WDXS32 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (DINGANI) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.3S 83.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 854 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY
COMPACT SYSTEM WITH A PARTIALLY EXPOSED LOW LEVEL CIRCULATION
CENTER (LLCC) DISPLACED TO THE EAST OF A SMALL REGION OF FLARING
CONVECTION. TC 13S (DINGANI) CONTINUES TO STRUGGLE AGAINST
PERSISTENT EASTERLY SHEAR BUT HAS BEEN ABLE TO STEADILY INTENSIFY
OVER THE PAST 12 HOURS. UNFORTUNATELY, THERE HAS NOT BEEN ANY GOOD
MICROWAVE PASSES IN OVER 12 HOURS, AND THE SYSTEM IS CROSSING
THROUGH A REGION ON THE LIMBS OF BOTH HIMAWARI AND METEOSAT
GEOSTATIONARY IMAGERY, AND THUS THE INITIAL POSITION IS ASSESSED
WITH MEDIUM CONFIDENCE, USING AN EXTRAPOLATION OF AN 100324Z
ASCAT-B SCATTEROMETER PASS. THE INITIAL INTENSITY IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE T3.0 (45 KTS) CURRENT INTENSITY
ESTIMATES FROM PGTW AND DEMS, THE WIND FIELD EVIDENT IN THE
PREVIOUSLY MENTIONED ASCAT PASS AND THE CURRENT SATCON ESTIMATE.
SHEAR REMAINS IN THE LOW TO MODERATE RANGE (15-20 KTS) BUT HAS
STARTED TO COME DOWN SINCE THE PREVIOUS FORECAST. THE ENVIRONMENT
IS ASSESSED AS MARGINALLY FAVORABLE, WITH THE SHEAR BEING OFFSET BY
GOOD AND IMPROVING POLEWARD OUTFLOW AND WARM SSTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T2.5 - 35 KTS
   DEMS: T3.0 - 45 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS SATCON: 45 KTS AT 100210Z
   CIMSS ADT: 39 KTS AT 100600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: THROUGH THE FIRST 36 HOURS OF THE FORECAST, TC
13S IS FORECAST TO TRACK GENERALLY WESTWARD ALONG THE NORTHERN
PERIPHERY OF THE DEEP STR TO THE SOUTH. BY TAU 48, AN UPPER-LEVEL
TROUGH MOVING IN FROM THE WEST WILL BREAK DOWN THE RIDGE AND PUSH
THE CENTER TO THE EAST, RESULTING IN A MORE NORTH-SOUTH ORIENTED
AXIS. TC 13S WILL TAKE A SHARP TURN SOUTHWESTWARD ALONG THE NEWLY
REORIENTED RIDGE AXIS. A NEWLY FORMED STR WILL MOVE IN TO THE SOUTH
BY TAU 96, AND THE FORECAST TRACK FLATTENS SOMEWHAT THROUGH THE
REMAINDER OF THE FORECAST. SHEAR HAS ALREADY STARTED TO SLACKEN A
BIT BASED ON THE LATEST CIMSS ANALYSIS, SUPPORTED BY THE
REFORMATION OF A SMALL CENTRAL DENSE OVERCAST (CDO) OVER THE LLCC.
HOWEVER, IT WILL LIKELY TAKE A BIT OF TIME FOR THE INTENSITY TO
INCREASE SIGNIFICANTLY, THUS THE FORECAST CALLS FOR A FLAT INTENSITY
TREND FOR THE FIRST 12 HOURS. BY TAU 24, SHEAR IS EXPECTED TO RELAX
FURTHER, AND THE SYSTEM SHOULD START TO INTENSIFY MORE QUICKLY,
REACHING A PEAK OF 65 KNOTS BY TAU 48. INCREASED NORTHWESTERLY
SHEAR AHEAD OF THE DEEP TROUGH MOVING IN FROM THE WEST, AN INFLUX
OF DRY MID-LEVEL AIR, AND REDUCED SSTS (NEAR 26C) WILL USHER IN A
WEAKENING TREND FORM TAU 72 ONWARD. 

MODEL DISCUSSION: THROUGH TAU 48, DETERMINISTIC TRACK GUIDANCE IS
IN GOOD AGREEMENT, DEPICTING MINIMAL SPREAD IN THE CONSENSUS
MEMBERS, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK, WHICH
CLOSELY FOLLOWS THE CONSENSUS MEAN. AFTER TAU 72, THE DETERMINISTIC
TRACKERS BEGIN TO DIVERGE, THOUGH EVEN BY TAU 120 THE SPREAD IS A
MARGINAL 200NM. THE US MODELS INCLUDING NAVGEM, HWRF, AND GFS TAKE
THE SYSTEM ON A MORE SOUTHERLY ROUTE, WHILE THE EUROPEAN MODELS
INCLUDING UKMET, GALWEM, ECMWF AND THE THEIR ENSEMBLE MEAN
TRACKERS, TAKE A MORE NORTHERN TRACK. THE ENSEMBLES (GEFS, ECENS,
MOGREPS) SHOW SIGNIFICANTLY MORE SPREAD IN THE MEMBERS AFTER TAU
72, WITH SPREAD BETWEEN OUTLIE MEMBERS UP TO 600NM. THE JTWC
FORECAST LIES ON THE SOUTHERN SIDE OF THE CONSENSUS PACKAGE WITH
LOW CONFIDENCE, ESPECIALLY IN LIGHT OF THE INCREASED ENSEMBLE
SPREAD. INTENSITY GUIDANCE GENERALLY SUPPORTS THE FORECAST SCENARIO,
WITH A RANGE OF PEAK INTENSITIES BETWEEN 55 KNOTS FOR THE COAMPS-TC
(GFS) AND 75 KNOTS FOR THE HWRF. THE JTWC FORECAST LIES NEAR THE
CONSENSUS PEAK, WITH MEDIUM CONFIDENCE. 

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