WDXS32 PGTW 150900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DINGANI) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.7S 69.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 1187 NM SOUTH OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC) WITH FRAGMENTED FEEDER BANDS
WRAPPING INTO THE CORE. THE SYSTEM HAS BECOME DECOUPLED FROM THE
MAIN BULK OF CONVECTION WHICH IS NOW COMPLETELY DISPLACED POLEWARD.
A 150508Z ASCAT-B IMAGE SHOWS THE LLCC QUITE WELL, HOWEVER, A
MAJORITY OF THE EASTERN PERIPHERY IS NOT VIEWABLE. THIS IMAGE ALSO
SHOWS 35 KNOT WINDS DOMINATING IN ALL QUADRANTS WITH THE EXCEPTION
OF THE NORTHWEST QUADRANT WHERE 30 KNOT WINDS PREDOMINATELY REIGN.
MOREOVER, THERE ARE 40-45 KNOT WIND BARBS NOTED IN THE SOUTHERN
PERIPHERY WHICH LENDS TO MEDIUM CONFIDENCE IN THE JTWC INITIAL
INTENSITY OF 50 KNOTS. THE INITIAL WIND RADII WAS ALSO ADJUSTED
BASED ON THIS ASCAT IMAGE. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THIS ASCAT PASS, AS WELL AS THE AFOREMENTIONED
MSI. ENVIRONMENTAL ANALYSIS REVEALS TC DINGANI IS IN AN UNFAVORABLE
ENVIRONMENT FOR FURTHER TROPICAL DEVELOPMENT CHARACTERIZED BY VERY
LITTLE OUTFLOW ALOFT, STRONG (30-35 KTS) VERTICAL WIND SHEAR (VWS),
AND RELATIVELY COOLER (25-26 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 150508Z SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO
THE EAST-SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 37 KTS AT 150416Z
   CIMSS ADT: 25 KTS AT 150700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 25-26 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 DINGANI CONTINUES ITS SOUTH-SOUTHWESTWARD
TRACK AS IT IS NOW APPROACHING COOLER WATERS. TC 13S WILL CONTINUE
THIS TRAJECTORY AS IT DECREASES IN INTENSITY DUE TO INCREASING VWS,
CONTINUAL DRY AIR ENTRAINMENT, AND DECLINING SSTS. BY TAU 24 TC
DINGANI WILL BEGIN TO FALL UNDER THE INFLUENCE OF THE SUBTROPICAL
JET AND TURN TO A SOUTHEASTWARD TRACK, ALL THE WHILE CONTINUING TO
DECREASE IN INTENSITY AND COMPLETELY DISSIPATE BY TAU 48.

MODEL DISCUSSION: THE JTWC MODEL TRACK CONSENSUS REMAINS IN TIGHT
AGREEMENT WITH A GRADUAL SPREAD TO 45 NM AT TAU 24. AFTERWARDS, THE
SPREAD INCREASES TO 60 NM BY TAU 48. ALL MEMBERS AGREE ON THE
SOUTHEASTWARD SHIFT IN TRACK BY TAU 24 AS THE SYSTEM SUCCUMBS TO
THE PREVAILING WESTERLIES. THE INTENSITY MODEL GUIDANCE IS ALSO IN
TIGHT AGREEMENT WITH ALL MEMBERS SUPPORTIVE OF A DISSIPATION
SCENARIO FROM HERE ON OUT. BECAUSE OF THIS, THE JTWC FORECAST TRACK
AND FORECAST INTENSITY ARE BOTH SET WITH HIGH CONFIDENCE THROUGHOUT
THE FORECAST PERIOD.

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