WDPN31 PGTW 190900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (NOKAEN) WARNING NR 019// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.7N 126.6E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 347 NM EAST-NORTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 01 KTS SIGNIFICANT WAVE HEIGHT: 17 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL STORM (TS) 01W (NOKAEN) WITH PERSISTENT FLARING CONVECTION PARTIALLY OBSCURING THE LOW-LEVEL CIRCULATION CENTER (LLCC) WITH AN ASSOCIATED CONVECTIVE BAND EXTENDING WESTWARD THROUGH THE NORTHERN SEMICIRCLE. VERY DRY AIR HAS REMAINED EVIDENT SINCE THE PREVIOUS WARNING, PRIMARILY THROUGHOUT THE WESTERN AND SOUTHERN QUADRANTS, RESULTING LIMITED CONVECTION THROUGHOUT THE ENTIRE WESTERN SEMICIRCLE. ALOFT, UPPER-LEVEL OUTFLOW HAS BECOME RELATIVELY WEAK OVER THE LAST FEW HOURS, WITH A FRAGMENTED NORTHEASTWARD CHANNEL. THE ENVIRONMENT HAS REMAINED MARGINALLY FAVORABLE, WITH WARM SEA SURFACE TEMPERATURES (SST) OF 26-27 C, LOW VERTICAL WIND SHEAR (VWS) BELOW 15 KTS, AND THE AFOREMENTIONED PRESENCE OF LARGE SWATHS OF DRY AIR ENCIRCLING TS 01W. THE INITIAL POSITION HAS BEEN PLACED WITH HIGH CONFIDENCE, BASED ON THE OBSERVABLE PARTIALLY OBSCURED LLCC ON ANIMATED MSI. THE INITIAL INTENSITY HAS BEEN ASSESSED WITH MEDIUM CONFIDENCE BASED ON AGENCY SUBJECTIVE INTENSITY ESTIMATES RANGING FROM 25-35 KTS, AND CIMSS OBJECTIVE INTENSITY ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS RJTD: T1.5 - 25 KTS RCTP: T1.5 - 25 KTS KNES: T2.5 - 35 KTS CIMSS SATCON: 35 KTS AT 190501Z CIMSS ADT: 41 KTS AT 190530Z CIMSS AIDT: 38 KTS AT 190530Z CIMSS D-MINT: 26 KTS AT 190511Z CIMSS D-PRINT: 28 KTS AT 190630Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 26-27 CELSIUS OUTFLOW: WEAK POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 01W IS FORECASTED TO CONTINUE NORTHEASTWARD OVER THE NEXT 24 HOURS, ALONG THE NORTHWESTERN EXTENT OF THE STR LOCATED DIRECTLY TO THE EAST AND SOUTHEAST. FOLLOWING TAU 24, THE STR CENTERED OVER CAMBODIA AND VIETNAM WILL CONTINUE BUILDING WESTWARD, BECOMING THE PRIMARY STEERING DRIVER FOR TS 01W. WHEN THIS OCCURS, THE TRACK FOR TS NOKAEN WILL BECOME LARGELY SOUTHWARD BETWEEN TAU 36 AND TAU 72 ALONG THE EASTERN PERIPHERY OF THE STR NOW CENTERED DIRECTLY TO THE WEST. REGARDING INTENSITY, SLIGHT INTENSIFICATION IS FORECASTED OVER THE NEXT 12 HOURS, AS TS 01W ATTEMPTS TO MAINTAIN A MOIST CORE IN AN INCREASINGLY DRY ENVIRONMENT. BETWEEN TAU 12 AND TAU 24, VWS IS FORECASTED TO INCREASE TO MORE THAN 20 KTS, INITIATING A GRADUAL WEAKENING TREND. FOLLOWING TAU 36, DRY AIR AND PERSISTENT UNFAVORABLE VWS GREATER THAN 25 KTS WILL ERODE THE SYSTEMS CENTRAL VORTEX, EXACERBATING THE TERMINAL WEAKENING PHASE TOWARD 25 KTS BY TAU 72. BY TAU 72, TS 01W IS FORECASTED TO DISSIPATE AS A SIGNIFICANT TROPICAL CYCLONE OVER WATER, FROM OVERWHELMING NON-CONDUCIVE ENVIRONMENTAL INFLUENCES, INCLUDING VWS OVER 30 KTS, INCREASING DRY AIR, AND LIMITED OUTFLOW ALOFT. MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE CONTINUES IN FAIR AGREEMENT THROUGH THE INITIAL 12 HOURS OF THE FORECAST PERIOD, WITH AN ASSOCIATED 37 NM CROSS-TRACK SPREAD. FOLLOWING TAU 12, JTWC CONSENSUS MEMBERS BEGIN TO DIVERGE SIGNIFICANTLY DURING THE EXPECTED APPROACH TOWARD THE RE-CURVE TRACK SOUTHWARD. THE CROSS-TRACK SPREAD INCREASES TO 96 NM BY TAU 24, AND EVENTUALLY TOWARD 451 NM BY THE END OF THE FORECAST PERIOD. ALTHOUGH THE MAJORITY OF JTWC CONSENSUS SOLUTIONS ILLUSTRATE A SOUTHWARD TURN FOLLOWING TAU 24, NAVGEM CONTINUES TO CHARACTERIZE THE TIGHTER RECURVE SOLUTION, HOLDING THE WESTERN MOST TRACK, WHILE THE ECMWF ENSEMBLE MEAN EXPECTS A COMPLETE DISSIPATION FARTHER NORTHWARD. THEREFORE, THE JTWC TRACK FORECAST HAS BEEN PLACED WITH LOW CONFIDENCE THROUGHOUT THE 72 FORECAST PERIOD DUE TO THE INCREASING CROSS-TRACK SPREAD NEAR DISSIPATION. REGARDING INTENSITY, ALL AVAILABLE INTENSITY MEMBERS SHOW A STEADY OR SLIGHT INTENSIFICATION PHASE OVER THE NEXT 24 HOURS, WITH GRADUAL WEAKENING THEREAFTER. DUE TO THE TIMING OF DISSIPATION NEAR TAU 72, THE JTWC INTENSITY FORECAST WAS ASSESSED WITH MEDIUM CONFIDENCE. FORECAST CONFIDENCE: TRACK 00-72 HR: LOW INTENSITY 00-72 HR: MEDIUM// NNNN