WDPN31 PGTW 152100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (NOKAEN) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 10.2N 129.0E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 538 NM EAST-SOUTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 01 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION (TD) 01W (NOKAEN) WITH A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH STRUGGLING CENTRAL CONVECTION SHEARED THE WEST. THE VORTEX IS SHALLOW AND QUASI-STATIONARY. THE ENVIRONMENT IS MARGINALLY FAVORABLE, CHARACTERIZED BY STRONG UPPER-LEVEL DIFFLUENCE, WARM (28-29 C) SEA SURFACE TEMPERATURES, AND OFFSET BY HIGH (20-25 KTS) EASTERLY VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE FULLY EXPOSED LLCC. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: A DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.5 - 35 KTS KNES: T2.0 - 30 KTS CIMSS SATCON: 33 KTS AT 151709Z CIMSS ADT: 34 KTS AT 151730Z CIMSS AIDT: 31 KTS AT 151730Z CIMSS D-MINT: 29 KTS AT 151709Z CIMSS D-PRINT: 31 KTS AT 151830Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 20-25 KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD OTHER FACTORS: NORTHEASTERLY COLD SURGE TO THE NORTH OF THE STORM AND DRY AIR ENTRAINMENT ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH 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 01W WILL TRACK NORTHWESTWARD FOR THE NEXT 36 HOURS AS IT RIDES THE WESTERN PERIPHERY OF THE STEERING RIDGE CURRENTLY CENTERED TO THE NORTHEAST. AS IT TRACKS NORTHWESTWARD, NOKAEN WILL ENCOUNTER THE NORTHEASTERLY COLD SURGE AROUND TAU 48-72, INTRODUCING COOLER AND DRIER AIR. THE INTERACTION WILL SHALLOW THE VORTEX FURTHER, ALLOWING IT TO BE SUSCEPTIBLE TO LOWER-LEVEL STEERING INFLUENCES. 01W WILL BE MET WITH THE ADVANCING FRONTAL BOUNDARY ASSOCIATED WITH THE COLD SURGE BY TAU 72 AND PUSHED SOUTHWARD. THE SHALLOW NATURE OF THE VORTEX OPENS THE POSSIBILITY OF ERRATIC STORM MOVEMENT, ESPECIALLY AFTER ENCOUNTERING THE COLD SURGE. THE STORM IS EXPECTED TO TEETER AROUND TROPICAL STORM STRENGTH BETWEEN TAUS 12-72, WITH THE DRY AIR AND WIND SHEAR OFFSET BY A ROBUST POLEWARD OUTFLOW CHANNEL. BY TAU 48, HOWEVER, THE OUTFLOW CHANNEL IS LOST AND THE DRY AIR WILL SMOTHER THE SYSTEM, ULTIMATELY LEADING TO NOKAEN'S TERMINAL WEAKENING AND DISSIPATION BEYOND THE FORECAST PERIOD. MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT IN A NORTHWESTWARD TRACK FOR THE NEXT 48 HOURS, BUT VARIES THEREAFTER. UNCERTAINTY INCREASES WITHIN THE GUIDANCE DUE TO HOW THE MODELS INTERPRET THE SHALLOW VORTEX AND ITS INTERACTION WITH THE COLD SURGE. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS, GFS, AND ECMWF WITH MEDIUM CONFIDENCE FROM TAU 0-72 AND LOW CONFIDENCE FROM TAU 72-120. RELIABLE INTENSITY AIDS ARE IN MODERATE AGREEMENT IN A STAGNANT INTENSITY FOR THE MAJORITY OF THE FORECAST PERIOD, HOWEVER, MESOSCALE MODELS ARE INDICATING A SLIGHT INTENSIFICATION BEYOND 40 KTS. AS A RESULT, THE JTWC INTENSITY FORECAST IS ASSESSED WITH OVERALL MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN