WDXS31 PGTW 180900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 01S (ONE) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.8S 85.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 814 NM EAST-SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION, WITH FLARING, ISOLATED DEEP
CONVECTION SHEARED OVER THE SOUTHERN QUADRANT. A 180335Z ASCAT-B
IMAGE REVEALS A WEAKENING CIRCULATION, OPENING UP OVER THE NORTHERN
QUADRANT, WITH A SMALL AREA OF 30 KNOT VECTORS CONFINED TO THE
SOUTHERN QUADRANT. THE INITIAL INTENSITY IS HELD SLIGHTLY HIGHER THAN 
THE ASCAT VECTORS BASED ON THE HISTORICALLY LOW BIAS. THE INITIAL 
INTENSITY ASSESSMENT IS SUPPORTED BY THE PGTW CURRENT INTENSITY 
ESTIMATE OF 2.5 (35 KNOTS) AND THE RECENT CIMSS SATCON ESTIMATE. 
ENVIRONMENTAL CONDITIONS REMAIN MARGINAL, WITH MODERATE (20 KNOTS) 
MID-LEVEL VERTICAL WIND SHEAR (VWS) AND SIGNIFICANT MID-LEVEL DRY AIR 
ENTRAINMENT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW-LEVEL SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   FMEE: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 180345Z
   CIMSS ADT: 33 KTS AT 180615Z
   CIMSS AIDT: 30 KTS AT 180615Z
   CIMSS D-PRINT: 27 KTS AT 180545Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE 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: TROPICAL CYCLONE (TC) 01S IS EXPECTED TO TRACK
WEST-SOUTHWESTWARD THROUGH TAU 24 ALONG THE NORTHERN PERIPHERY OF
THE LOW-LEVEL STR. THE SYSTEM WILL CONTINUE TO WEAKEN DUE TO STEADY
MODERATE VWS AND INCREASING DRY AIR ENTRAINMENT. THE SYSTEM WILL
DISSIPATE BY TAU 24.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 24, WITH A 45-NM CROSS-TRACK SPREAD AT TAU 24. THE
ECENS AND GEFS ENSEMBLES SUPPORT THE JTWC TRACK AND INTENSITY
FORECAST WITH MEDIUM CONFIDENCE.  

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