WDXS31 PGTW 170300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IALY) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 9.1S 51.9E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 641 NM NORTH-NORTHEAST OF ANTANANARIVO,
MADAGASCAR
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) THAT IS
TUCKED UNDER THE NORTHEASTERN CORNER OF THE PRIMARY CONVECTIVE
CELL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
A 162208Z AMSR2 89GHZ MICROWAVE IMAGE WHICH SHOWED A MOMENTARILY
FULLY EXPOSED LLCC WITH TIGHTLY WRAPPING LOW LEVEL CLOUD LINES IN
ALL FOUR QUADRANTS. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON A RECENT 161755Z PARTIAL ASCAT-C
SCATTEROMETERY PASS WHICH SHOWED A MODERATE FIELD OF 35KT WINDS TO
THE WEST-SOUTHWEST OF THE LLCC AND 15-20KT WINDS TO THE NORTHWEST.
FURTHERMORE, ADT, AIDT, D-PRINT AND ALL AGENCY DVORAK INTENSITY
ESTIMATES ALSO SUPPORT 35-40KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL (STR) TO THE SOUTH 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   DEMS: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS ADT: 37 KTS AT 162100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 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 FORECAST TO CONTINUE
MEANDERING GENERALLY WESTWARD UNDER THE STEERING INFLUENCE OF THE
STR TO THE SOUTH. AS THE SYSTEM PROPAGATES WESTWARD, MODERATE
VERTICAL WIND SHEAR (VWS) AND MID-LEVEL DRY AIR ENTRAINMENT WILL
GENERALLY NEGATE WARM SSTS AND FAVORABLE UPPER-LEVEL OUTFLOW,
RESULTING IN STAGNATING INTENSITIES THROUGH TAU 24. AS THE STR TO
THE SOUTH REORIENTS AND BREAKS DOWN, STEERING INFLUENCE SHIFTS TO A
BUILDING NEAR-EQUATORIAL RIDGE (NER) TO THE WEST. AS THIS SHIFTS
TAKES PLACE AND THE SYSTEM IS DEFLECTED EQUATORWARD, MOMENTARILY
LOWER VWS VALUES AND INCREASED UPPER-LEVEL OUTFLOW WILL RESULT IN
LIMITED INTENSIFICATION TO AROUND 45KTS AND POSSIBLY 50KTS BY TAU
48. BY TAU 72, THE PARTY IS OVER, AS VWS, DRY AIR ENTRAINMENT AND
HEAVILY REDUCED OUTFLOW RESULTS IN STEADY WEAKENING THROUGH
DISSIPATION NEAR TAU 120 AS THE SYSTEM ACCELERATES EQUATORWARD.

MODEL DISCUSSION: WITH THE EXCEPTION OF NVGM AND COAMPS-TC (NVGM
VERSION), THE BULK OF THE MODEL GUIDANCE IS IN SOLID AGREEMENT
THROUGH TAU 36 WITH A 80NM SPREAD IN MEMBER GUIDANCE. AFTER TAU 36,
NOT ONLY DOES NVGM SAUNTER OFF MORE WESTWARD THAN THE BULK OF THE
MODELS BUT ALONG TRACK SPREADING ALSO SLIGHTLY INCREASES. ECMWF AND
ITS ENSEMBLE INDICATE A SLOWER EQUATORWARD TRACK SPEED THAN THE
REMAINING MEMBERS THROUGH TAU 120. FOR THESE REASONS THE JTWC TRACK
FORECAST IS PLACED INITIALLY WITH HIGH CONFIDENCE AND WITH MEDIUM
CONFIDENCE THEREAFTER. RELIABLE MODEL INTENSITY GUIDANCE IS IN
OVERALL MODERATE AGREEMENT WITH DECAY-SHIPS INCREASING THE SYSTEM
TO 55KTS WHILE GFS, HAFS AND COAMPS-TC WEAKEN THE SYSTEM SLOWLY
AFTER TAU 36. FOR THESE REASONS THE JTWC INTENSITY FORECAST IS
PLACED CLOSE TO THE CONSENSUS WITH MEDIUM CONFIDENCE.

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