WDXS32 PGTW 110900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DINGANI)    
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.5S 79.3E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 643 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS CONVECTIVE
BANDING WRAPPING TIGHTLY INTO A DEFINED LOW-LEVEL CIRCULATION
CENTER (LLCC). ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
INDICATES A MORE ILL-DEFINED LLCC WITH DEEP CONVECTION DISPLACED
PRIMARILY OVER THE WESTERN SEMICIRCLE DUE TO THE NORTHEASTERLY 
VERTICAL WIND SHEAR. AN 110423Z GMI 89GHZ MICROWAVE IMAGE REVEALS A 
WEAK MICROWAVE EYE FEATURE WITH FRAGMENTED CONVECTIVE BANDING. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE MSI
AND GMI IMAGE. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON AN AVERAGE OF THE DVORAK CURRENT
INTENSITY ESTIMATES, WHICH IS CONSISTENT WITH THE MICROWAVE EYE
STRUCTURE.

INITIAL WIND RADII BASIS: SMAP DATA 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   DEMS: T3.0 - 45 KTS
   CIMSS SATCON: 54 KTS AT 110115Z
   CIMSS ADT: 53 KTS AT 110300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE 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: TROPICAL CYCLONE (TC) 13S IS FORECAST TO TURN
WEST-SOUTHWESTWARD TO SOUTHWESTWARD AS IT TRACKS ALONG THE
NORTHWESTERN PERIPHERY OF THE STR OVER THE NEXT 48 HOURS. TC 13S IS
EXPECTED TO INTENSIFY TO A PEAK INTENSITY OF 70 KNOTS DUE TO
ENHANCED POLEWARD OUTFLOW INTO AN APPROACHING UPPER-LEVEL
SHORT-WAVE TROUGH. ADDITIONALLY, VERTICAL WIND SHEAR (VWS) WILL
REMAIN LOW WITH FAVORABLE SST VALUES OF 27-28C. AFTER TAU 48, 
ENVIRONMENTAL CONDITIONS WILL DEGRADE QUICKLY AS THE SYSTEM FIRST 
INTERACTS WITH THE SHORTWAVE TROUGH THEN TRACKS UNDER STRONG 
NORTHWESTERLY FLOW WITH HIGH (30 TO 40 KNOTS) VWS. CONSEQUENTLY, TC 
13S WILL WEAKEN STEADILY THROUGH THE REMAINDER OF THE FORECAST PERIOD. 
THE SYSTEM SHOULD SLOW NEAR TAU 120 AS IT ENCOUNTERS A STRONG LOW-
LEVEL HIGH EXPECTED TO BUILD TO THE SOUTH.   

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT AGREEMENT
THROUGH TAU 48 WITH A 65NM SPREAD IN SOLUTIONS AT TAU 48. AFTER TAU
48, THERE IS INCREASING UNCERTAINTY WITH A 415NM SPREAD IN
SOLUTIONS AT TAU 120. THE BULK OF THE DETERMINISTIC AND
PROBABILISTIC GUIDANCE SUPPORTS THE JTWC FORECAST TRACK WITH A MORE
SOUTHWESTWARD TRACK. HOWEVER, ABOUT 15 PERCENT OF THE 110000Z ECMWF
ENSEMBLE SOLUTIONS, AS WELL AS THE NVGI AND AEMI TRACKERS, INDICATE
A MORE WESTWARD TO WEST-SOUTHWESTWARD TRACK TOWARD LA REUNION AND
MAURITIUS. THIS SCENARIO IS CURRENTLY ASSESSED AS UNLIKELY AS THESE
SOLUTIONS TRACK THE SYSTEM DIRECTLY INTO THE AFOREMENTIONED
UPPER-LEVEL TROUGH. DUE TO THIS, THESE SOLUTIONS GENERALLY WEAKEN
THE SYSTEM TO TROPICAL DEPRESSION STRENGTH.        

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