WDPN31 PGTW 150900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (NOKAEN) WARNING NR 004// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 10.0N 128.9E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 539 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION 01W (NOKAEN) WITH A BROAD, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) AND DEEP CONVECTION CONFINED TO THE NORTHERN SEMICIRCLE. RELATIVELY DRIER AIR CAN BE SEEN WRAPPING INTO THE VORTEX FROM THE SOUTH, AND IS LIKELY THE CAUSE OF LITTLE TO NO CONVECTIVE ACTIVITY IN THE SOUTHERN SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON TRACING THE EXPOSED LOW-LEVEL CLOUDS IN ANIMATED MSI. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES THAT 01W IS IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT AND WARM (28-29 C) SEA SURFACE TEMPERATURES OFFSET BY MODERATE TO HIGH (20-25 KTS) EASTERLY VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: A DEEP-LAYER SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS KNES: T2.0 - 30 KTS CIMSS SATCON: 33 KTS AT 150435Z CIMSS ADT: 33 KTS AT 150530Z CIMSS AIDT: 33 KTS AT 150530Z CIMSS D-MINT: 26 KTS AT 150435Z CIMSS D-PRINT: 31 KTS AT 150630Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 20-25 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT FROM THE SOUTH 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: 01W IS FORECAST TO TRACK NORTHWESTWARD, ALONG THE WESTERN PERIPHERY OF THE STR TO THE NORTHEAST THROUGH TAU 48. NEAR TAU 48, ANOTHER STR CENTERED OVER THE SOUTH CHINA SEA WILL COMPETE FOR THE STEERING INFLUENCE OF 01W. THIS WILL CAUSE TRACK SPEEDS TO SLOW AS THE SYSTEM APPROACHES THE 15TH LATITUDE. NEAR TAU 72, 01W IS FORECAST TO BEGIN SLOWLY TRACKING EASTWARD, ALONG THE NORTHERN PERIPHERY OF THE STR TO THE EAST THROUGH TAU 120. THERE IS A POSSIBILITY THAT THE SYSTEM STALLS IN PLACE AROUND TAU 96 DUE TO THE COMPETING STEERING ENVIRONMENT. REGARDING INTENSITY, 01W IS FORECAST TO MARGINALLY INTENSIFY OVER THE NEXT 48 HOURS DUE PRIMARILY TO THE WARM SEA SURFACE TEMPERATURES AND ROBUST POLEWARD OUTFLOW. AFTER TAU 48, THE SYSTEM IS FORECAST TO GRADUALLY WEAKEN AS SOUTHERLY SHEAR AND DRY AIR ENTRAINMENT FROM THE SOUTH BOTH INCREASE. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 72 WITH THE EXCEPTION OF NAVGEM AND GALWEM, WHICH BOTH TRACK THE SYSTEM SIGNIFICANTLY FURTHER NORTH THAN THE REMAINDER OF GUIDANCE. DISCOUNTING THE TWO OUTLIERS, CROSS-TRACK SPREAD AT AU 72 IS AROUND 100 NM. AFTER TAU 72, UNCERTAINTY GREATLY INCREASES DUE TO DIFFERENCES IN HOW THE MODELS HANDLE THE VORTEX IN THE COMPETING STEERING ENVIRONMENT. GFS AND ECMWF BOTH STALL THE SYSTEM NORTH OF SAMAR WHILE THE AI MODELS SHOW THE SLOW EASTWARD MOVEMENT. THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 72 AND THEN MORE CLOSELY TO THE AI MODELS THEREAFTER. INTENSITY GUIDANCE IS IN GENERALLY GOOD AGREEMENT ON MARGINAL INTENSIFICATION THROUGH TAU 48 AND GRADUAL WEAKENING THROUGH TAU 120 WITH NO NOTABLE OUTLIERS. THE JTWC INTENSITY FORECAST IS PLACED CLOSE TO THE CONSENSUS THROUGHOUT THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN