WDXS31 PGTW 020300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01S (ANCHA) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 10.0S 75.7E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 258 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) AND EARLY MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS TROPICAL CYCLONE (TC) 01S (ANCHA) CONTINUING TO
IMPROVE STRUCTURALLY, WITH A SYMMETRICAL CENTRAL DENSE OVERCAST
DEVELOPING OVER THE PAST SIX HOURS OR SO. A 012205Z GMI PASS
REVEALED A NASCENT MICROWAVE EYE FEATURE IN THE 89GHZ BAND, WITH
STRONG CONVECTIVE BANDING MOSTLY LIMITED TO THE WESTERN SIDE OF THE
CENTER, WITH SHALLOW BANDING ON THE EASTERN SIDE. THE COLOR
ENHANCED 36GHZ IMAGE SHOWED A WELL-DEFINED MICROWAVE EYE FEATURE
WITH A LARGE BAND OF CONVECTION FAR TO THE EAST WRAPPING INTO THE
SMALL INNER CORE OF THE SYSTEM. THE INITIAL POSITION WAS ASSESSED
WITH HIGH CONFIDENCE USING AN EXTRAPOLATION OF THE MICROWAVE EYE
FEATURES DISCUSSED ABOVE AND AN ARCHER FIX FROM 020046Z. THERE IS A
LARGE SPREAD BETWEEN THE T2.0 (30 KTS) FROM KNES, UP TO THE T3.0
(45 KTS) FROM FMEE. THE CIMSS ADT OF T3.1 (47 KTS) AND THE DPRINT
ESTIMATE OF 43 KTS SEEM MORE CONSISTENT WITH THE OVERALL STRUCTURE
OF THE SYSTEM, HENCE THE INITIAL INTENSITY IS HEDGED TOWARDS THESE
VALUES, WITH MEDIUM CONFIDENCE. THE ENVIRONMENT REMAINS OVERALL
FAVORABLE WITH LOW DEEP-LAYER SHEAR, ROBUST POLEWARD OUTFLOW AND
WARM SST VALUES, HOWEVER THE CIMSS MID-LEVEL SHEAR ESTIMATE, AS
WELL AS MODEL SOUNDINGS SUGGEST A MODERATE AMOUNT OF EASTERLY SHEAR
IS LURKING UNDER THE HOOD, OFFSETTING THE OTHERWISE POSITIVE
ENVIRONMENT.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SCATTEROMETER
DATA. 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   FMEE: T3.0 - 45 KTS
   CIMSS ADT: 47 KTS AT 012330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MODERATE MID-LEVEL EASTERLY SHEAR. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 ANCHA WILL CONTINUE TO TRACK SOUTHWESTWARD 
ALONG THE NORTHWEST SIDE OF THE STR THROUGH THE ENTIRETY OF THE 
FORECAST PERIOD. A SLIGHT TURN MORE POLEWARD IS EXPECTED AT THE END OF 
THE FORECAST, AS THE SYSTEM BEGINS TO ROUND THE AXIS OF THE
STEERING RIDGE. AT THAT POINT THE SYSTEM WILL HAVE DISSIPATED AS A
TROPICAL CYCLONE, BUT THE REMNANT VORTEX IS LIKELY TO TURN SOUTHWARD 
AFTER THE END OF THE FORECAST. IN THE NEAR-TERM, THE ROBUST OUTFLOW 
AND RELATIVELY LOW DEEP-LAYER SHEAR WILL FUEL SOME ADDITIONAL 
INTENSIFICATION, UP TO 50 KNOTS BY TAU 12. THEREAFTER, MID-LEVEL SHEAR 
IS EXPECTED TO INCREASE FIRST, THEN DRY AIR WILL MOVE IN FROM THE 
WEST, WHICH WILL START TO WEAKENING TREND. BY TAU 36, DEEP LAYER SHEAR 
WILL INCREASE AND DRY AIR WILL COMPLETELY ENGULF THE VORTEX, 
COMMENCING A MORE RAPID WEAKENING PHASE. THE SYSTEM IS EXPECTED TO 
DISSIPATE BELOW WARNING CRITERIA NO LATER THAN TAU 72, AND LIKELY AS 
EARLY AS TAU 60. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE REMAINS
IN VERY GOOD AGREEMENT, WITH A MINIMAL SPREAD OF 150NM BY TAU 72.
THE GFS AND GEFS ENSEMBLE MEAN MARKS THE NORTHERN EDGE OF THE
ENVELOPE, WHILE THE ECMWF AND ECEPS MARK THE SOUTHERN. THE JTWC
FORECAST REMAINS CLOSE TO BUT JUST SOUTH OF THE MULTI-MODEL
CONSENSUS MEAN WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT, WITH THE BULK OF THE MEMBERS SHOWING A SMALL AMOUNT OF
INTENSIFICATION THROUGH TAU 12, FOLLOWED BY A STEADY WEAKENING
TREND THROUGH THE END OF THE FORECAST. 

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