WDXS31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IALY) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 8.8S 50.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 629 NM NORTH-NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE
LOW-LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL CYCLONE 24S FULLY
EXPOSED AS SIGNIFICANT NORTHEASTERLY VERTICAL WIND SHEAR (VWS) HAS
FULLY DECAPITATED THE SYSTEM OVER THE LAST TWELVE HOURS. THE SYSTEM
REACHED A PEAK INTENSITY OF 45KTS BETWEEN 161800Z AND 170600Z
BEFORE BEGINNING TO WIND DOWN. THE SYSTEM HAS BEGUN TO TRACK ON A
WEST-NORTHWESTWARD TRACK WHILE INFLUENCED BY MID- AND LOW-LEVEL
SOUTHEASTERLY FLOW AND A SUBTROPICAL RIDGE TO THE SOUTHEAST. THE
INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE BASED ON
ANIMATED MSI AND A 161025Z AMSR-2 89GHZ IMAGE DEPICTING A
CONSOLIDATED LLCC WITH PATCHY DEEP CONVECTION TO THE SOUTHWEST. THE
INITIAL INTENSITY WAS ASSESSED WITH HIGH CONFIDENCE BASED ON AGENCY
AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE AND OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: STR TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   FMEE: T3.0 - 45 KTS

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

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TC 24S HAS WEAKENED UNDER STRONGER
THAN ANTICIPATED VERTICAL WIND SHEAR AND IS EXPECTED TO CONTINUE
WEAKENING. FORECAST INTENSITIES HAVE DECREASED AND DISSIPATION IS
NOW EXPECTED BY TAU 48.

FORECAST DISCUSSION: TC 24S IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD ON THE NORTHWESTERN PERIPHERY OF A STR TO THE
SOUTHEAST THROUGH THE NEXT 36 HOURS. THE SYSTEM IS ANTICIPATED TO
GRADUALLY TRANSITION TO A NORTH-NORTHWESTWARD TRACK BETWEEN TAU 36
AND 48 AS THE SYSTEM WEAKENS AND COMES UNDER THE STEERING INFLUENCE
OF A LOW-LEVEL RIDGE TO THE SOUTHWEST. TC 24S IS EXPECTED TO
PERSIST AT 40KTS OVER THE NEXT 24 HOURS BUT WEAKEN STEADILY
THEREAFTER AS VWS INCREASES TO 20-25KTS, LEADING TO DISSIPATION BY
TAU 48. STRAIGHT LINE UPPER-LEVEL FLOW WILL ALSO RESULT IN AN
UNFAVORABLE OUTFLOW PATTERN. IF THE VWS CONTINUES TO IMPACT TC 24S
AS SIGNIFICANTLY AS IT HAS OVER THE LAST 12 HOURS, THE SYSTEM COULD
DISSIPATE MORE QUICKLY THAN REFLECTED IN THE CURRENT FORECAST.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TC 24S WILL TRACK IN A GENERALLY NORTHWESTWARD DIRECTION WITH
SLIGHT DEVIATIONS RESULTING FROM VARYING ORIENTATIONS OF THE
STEERING RIDGE. THE MINOR DEVIATIONS RESULT IN A CROSS-TRACK SPREAD
OF 140NM BY THE END OF THE FORECAST PERIOD. THE JTWC INTENSITY
FORECAST IS CONSISTENT WITH MESOSCALE MODEL GUIDANCE, INCLUDING
HAFS AND COAMPS-TC, WHICH INDICATES A STEADY WEAKENING TREND
CONSISTENT WITH EXPECTED UNFAVORABLE UPPER-LEVEL CONDITIONS,
COUNTER TO AVAILABLE SHIPS GUIDANCE WHICH SUGGESTS AN UNREALISTIC
INTENSIFICATION TREND.

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