WDXS31 PGTW 161500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IALY) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.1S 52.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 656 NM NORTH-NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 24S (IALY) CONSOLIDATING WITH SIGNIFICANT DEEP CONVECTIVE
BANDING TO THE SOUTH AND WEST WRAPPING INTO THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE SYSTEM IS CURRENTLY BEING STEERED TO
THE SOUTHWEST ON THE PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO THE
SOUTH. A 160607Z METOP-B ASCAT HIGHLIGHTED THE ASYMMETRICAL NATURE
OF THE WIND FIELD, CONVEYING WIND SPEEDS AS WEAK AS 15-20KTS ON THE
NORTHEASTERN PERIPHERY OF THE SYSTEM AND ELEVATED SPEEDS EXCEEDING
WARNING CRITERIA TO THE SOUTHWEST. ENVIRONMENTAL CONDITIONS ARE
FAVORABLE GIVEN THE MODERATE POLEWARD OUTFLOW, 29-30C SEA SURFACE
TEMPERATURES, AND MODERATE VERTICAL WIND SHEAR OF 10-15KTS. THE
INITIAL POSITION WAS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
ANIMATED MSI, THE PREVIOUSLY MENTIONED ASCAT-B IMAGE, AND A 160942Z
89GHZ AMSR2 IMAGE DEPICTING DEEP CONVECTIVE BANDING FROM THE
SOUTHWEST WRAPPING IN TO THE LLCC. THE INITIAL INTENSITY WAS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE PREVIOUSLY MENTIONED
SCATTEROMETRY DATA AND THE AGENCY FIXES BELOW.

INITIAL WIND RADII BASIS: 160940Z AMSR2 WIND SPEED DATA AND
OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: STR TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T2.0 - 30 KTS
   FMEE: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL CYCLONE 24S IS FORECAST TO CONTINUE
TRACKING WESTWARD SLOWLY OVER THE NEXT 48 HOURS ON THE NORTHERN
PERIPHERY OF A STR TO THE SOUTH. BEYOND TAU 48, THE SYSTEM IS
FORECAST TO TRACK IN A NORTHWARD DIRECTION UNDER THE STEERING
INFLUENCE OF A NEAR EQUATORIAL RIDGE LOCATED OVER THE CENTRAL
AFRICAN CONTINENT. IN THE NEAR-TERM, TC 24S WILL INTENSIFY THROUGH THE 
FIRST 72 HOURS DUE TO GENERALLY FAVORABLE CONDITIONS OF LOW TO 
MODERATE VERTICAL WIND SHEAR, 29-30C SSTS, AND MODERATE POLEWARD 
OUTFLOW, OVERCOMING ASYMMETRY OF THE CURRENT WIND FIELD. HOWEVER, 
BETWEEN TAU 72 AND 120 MID- AND UPPER-LEVEL VERTICAL WIND SHEAR IS 
EXPECTED TO DECAPITATE THE SYSTEM, RESULTING IN FULL DISSIPATION BY 
THE END OF THE FORECAST PERIOD. DRY AIR ENTRAINMENT WILL ENSUE, 
ACCOMPANIED BY A REDUCTION OF OUTFLOW AS SIGNIFICANT STRAIGHT-LINE 
UPPER-LEVEL FLOW WILL CREATE AN UNFAVORABLE ENVIRONMENT.

MODEL DISCUSSION: GLOBAL DETERMINISTIC MODEL GUIDANCE IS IN GOOD
AGREEMENT THAT TC 24S WILL TRACK WESTWARD THROUGH THE FIRST 48
HOURS BEFORE ALTERING COURSE NORTHWARD THROUGH THE END OF THE
FORECAST PERIOD. HOWEVER, THERE IS MILD DISAGREEMENT BEYOND TAU 72
AS TO HOW SHARPLY IT TURNS NORTH AND WHETHER OR NOT THE LONG-TERM
TRACK WILL BE DUE NORTH, NORTH-NORTHEAST, OR NORTH-NORTHWEST. THE
JTWC INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL
CONTINUE TO INTENSIFY UP TO SPEEDS OF POTENTIALLY 40-60KTS BEFORE
BECOMING OVERWHELMED BY VERTICAL WIND SHEAR AND DISSIPATING BY TAU
120.

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