WDXS32 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 22S (HALIMA) WARNING 
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.5S 84.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 1009 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
MEDIUM-SIZED SYSTEM WITH ITS ASSOCIATED CONVECTION AND CIRRUS CANOPY
SHEARED SOUTHEASTWARD, PARTIALLY EXPOSING THE LOW LEVEL
CIRCULATION (LLC). THE CENTRAL CONVECTION, ALBEIT OFFSET FROM THE
LLC, HAS EXPANDED AND DEEPENED OVER THE LAST 6-12 HOURS. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
PARTIALLY-EXPOSED LLC LINED UP WITH A DEFINED MICROWAVE LLC IN THE
311106Z SSMIS 91GHZ IMAGE. THE INITIAL INTENSITY OF 45KTS IS BASED
ON THE HIGHER END OF AGENCY AND AUTOMATED DVORAK ESTIMATES,
CORROBORATED BY A 310804Z AMSR2 WINDSPEED DATA, AND REFLECTS THE
RECENT IMPROVEMENT IN THE CENTRAL CONVECTION. ANALYSIS INDICATES A
MARGINAL ENVIRONMENT WITH THE WARM SST AND STRONG POLEWARD OUTFLOW
OFFSET BY MODERATE VWS AND COLD DRY AIR INTRUSION AT THE LOW
LEVELS. THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF THE
EASTERN EXTENSION OF THE NER TO THE NORTHWEST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: EASTERN EXTENSION OF THE NEAR
EQUATORIAL RIDGE (NER) TO THE NORTHWEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   FMEE: T3.0 - 45 KTS
   FIMP: T3.0 - 45 KTS
   CIMSS SATCON: 42 KTS AT 310800Z
   CIMSS ADT: 33 KTS AT 310915Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECAST TRACK EXTENDED TO TAU 72,
OTHERWISE, NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY. 

FORECAST DISCUSSION: TC HALIMA WILL TRACK EAST-NORTHEASTWARD OVER
THE NEXT 12HRS AS THE NER RECEDES WESTWARD. AFTER TAU 12, A
BUILDING STR TO THE SOUTHWEST WILL ASSUME STEERING AND DRIVE THE
SYSTEM GENERALLY WESTWARD AFTER A SHARP COUNTER-CLOCKWISE U-TURN.
THE MARGINAL CONDITIONS WILL BECOME MORE UNFAVORABLE ALONG THE
FORECAST TRACK WITH THE PERSISTENT DRY AIR INTRUSION AND INCREASING
VWS DUE TO THE STORM MOTION BECOMING OUT-OF-PHASE WITH THE UPPER
LEVEL WIND FLOW. THIS WILL SLOWLY ERODE THE SYSTEM TOWARD
DISSIPATION BY TAU 72, POSSIBLY SOONER.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL AGREEMENT WITH
THE WESTWARD REVERSAL IN THE FORECAST TRACK; HOWEVER, THERE ARE
SIGNIFICANT DIFFERENCES IN THE TIMING OF THE U-TURN. THIS, PLUS THE
UNCERTAINTY IN THE FORECAST INTENSITY, LENDS LOW CONFIDENCE IN THE
JTWC TRACK FORECAST THAT IS LAID CLOSE TO THE MODEL CONSENSUS. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   INTENSITY 0 - 72 HR: LOW//
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