WDPN31 PGTW 230900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.0N 144.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 19 NM SOUTH-SOUTHWEST OF HAGATNA, GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 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 CENTER (LLCC). THE 230348Z AMSR2
89GHZ MICROWAVE IMAGE SHOWS THE DEEPEST CONVECTION HAS REMAINED
REMOVED FROM THE LLCC. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE AFOREMENTIONED MSI AND MICROWAVE IMAGE. THE
INTENSITY IS SUPPORTED BY AUTOMATED AND AGENCY DVORAK FIXES. THE
ENVIRONMENT IS HIGHLY FAVORABLE WITH LOW VWS, AN UPPER LEVEL POINT
SOURCE NEARLY OVERHEAD, AND VERY WARM SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 36 KTS AT 230348Z
   CIMSS ADT: 33 KTS AT 230540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECAST TRACK HAS SHIFTED LEFT OF
THE PREVIOUS FORECAST WITH AN INCREASED TRACK SPEED.

FORECAST DISCUSSION: TS 20W WILL CONTINUE NORTHWEST THROUGH AN
INCREASINGLY FAVORABLE ENVIRONMENT OF WARM SEA SURFACE TEMPERATURES
(30-31 DEGREE CELSIUS), LOW SHEAR AND STRONG UPPER LEVEL OUTFLOW.
THE HIGHLY FAVORABLE ENVIRONMENT WILL FUEL SUSTAINED
INTENSIFICATION TO 125 KNOTS BY TAU 96. AFTERWARDS, TS 20W WILL BE
SLIGHTLY HAMPERED BY INCREASING VERTICAL WIND SHEAR. AROUND TAU
120, TS 20W WILL REACH THE STR AXIS BEFORE BEGINNING A GRADUAL
RECURVE SOUTHWEST OF JAPAN.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN SIGNIFICANT DISAGREEMENT
WITH GFS AND GFS ENSEMBLE SHOWING A NEAR POLEWARD TRACK, WHEREAS
THE REMAINING MODELS SHOW A MORE GRADUAL RECURVE WITH A SUSTAINED
NORTHWESTERLY TRACK THROUGH TAU 96. UKMET AND THE UKMET ENSEMBLE
TRACKS ARE FURTHER DELAYED IN THEIR RECURVE TIMING WITH SUBTROPICAL
RIDGE AXIS TO THE SOUTH OF KADENA. THE JTWC TRACK IS LAID ALONG THE
BULK OF THE GUIDANCE WITH A SUSTAINED NORTHWESTERLY TRACK. JTWC
INTENSITY GUIDANCE IS IN OVERALL AGREEMENT WITH RAPID
INTENSIFICATION EXPECTED BETWEEN TAU 12 AND TAU 36.

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