WDXS31 PGTW 112100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 24S (IVONE) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.8S 77.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 806 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A NEARLY
CONVECTION FREE LOW-LEVEL CIRCULATION WITH PATCHES OF DEEP
CONVECTION DEVELOPING WITHIN CONVERGENT FLOW IN THE SOUTHERN
SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
WITHIN THE EXPOSED BUT BROAD LOW-LEVEL CIRCULATION CENTER EVIDENT
IN EIR IMAGERY AND AN 111710Z NOAA-19 89 GHZ PASS. THE INITIAL
INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A
PARTIAL 111533Z METOP-B ASCAT PASS INDICATING 40-45 KT WINDS WITHIN
THE SOUTHEASTERN QUADRANT OF THE CIRCULATION. ASCAT DATA AND AN
EARLIER 111228Z SMOS PASS INDICATE A HIGHLY ASYMMETRIC WIND FIELD,
WITH SUB-GALE FORCE WINDS EVIDENT THROUGHOUT THE NORTHERN PORTION
OF THE CIRCULATION.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA (111626Z METOP-C
ASCAT) AND OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   DEMS: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS SATCON: 41 KTS AT 111623Z
   CIMSS ADT: 26 KTS AT 111800Z
   CIMSS AIDT: 33 KTS AT 111700Z
   CIMSS D-MINT: 27 KTS AT 111348Z
   CIMSS D-PRINT: 27 KTS AT 111800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG EASTWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE NORTHWEST

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 24S WILL CONTINUE TO TRACK ALONG THE
PERIPHERY OF THE CURRENT SUBTROPICAL STEERING RIDGE THROUGH THE
FORECAST PERIOD, TURNING GRADUALLY POLEWARD TOWARD THE RIDGE AXIS
OVER THE NEXT 48 HOURS AND RECURVING AND ACCELERATING SOUTHEASTWARD 
THEREAFTER. ENVIRONMENTAL CONDITIONS WILL REMAIN UNFAVORABLE IN THE 
NEAR-TERM, WITH HIGH VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT 
YIELDING A SLOW BUT STEADY WEAKENING TREND. THE WIND FIELD IS 
EXPECTED TO REMAIN ASYMMETRIC THROUGHOUT THIS PERIOD, WITH THE 
STRONGEST WINDS SITUATED TO THE SOUTH AND EAST OF THE CENTER. AFTER 
TAU 48, THE SYSTEM WILL CROSS OVER COOLER (BELOW 26C) WATER WHILE
SIMULTANEOUSLY INTERACTING WITH A MID-LATITUDE TROUGH APPROACHING
FROM THE SOUTHWEST AND UNDERGO EXTRATROPICAL TRANSITION. TC 24S
WILL CONTINUE TO WEAKEN DURING THE TRANSITION, LIKELY DISSIPATING
BELOW THE WARNING THRESHOLD INTENSITY OF 35 KTS BY TAU 96 AS IT
BECOMES A FULLY EXTRATROPICAL LOW.

MODEL DISCUSSION: NUMERICAL MODEL TRACK FORECAST GUIDANCE IS IN
VERY GOOD AGREEMENT THROUGH TAU 72, WHILE SPREAD INCREASES SLIGHTLY
DUE TO DIFFERING DEPICTIONS OF STORM ACCELERATION DURING THE
SOUTHEASTWARD RECURVATURE THEREAFTER. INTENSITY FORECAST
GUIDANCE, PARTICULARLY DYNAMICAL MODELS INCLUDING HAFS AND
COAMPS-TC, INDICATES A SLOW BUT STEADY WEAKENING TREND WITH SOME
BAROCLINIC SUPPORT PROVIDED DURING EXTRATROPICAL TRANSITION DESPITE
A SUBOPTIMAL INTERACTION BETWEEN THE SYSTEM AND THE
DEVELOPING MID-LATITUDE TROUGH.

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