WDPN31 PGTW 190300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) WARNING NR 003// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 8.0N 154.2E INITIAL INTENSITY: 30 KTS GEOGRAPHIC REFERENCE: 140 NM EAST-NORTHEAST OF CHUUK MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS SIGNIFICANT WAVE HEIGHT: 13 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL DEPRESSION (TD) 17W CONTINUING TO CONSOLIDATE WITH PERSISTENT CONVECTION OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). ENVIRONMENTAL ANALYSIS REVEALS MARGINALLY FAVORABLE CONDITIONS WITH WARM (30-31 C) SEA SURFACE TEMPERATURES (SSTS) AND STRONG RADIAL OUTFLOW ALOFT BEING OFFSET BY 10-15 KTS OF VERTICAL WIND SHEAR (VWS) AND AN AREA OF DRY AIR IN THE NORTHERN SEMICIRCLE, AS THE LOW LEVEL CLOUD LINES WRAPPING IN FROM THE NORTH REMAIN EXPOSED IN MSI. BOTH THE 89 GHZ AND 37 GHZ 182224Z GMI MICROWAVE IMAGES FURTHER ILLUSTRATE LOWER LEVEL CLOUD LINES WRAPPING INTO AN AREA SITUATED ON THE NORTHEASTERN PERIPHERY OF THE CONVECTION. ADDITIONALLY, AN 182300Z METOP-C ASCAT PASS DEPICTS AN ELONGATED LLCC AND A FIELD OF 25 KTS ON THE SOUTHERN SEMICIRCLE, WITH A SMALL AREA OF 30 KTS EMBEDDED WITHIN THE SOUTHEAST QUADRANT. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE MICROWAVE IMAGERY, ASCAT DATA, AND OBSCURED LLCC. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT DATA, AGENCY DVORAK FIXES, AND CIMSS OBJECTIVE ESTIMATES LISTED BELOW. INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND RADII). CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT COMPRISED OF NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTHEAST AND ELONGATED LOW-LEVEL TROUGH THAT 17W IS EMBEDDED WITHIN. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T1.5 - 25 KTS RJTD: T1.5 - 25 KTS KNES: T2.0 - 30 KTS CIMSS ADT: 32 KTS AT 180010Z CIMSS AIDT: 32 KTS AT 180010Z CIMSS D-MINT: 29 KTS AT 182221Z CIMSS D-PRINT: 25 KTS AT 190010Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 30-31 CELSIUS OUTFLOW: STRONG RADIAL OTHER FACTORS: AREA OF DRY AIR TO THE NORTH 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: TD 17W IS FORECAST TO TRACK GENERALLY NORTH-NORTHWESTWARD THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD. HOWEVER, AS THE VORTEX CONTINUES TO CONSOLIDATE IN THE SHORT-TERM, IT IS POSSIBLE FOR THE TRACK TO MAKE SMALL DEVIATIONS FROM THE OVERALL MEAN MOTION VECTOR. THE AREA OF HIGHEST WINDS LOCATED WITHIN THE SOUTHEASTERN QUADRANT ARE EXPECTED TO CONTINUE WRAPPING CYCLONICALLY, LIKELY CAUSING THE INDUCED SOUTHWESTWARD MOVEMENT. THE QUASI-STATIONARY MOVEMENT IS ALSO LIKELY DUE TO THE WEAK STEERING ENVIRONMENT OF 17W, AS THE SHALLOW SYSTEM IS EMBEDDED WITHIN AN ELONGATED TROUGH CAUSING WEAK WESTWARD MOTION, WHILE ALSO BEING INFLUENCED BY A NEAR-EQUATORIAL RIDGE (NER) CENTERED TO SOUTHEAST THAT IS EXPECTED TO BUILD AND CAUSE MORE POLEWARD MOTION BY TAU 12. AFTER THIS POINT, 17W IS EXPECTED TO CONTINUE MOVING POLEWARD TOWARDS A WEAKNESS IN STEERING AS THE EASTWARD EXTENSION OF A SUBTROPICAL RIDGE (STR) CENTERED OVER SOUTHERN JAPAN WEAKENS AND A WESTWARD EXTENSION OF AN STR CENTERED TO THE NORTHEAST BUILDS, ULTIMATELY CAUSING A WESTWARD TURN BETWEEN TAUS 60 AND 72, COINCIDING WITH THE TIME 17W IS FORECAST TO CROSS THE NORTHERN MARIANAS. REGARDING INTENSITY, TD 17W IS FORECAST TO STEADILY INTENSIFY AT ROUGHLY THE CLIMATOLOGICAL RATE TO TAU 36 AS IT GRADUALLY MOVES INTO BETTER ENVIRONMENTAL CONDITIONS OF LOWER VWS AND ENHANCED OUTFLOW ALOFT, WHILE UNDERGOING VORTEX SYMMETRIZATION. RAPID INTENSIFICATION (RI) IS FORECAST TO OCCUR FROM TAU 36 TO 72, WITH INTENSITY INCREASING AT LEAST 55 KTS DURING THIS TIME. AFTER CROSSING THE NORTHERN MARIANAS ISLAND CHAIN, 17W IS EXPECTED TO INTENSIFY MORE GRADUALLY AND THEN PLATEAU JUST BELOW SUPER TYPHOON THRESHOLD BY THE END OF THE FORECAST PERIOD. MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE OVERALL NORTH-NORTHWESTWARD TRACK FOR THE ENTIRETY OF THE FORECAST PERIOD. THE JGSM AND ECMWF DETERMINISTIC TRACKS ARE OUTLIERS TO THE EAST, PREDICTING A NORTHEASTWARD TRACK OUT TO TAU 12 BEFORE TURNING TO TRACK NORTHWESTWARD. ENSEMBLE MEMBERS DEPICT HIGHER CROSS TRACK SPREAD THAN THE DETERMINISTIC OR ENSEMBLE MEAN TRACKERS, WITH ECENS, ECAIE, AND GEFS ALL CONTAINING MEMBERS THAT TAKE 17W AS FAR SOUTH AS ROTA. THE OFFICIAL JTWC FORECAST TRACK IS PLACED WITH MEDIUM CONFIDENCE FOR THE FORECAST PERIOD IN BETWEEN THE MULTI-MODEL CONSENSUS AND EXPERIMENTAL GOOGLE DEEPMIND, WITH SOME UNCERTAINTY DUE TO THE POSITION OF THE CONSOLIDATING LLCC AFFECTING MODEL TRACKS IN THE LONG TERM OUT TO WHEN 17W IS EXPECTED TO PASS OVER THE MARIANAS. MODEL INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON THE SHORT-TERM GRADUAL INTENSIFICATION AND SUBSEQUENT PERIOD OF RI BEGINNING BY TAU 36. THE OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH CONFIDENCE OUT TO TAU 72 CLOSELY IN LINE WITH THE MULTI-MODEL CONSENSUS AND MEDIUM CONFIDENCE THEREAFTER, DEVIATING ABOVE THE CONSENSUS. FORECAST CONFIDENCE: TRACK 00-72 HR: MEDIUM TRACK 72-120 HR: MEDIUM INTENSITY 00-72 HR: HIGH INTENSITY 72-120 HR: MEDIUM// NNNN