WDXS31 PGTW 170900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DJOUNGOU)
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.2S 68.9E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 585 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 13S (DJOUNGOU) EXHIBITING PERSISTENT, CENTRALIZED DEEP
CONVECTION PARTIALLY OBSCURING THE LOW LEVEL CIRCULATION CENTER
OVER THE PAST 12 HOURS. A 170419Z MHS 89GHZ MICROWAVE IMAGE REVEALS
A FORMATIVE MICROWAVE EYE CLOSED OFF IN ALL BUT THE SOUTHEASTERN
SECTION WITH SPIRAL BANDING WRAPPING INTO CENTER OF CIRCULATION. AS
NUMERICAL MODELING GUIDANCE SUGGESTS, A RELATIVELY DRY AIR MASS
WEST-SOUTHWEST OF THE LLCC HAS BEGUN TO ENTRAIN THE WESTERN
PERIPHERY OF THE SYSTEM, AS EVIDENCE BY A PARTIAL CLEARING OF
CLOUDS IN THE MIDDLE TO UPPER LAYERS OF THE ATMOSPHERE. DESPITE
THE DRY AIR, HOWEVER, THE ENVIRONMENT IS OVERALL VERY FAVORABLE FOR
INTENSIFICATION TO OCCUR WITH LOW (0-5KTS) VERTICAL WIND SHEAR
(VWS), WARM (29-30C) SEA SURFACE TEMPERATURES (SST), AND
EXCEPTIONAL POLEWARD DIVERGENCE ALOFT. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A 170511Z METOP-B
SCATTEROMETRY IMAGE. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED SCATTEROMETRY
DATA AND THE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NER NORTHEAST OF THE LLCC

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 61 KTS AT 170630Z
   CIMSS AIDT: 55 KTS AT 170700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 13S IS FORECAST TO TRACK ALONG THE
SOUTHWESTERN PERIPHERY OF A NEAR EQUATORIAL RIDGE THROUGHOUT THE
FORECAST INTERVAL.  FROM TAU 00 TO TAU 36, THE STEERING INFLUENCE
PRESENTED WILL SLOWLY TURN THE SYSTEM FROM AN EASTWARD (TAU 00)
TRACK TO A SOUTHEASTWARD TRACK (TAU 36). DURING THIS TIME, THE TC IS
FORECAST TO UNDERGO RAPID INTENSIFICATION IN A VERY FAVORABLE
ENVIRONMENT, PEAKING BETWEEN TAU 24 AND TAU 36 AT NEAR 110KTS.
BEGINNING NEAR TAU 36, HIGH (OVER 30KTS) VWS, DECOUPLING OF UPPER
LEVEL DIVERGENCE SUPPORT, FALLING SST (25C BY TAU 96), AND DRY AIR
ENTRAINMENT OF THE CORE VORTEX (TAU 48 TO TAU 96) ARE ANTICIPATED TO
QUICKLY WEAKEN THE SYSTEM. THE TC IS FORECAST TO TRANSITION TO
A SUBTROPICAL SYSTEM BETWEEN TAU 72 AND TAU 96.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN EXCEPTIONAL
AGREEMENT REGARDING THE TRACK AND GOOD AGREEMENT REGARDING TC
INTENSITY.  A CROSS-TRACK SPREAD OF JUST 128NM BETWEEN JTWC
CONSENSUS MEMBERS CONTRIBUTES TO THE ASSESSMENT OF HIGH CONFIDENCE
IN TRACK THROUGHOUT THE FORECAST PERIOD. INTENSITY GUIDANCE
PRESENTS A NOTICEABLE AND UNIFORM DROP IN INTENSITY ACROSS THE JTWC
CONSENSUS SINCE THE PREVIOUS WARNING (162100Z). ADDITIONALLY, RAPID
INTENSIFICATION AIDS HAVE DECREASED PROBABILITY OF RI OCCURRENCE,
BUT STILL REMAIN NOTEWORTHY FROM TAU 00 TAO TAU 36 (BETWEEN 50 AND
80 PCT LIKELIHOOD OF RI OCCURRENCE). A 40KTS SPREAD IS OBSERVED
AMONG CONSENSUS MEMBERS BETWEEN TAU 24 AND 36, CONTRIBUTING TO
AN OVERALL INTENSITY FORECAST CONFIDENCE OF MEDIUM.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72 - 96 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72 - 96 HR: MEDIUM//
NNNN