WDXS31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IALY) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.0S 49.2E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 661 NM NORTH OF ANTANANARIVO, MADAGASCAR
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
FADING REMNANTS OF SPURIOUS CONVECTION DUE PRIMARILY TO DIURNAL
FORCINGS. AS THIS CONVECTION IS SHEARED TO THE SOUTHWEST, THE
LOW-LEVEL CIRCULATION IS BECOMING INCREASINGLY EXPOSED. THIS IS
FURTHER EXACERBATED BY THE ONGOING ENTRAINMENT OF DRY AIR INTO THE
MID-UPPER LEVELS OF THE CIRCULATION. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON A RECENT 180021Z 89GHZ SSMIS COLOR
COMPOSITE MICROWAVE IMAGE WHICH SHOWS A MOSTLY EXPOSED LLCC WITH
LIMITED DEEP CONVECTION TO THE NORTHWEST. THE INITIAL INTENSITY OF
40 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
PREPONDERANCE OF INTENSITY ESTIMATES, INCLUDING CIMSS ADT, AIDT,
DPRINT, DMINT AND AGENCY DVORAK INTENSITY ESTIMATES, ALL OF WHICH
INDICATE 38-44KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   DEMS: T2.5 - 35 KTS
   FMEE: T3.0 - 45 KTS
   CIMSS SATCON: 44 KTS AT 172218Z
   CIMSS ADT: 45 KTS AT 180000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TC 24S (IALY) IS FORECASTED TO CONTINUE
TRACKING NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO
THE SOUTHEAST. OVER THE NEXT 24 HOURS, PRIMARY STEERING CONTROL
SHIFTS TO A NEAR EQUATORIAL RIDGE (NER) CENTERED OVER SOUTHERN
AFRICA. AS THIS HAPPENS, 24S WILL TRANSITION TO AN EQUATORWARD
TRACK THROUGH THE FORECAST PERIOD. IN TERMS OF INTENSITY, THE NEXT
24 HOURS WILL LIKELY BE UNEVENTFUL, AS MODERATE VERTICAL WIND SHEAR
(VWS), DRY AIR ENTRAINMENT, SOLID UPPER LEVEL OUTFLOW AND WARM SSTS
BATTLE FOR DOMINANCE. AFTER TAU 24, A VICTOR IS CROWNED AS DRY AIR
ENTRAINMENT, BUILDING VWS AND DECREASING OUTFLOW CONSPIRE TO WEAKEN
AND EVENTUALLY DISSIPATE THE SYSTEM BY TAU 48 AND POSSIBLY SOONER.

MODEL DISCUSSION: WITH FEW EXCEPTIONS TO THE LEFT AND RIGHT OF THE
CONSENSUS TRACK, ALL AVAILABLE MODEL GUIDANCE ECHOES THE JTWC
FORECAST TRACK. FOR THIS REASON, THE JTWC TRACK FORECAST IS PLACED
WITH OVERALL MEDIUM CONFIDENCE. WITH THE EXCEPTION OF DECAY-SHIPS
(NVGM VERSION), RELIABLE MODEL INTENSITY GUIDANCE IS IN GOOD
AGREEMENT THAT 24S WILL GENERALLY STAGNATE THROUGH TAU 24 AFTER
WHICH THE SYSTEM WEAKENS UNTIL DISSIPATION BY TAU 48. FOR THIS
REASON, THE JTWC INTENSITY FORECAST IS PLACED WITH HIGH CONFIDENCE.

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