WDPN31 PGTW 210900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE) WARNING NR 007// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 20.3N 122.9E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 359 NM NORTH-NORTHEAST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS SIGNIFICANT WAVE HEIGHT: 15 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TD 25W CONTINUES TO SLOWLY CONSOLIDATE BUT HAS YET TO COMMENCE SIGNIFICANT INTENSIFICATION. ANALYSIS OF THE LOW-LEVEL CLOUD LINES EXPOSED TO THE EAST OF THE CENTRAL DENSE OVERCAST (CDO) SUGGESTS THE LOW LEVEL CIRCULATION CENTER (LLCC) IS ON THE EASTERN SIDE OF THE CDO WHICH EXTENDS WESTWARD INTO THE LUZON STRAIT. SURFACE WINDS AT BASCO AND ITBAYAT ARE FROM THE NORTH AT AROUND 16-20 KNOTS, INDICATING THE SURFACE CIRCULATION REMAINS TO THEIR EAST. 21523Z AMSR2 COLORIZED 89GHZ AND 36GHZ MICROWAVE IMAGERY IS NOT CLEAR-CUT BUT DOES SHOW SOME SHALLOW SPIRAL BANDS WRAPPING INTO AN OBSCURED LLCC, WITH DEEP CONVECTION TO THE WEST. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY REMAINS SET AT 30 KNOTS WITH HIGH CONFIDENCE, ON THE HIGHER END OF THE AGENCY DVORAK CURRENT INTENSITY ESTIMATES, BUT BELOW THE MAJORITY OF THE OBJECTIVE INTENSITY ESTIMATES. THE 210523Z AMSR2 WINDSPEED PRODUCT SHOWED A LOPSIDED WIND FIELD WITH LIGHT WINDS TO THE EAST AND 25-30 KNOT WINDS TO THE WEST, PROVIDING ADDITIONAL CONFIDENCE TO THE INITIAL INTENSITY. THE SYSTEM IS MOVING AT A FAIR CLIP TOWARDS THE WEST ALONG THE SOUTHERN SIDE OF A LARGE SUBTROPICAL RIDGE (STR). UPPER-LEVEL ANALYSIS REVEALS A WEAK, MESOSCALE ANTICYCLONE HAS DEVELOPED DIRECTLY OVER OR SLIGHTLY NORTHEAST OF THE SYSTEM, PROVIDING FOR LOW VWS BUT RELATIVELY WEAK UPPER-LEVEL OUTFLOW. SSTS ARE HIGH, BUT OHC IS LOW THROUGH THE LUZON STRAIT, OFFSETTING THE OTHERWISE FAVORABLE CONDITIONS. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER STR COMPLEX TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.0 - 25 KTS KNES: T2.0 - 30 KTS CIMSS SATCON: 42 KTS AT 210514Z CIMSS ADT: 33 KTS AT 210610Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 5-10 KTS SST: 28-29 CELSIUS OUTFLOW: WEAK POLEWARD AND EQUATORWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: THE SYSTEM IS EXPECTED TO CONTINUE TRACKING WEST OF THE NEXT 24 TO 36 HOURS AS THE RIDGE COMPLEX TO THE NORTH REMAINS FIRMLY ENTRENCHED. FORWARD SPEED WILL SLOW A BIT TOWARDS TAU 36 AS A BUILDING STR CENTERED OVER THE CHINA-VIETNAM BORDER WILL TAKE OVER AS THE PRIMARY STEERING INFLUENCE. BY TAU 48, TD 25W WILL BE ON A SOUTHWESTWARD TRAJECTORY THAT WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST. TD 25W CONTINUES TO CONSOLIDATE BUT AT A SLOW PACE. PRESSURES REMAIN FAIRLY HIGH AT BASCO AND ITBAYAT (AROUND 1010 MB), MEANING THAT TD 25W HAS AN EXTREMELY SMALL INNER CORE, AND IS THUS MORE SUSCEPTIBLE TO SMALL-SCALE INFLUENCES, SUCH AS ENTRAINMENT OF RELATIVELY STABLE AIR INTO THE WESTERN SIDE OF THE SYSTEM, WHICH WILL CONTINUE TO AFFECT THE INNER STRUCTURE FOR THE NEXT 12 HOURS OR SO. THUS INTENSIFICATION IS EXPECTED TO BE SLOW, AROUND 10 KNOTS PER DAY, DUE TO THE COMPETING AND OFFSETTING INFLUENCES OF LOW VWS, WEAK UPPER-LEVEL OUTFLOW AND ENTRAINMENT OF RELATIVELY MORE STABLE AIR IN THE WESTERN PERIPHERY. THE PEAK INTENSITY HAS BEEN LOWERED TO 50 KNOTS, EXPECTED TO BE REACHED BY TAU 48. THEREAFTER, CONVERGENT FLOW ALOFT CAUSED BY THE ASYMMETRIC POSITIONING OF THE 200MB ANTICYCLONE TO THE NORTH OF THE SYSTEM, COMBINED WITH A MODEST INCREASE IN EASTERLY SHEAR, WILL COMBINE TO SMOTHER THE SYSTEM AND LEAD TO RAPID WEAKENING AFTER TAU 72. BUT THE END OF THE FORECAST THE SYSTEM IS EXPECTED TO BE NEAR LANDFALL NEAR DA NANG, VIETNAM, AS A WEAK TROPICAL DEPRESSION. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN VERY GOOD AGREEMENT, PARTICULARLY THROUGH TAU 96. THE SOLE EXCEPTION IS THE GALWEM, WHICH TURNS THE SYSTEM NORTH AT TAU 24, MAKES LANDFALL OVER CENTRAL TAIWAN AND THEN PERFORMS A HIGHLY UNLIKELY CLOCKWISE LOOP ENDING AT THE SOUTHERN TIP OF TAIWAN BY TAU 120. THE REMAINDER OF THE CONSENSUS MEMBERS ARE ENCASED WITHIN A VERY SMALL ENVELOPE, WHICH GRADUALLY EXPANDS TO JUST 50NM AT TAU 72. SPREAD INCREASES TO 190NM AT TAU 120 AS THE SYSTEM RAPIDLY WEAKENS AND THE MODELS BEGIN TO LOSE LOCK ON THE VORTEX. THE GEFS AND ECENS ENSEMBLES ARE IN TIGHT AGREEMENT HOWEVER WITH THE DETERMINISTIC MEAN, AND THUS PROVIDE HIGH CONFIDENCE TO THE JTWC FORECAST TO TAU 72, AND MEDIUM CONFIDENCE THEREAFTER. INTENSITY GUIDANCE IN OVERALL BETTER AGREEMENT THAN THE PREVIOUS RUN, WITH ALL BUT THE COTC MODEL AGREEING ON A INTENSIFICATION TO 50 KNOTS FOLLOWED BY A FAIRLY RAPID WEAKENING THROUGH THE END OF THE FORECAST. THE HWRF INTERESTINGLY INCREASES THE INTENSITY TO 50 KNOTS BY TAU 12 THEN WEAKENS RAPIDLY THROUGH TAU 120 THOUGH THE OTHER MODELS PEAK BETWEEN TAU 36 AND TAU 48. THE JTWC FORECAST LIES AMONGST THE TIGHTEST GROUPING OF MODELS, JUST A SHADE ABOVE THE CONSENSUS MEAN WITH HIGH CONFIDENCE. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: MEDIUM INTENSITY 0 - 72 HR: HIGH INTENSITY 72-120 HR: HIGH// NNNN