WDPN33 PGTW 200900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (NESAT) WARNING NR 023// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.7N 108.2E INITIAL INTENSITY: 25 KTS GEOGRAPHIC REFERENCE: 102 NM NORTH OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 12 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH A BROAD FIELD OF STABLE STRATOCUMULUS CLOUDS PRESENT TO THE NORTHWEST ALONG THE COAST OF VIETNAM AND MORE UNSTABLE, BUT STILL LOW-LEVEL CUMULUS CLOUD LINES TO THE EAST. THE SYSTEM IS SHALLOW ENOUGH THAT IT IS NOT EVEN REFLECTED IN THE MOST RECENT LOW RESOLUTION ATMS MICROWAVE IMAGERY. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC AND AGENCY FIX POSITIONS. THE INITIAL INTENSITY IS ASSESSED AT 25 KNOTS WITH HIGH CONFIDENCE BASED ON THE AGENCY FIX TRENDS, WITH ONLY RJTD CONTINUING TO PROVIDE AN INTENSITY ESTIMATE AS WELL AS A PARTIAL 200214Z ASCAT-B PASS SHOWING MAXIMUM WINDS OF 25 KNOTS TO THE NORTHWEST AND PINNED ALONG THE COAST OF VIETNAM TO THE WEST. ANALYSIS REVEALS AN UNFAVORABLE ENVIRONMENT WITH MODERATE SOUTHEASTERLY VWS, SIGNIFICANT DRY AND STABLE AIR ENTRAINMENT OFFSET BY WARM SSTS AND MODERATE POLEWARD OUTFLOW. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: LOW TO MID-LEVEL FLOW ON THE SOUTHERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: NO CURRENT ESTIMATE RJTD: T1.5 - 25 KTS CIMSS ADT: 25 KTS AT 200230Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 15-20 KTS SST: 26-27 CELSIUS OUTFLOW: MODERATE POLEWARD 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: NOW THAT TD 23W HAS WEAKENED TO 25 KNOTS, THE ENTIRETY OF THE CIRCULATION IS CONSTRAINED BELOW THE 700MB LEVEL AND THE STEERING LEVEL HAS COME DOWN COMMENSURATELY. THE DEEP-LAYER MEAN FLOW IS FROM THE SOUTHEAST, BUT THE LOW-LEVEL 850MB FLOW THAT IS STEERING THE SYSTEM IS FROM THE EAST OVER THE GULF OF TONKIN AND IS FORECAST TO TURN MORE NORTHEASTERLY OVER THE NEXT 24 HOURS. THUS TD 23W, HAVING MOVED NORTHWESTWARD OVER THE PAST DAY IS ALREADY STARTING TO TURN MORE WESTWARD AND WILL OVER THE NEXT 24 TO 36 HOURS, TRACK IN A COUNTER-CLOCKWISE MOTION, ULTIMATELY MAKING LANDFALL NORTH OF HUE AROUND TAU 36. THE SYSTEM IS NOT EXPECTED TO INTENSIFY, BUT WILL LIKELY MAINTAIN 25 KNOT INTENSITY THROUGH LANDFALL AS IT SLOWLY SPINS DOWN, ESPECIALLY CONSIDERING THE ENHANCED GRADIENT FLOW PINNED ALONG THE VIETNAMESE COASTLINE. HOWEVER, IT IS POSSIBLE THE SYSTEM COULD WEAKEN BELOW 25 KNOTS AND DISSIPATE OVER WATER PRIOR TO LANDFALL. MODEL DISCUSSION: DUE TO THE VERY WEAK NATURE OF THE SYSTEM, TRACK GUIDANCE IS STRUGGLING, WITH A LARGE SPREAD IN THE TRACKERS. SOME INCLUDING THE JGSM, UKMET AND NAVGEM LOSE THE VORTEX WITHIN 12 HOURS, WHILE OTHERS INCLUDING GFS AND HWRF CONTINUE TRACKING A VORTEX FOR MORE THAN 72 HOURS. THE JTWC FORECAST IS BASED ON A BLEND OF PERSISTENCE WITH EARLIER FORECASTS, MODIFIED TO REFLECT THE GFS AND GALWEM TRACK SOLUTIONS. INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH A STEADY INTENSITY THROUGH AT LEAST TAU 12, FOLLOWED BY WEAKENING THEREAFTER. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH// NNNN