WDXS31 PGTW 161500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 14S (DUDZAI) WARNING NR 
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 70.4E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 607 NM SOUTH-SOUTHWEST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 14S (DUDZAI) BEGINNING TO WEAKEN WITH A FILLED EYE AND AN
IRREGULAR CENTRAL DENSE OVERCAST (CDO). NORTHWESTERLY SHEAR HAS
STARTED TO MARKEDLY INCREASE, AND IS LIKELY THE CAUSE OF THE
WEAKENING. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON TRACKING THE FILLED EYE FEATURE IN ANIMATED MSI. THE
INITIAL INTENSITY OF 110 KTS IS ASSESSED WITH LOW CONFIDENCE BASED
PRIMARILY ON AGENCY DVORAK CURRENT INTENSITY (CI) NUMBERS RANGING
FROM T5.5-T6.5. COMMUNICATIONS ISSUES HAVE CAUSED CIMSS OBJECTIVE
INTENSITY ESTIMATES TO BE UNAVAILABLE FOR THE SYSTEM, FURTHER
ADDING TO THE UNCERTAINTY IN THE INITIAL INTENSITY. ENVIRONMENTAL
ANALYSIS INDICATES THAT 14S IS NOW IN A MARGINAL ENVIRONMENT
CHARACTERIZED BY STRONG POLEWARD OUTFLOW AND WARM (27-28 C) SEA
SURFACE TEMPERATURES GREATLY OFFSET BY MODERATE TO HIGH (20-25 KTS)
NORTHWESTERLY VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE NORTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   DEMS: T6.5 - 127 KTS
   FMEE: T5.5 - 102 KTS
   FIMP: T5.5 - 102 KTS
   CIMSS D-PRINT: 104 KTS AT 161200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 14S IS FORECAST TO IMMINENTLY TURN
SOUTHWESTWARD AS IT BEGINS TO TRACK ALONG THE NORTHWESTERN
PERIPHERY OF THE STR. A SOUTHWESTWARD TRACK IS FORECAST TO PERSIST
THROUGH TAU 96 AS IT CONTINUES TO ROUND THE RIDGE. NEAR TAU 96, THE
SYSTEM WILL HAVE REACHED THE RIDGE AXIS AND START A SOUTHEASTWARD
TURN AS IT TRACKS ALONG THE SOUTHWESTERN EXTENT OF THE RIDGE. TRACK
SPEEDS ARE ALSO EXPECTED TO INCREASE NEAR TAU 96 AS THE STEERING
GRADIENT INCREASES AND THE SYSTEM BEGINS TO INTERACT WITH THE
MIDLATITUDE WESTERLIES. REGARDING INTENSITY, 14S IS FORECAST TO
RAPIDLY WEAKEN THROUGH TAU 36 DUE TO THE HIGH NORTHWESTERLY SHEAR
AND COOLING SEA SURFACE TEMPERATURES. NEAR TAU 36, THE WEAKENING
TREND WILL CEASE DUE DECREASING SHEAR AND THE STRENGTHENING OF THE
POLEWARD OUTFLOW CHANNEL. THE WEAKENING TREND WILL THEN CONTINUE
AROUND TAU 96 AS WESTERLY SHEAR AND DRY AIR ENTRAINMENT BEGIN TO
INCREASE. 14S IS FORECAST TO BEGIN SUBTROPICAL TRANSITION AT TAU
120, WITH COMPLETION OF THE TRANSITION OCCURRING OUTSIDE OF THE
FORECAST WINDOW.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH NO SIGNIFICANT
OUTLIERS. CROSS-TRACK SPREAD AT TAU 72 IS 195 NM, WHICH OPENS UP TO
335 NM AT TAU 120. ALONG-TRACK SPREAD AT TAU 120 DOES INCREASE
QUITE A BIT AS THE SYSTEM ACCELERATES SOUTHEASTWARD. ALONG-TRACK
SPREAD AT TAU 120 IS AROUND 490 NM, AND IS THE PRIMARY CAUSE FOR
LOWERED CONFIDENCE IN THE JTWC TRACK AFTER TAU 72. THE JTWC TRACK
FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS THROUGHOUT
THE FORECAST PERIOD. INTENSITY GUIDANCE IS IN MODERATE AGREEMENT,
WITH MODELS GENERALLY AGREEING ON RAPID WEAKENING THROUGH TAU 36
AND A STEADY INTENSITY THROUGH TAU 120. THE JTWC INTENSITY FORECAST
IS ALSO PLACED NEAR THE CONSENSUS WITH MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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