WDXS31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DJOUNGOU)
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.5S 76.2E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 717 NM SOUTH-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 13S (DJOUNGOU) EXHIBITING A TIGHTENING SYMMETRIC EYE OF
20NM DIAMETER AND SMOOTH CIRRUS CANOPY ALOFT (168NM DIAMETER).
ROBUST SPIRAL BANDING PERSISTS THROUGHOUT THE EASTERN PERIPHERY OF
THE SYSTEM WITH INTERMITTENT OVERSHOOTING CLOUD TOPS THROUGHOUT. A
180406Z MHS 89GHZ SATELLITE MICROWAVE IMAGE CAPTURED A SLIGHT OFFSET 
OF THE LOW LEVEL CIRCULATION CENTER (LLCC) AND UPPER LEVEL EYE 
FEATURE, SHOWING THE EYE FEATURE TO BE 30NM EAST OF THE LLCC AND 
SUGGESTING AN EASTWARD TILTING VORTEX WITH HEIGHT. THE ENVIRONMENT IS 
ASSESSED AS HIGHLY FAVORABLE HAVING SIGNIFICANT DIVERGENCE ALOFT, 
WARM 
(29-30C) SEAS SURFACE TEMPERATURES (SST) OFFSET BY MODERATE (15-
20KTS) 
VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE SYMMETRIC EYE FEATURE OBSERVED IN A GOES-IO 
VISIBLE SATELLITE IMAGE. THE INITIAL INTENSITY OF 120 KTS IS ASSESSED 
WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND OBJECTIVE 
INTENSITY 
ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SMOS DATA 

CURRENT STEERING MECHANISM: NEAR EQUATORIAL RIDGE (NER) TO THE
NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   DEMS: T6.5 - 127 KTS
   FMEE: T5.5 - 102 KTS
   FIMP: T5.5 - 102 KTS
   CIMSS ADT: 117 KTS AT 180630Z
   CIMSS AIDT: 111 KTS AT 180630Z
   CIMSS DPRINT: 108 KTS AT 180700Z
   CIMSS SATCON: 117 KTS AT 180630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 13S IS FORECAST TO TRACK ALONG THE
SOUTHWESTERN PERIPHERY OF THE NEAR EQUATORIAL RIDGE TO THE
NORTHEAST OF THE SYSTEM THROUGHOUT THE FORECAST PERIOD, STEERING
THE SYSTEM SOUTHEASTWARD THROUGH TAU 48 AND THEN GRADUALLY TURNING
TO AN EASTWARD TRACK BY TAU 72. IN GENERAL, THE FAVORABLE
ENVIRONMENT BEGINS TO GRADUALLY BECOME UNFAVORABLE, STARTING WITH A
RISE IN VWS (25-30KTS BY TAU 12). SST IS ANTICIPATED TO STEADILY
DROP FROM 30C (TAU 00) TO 22C (TAU 72). UPPER LEVEL DIVERGENCE IS
FORECAST TO SHARPLY CUT OFF BETWEEN TAU 36 AND TAU 48, ATTRIBUTED
TO SIGNIFICANT DRY AIR ENTRAINMENT STARTING NEAR TAU 24. IN SUCH, A
RAPID WEAKENING TREND IS FORECAST FROM TAU 12 TO TAU 72. THE SYSTEM
IS FORECAST TO BEGIN SUBTROPICAL TRANSITION NEAR TAU 48 AND BE 
SUBTROPICAL BY TAU 72.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN EXCEPTIONAL
AGREEMENT REGARDING BOTH TRACK AND INTENSITY. THE JTWC TRACK
FORECAST IS PLACED WITH HIGH CONFIDENCE WITH A CROSS-TRACK SPREAD
AT TAU 72 OF JUST 107 NM. INTENSITY GUIDANCE SUGGESTS THE SYSTEM
HAS LIKELY REACHED PEAK INTENSITY, WITH ONLY ONE JTWC CONSENSUS
MEMBER (COAMPS-TC) SUGGESTING A POSSIBLE SLIGHT (5 KTS) RISE FROM
TAU 00 TO TAU 12. FOR THE REMAINDER OF THE FORECAST PERIOD,
GUIDANCE INDICATES A RAPID WEAKENING TREND BUT WITH A 30 KT
SPREAD IN GUIDANCE BY TAU 72. FOR THIS REASON, THE JTWC INTENSITY 
FORECAST IS PLACED WITH MEDIUM CONFIDENCE. 

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