST IS SITUATED CLOSE
TO THE MORE AGGRESSIVE MODELS, WITH MEDIUM CONFIDENCE. 

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