WDPN31 PGTW 230300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.3N 146.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 106 NM SOUTHEAST OF ANDERSEN AFB, GUAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS
MAINTAINED OVERALL CONVECTIVE SIGNATURE AS THE LOW LEVEL CIRCULATION 
HAS BECOME MORE DEFINED. THE INITIAL POSITION AND INTENSITY ARE 
PLACED 
WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM A 222201Z 
SCETTEROMETRY BULLSEYE PASS AND SUPPORTED BY THE PGTW AND ADT DVORAK 
FIXES. THE ENVIRONMENT IS HIGHLY FAVORABLE WITH LOW VWS, STRONG 
POLEWARD AND EQUATORWARD OUTFLOW, AND VERY WARM SSTS. THE CYCLONE IS 
TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE STR TO THE NORTH.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A
DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 222040Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TD 20W WILL CONTINUE ON ITS CURRENT TRACK
UNDER THE STR, PASSING JUST TO THE SOUTH OF GUAM BEFORE TAU 12.
AFTER TAU 48, THE SYSTEM WILL TURN MORE POLEWARD AS IT BEGINS TO
ROUND THE WESTERN EDGE OF THE STR, CRESTING THE AXIS AROUND TAU 96,
THEN ACCELERATE NORTH-NORTHEASTWARD. THE FAVORABLE ENVIRONMENT WILL
FUEL INTENSIFICATION TO 45KTS AS IT PASSES BY GUAM, TEMPERED ONLY
BY SOME SUBSIDENCE ASSOCIATED WITH A TUTT TO THE NORTH. AFTER TAU
24, AS THE TUTT RECEDES, A MORE RAPID INTENSIFICATION IS EXPECTED,
REACHING 125KTS BY TAU 96 AS INCREASED POLEWARD OUTFLOW IS
ANTICIPATED IN CONJUNCTION WITH INITIAL EXPOSURE TO THE STRONG
WESTERLIES AHEAD OF A MIDLATITUDE TROUGH. AFTERWARD, INCREASING VWS
WILL BEGIN TO WEAKEN THE SYSTEM, DOWN TO 115KTS BY TAU 120. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN VERY LOOSE AGREEMENT WITH
THE GENERAL TRACK FORECAST WITH THE SPREAD REACHING 795 NM BY TAU
120 MAINLY CAUSED BY UEMN AND AFUM ON THE EXTREME LEFT MARGIN OF
THE MODEL ENVELOPE. IN VIEW OF THIS, THERE IS MEDIUM CONFIDENCE IN
THE JTWC TRACK FORECAST UP TO TAU 72 AND LOW CONFIDENCE AFTERWARD,
PROPORTIONALLY ADJUSTED TO THE RIGHT OF THE MODEL CONSENSUS TO
OFFSET THE LEFT OUTLIERS. THERE IS ALSO MEDIUM CONFIDENCE IN THE
INTENSITY FORECAST UP TO TAU 120.


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