WDPN31 PGTW 222100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) WARNING NR 002// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 11.8N 147.5E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 190 NM SOUTHEAST OF ANDERSEN AFB, GUAM MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS SIGNIFICANT WAVE HEIGHT: 11 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH BROAD AND DEEP FORMATIVE BANDS ALONG THE NORTHERN AND SOUTHERN PERIPHERIES. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE USING LOW CLOUD TRACING IN THE EIR LOOP AND EXTRAPOLATION FROM A 221443Z SCATTEROMETER BULLSEYE PASS. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW AND ADT DVORAK ESTIMATES AND ALSO SUPPORTED THE BY SCATTEROMETER PASS. 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: 29 KTS AT 221840Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE VWS: 0-5 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, MAKING LANDFALL OVER GUAM AROUND TAU 15. 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 78, THEN ACCELERATE NORTH- NORTHEASTWARD. THE FAVORABLE ENVIRONMENT WILL FUEL INTENSIFICATION TO 40-45KTS PRIOR TO LANDFALL OVER 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 130KTS BY TAU 120 AS INCREASED POLEWARD OUTFLOW IS ANTICIPATED IN CONJUNCTION WITH INITIAL EXPOSURE TO THE STRONG WESTERLIES AHEAD OF A MIDLATITUDE TROUGH. MODEL DISCUSSION: AVAILABLE NUMERICAL MODELS ARE IN VERY LOOSE AGREEMENT WITH THE GENERAL TRACK FORECAST WITH THE SPREAD REACHING 900+ NM BY TAU 120 MAINLY CAUSED BY UEMN 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 UEMN. THERE IS ALSO MEDIUM CONFIDENCE IN THE INTENSIRTY 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: MEDIUM// NNNN