WDPN31 PGTW 200900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 008// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 11.9N 150.9E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 367 NM EAST-SOUTHEAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 06 KTS SIGNIFICANT WAVE HEIGHT: 16 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH IS PARTIALLY OBSCURED BY PERSISTENT DEEP CONVECTION ALONG THE SOUTHERN PERIPHERY. MORE RECENTLY, NEW CONVECTION HAS FLARED UP OVER THE NE QUADRANT, A SIGN THAT THE SYSTEM WILL BEGIN TO BECOME MORE SYMMETRIC. TROPICAL STORM (TS) 17W HAS BEEN STRUGGLING TO INTENSIFY LARGELY DUE TO ITS HIGHLY ASYMMETRIC STRUCTURE AND THE PRESENCE OF LIGHT TO MODERATE NORTHEASTERLY MID-LEVEL SHEAR. A 200348Z AMSR2 37 GHZ IMAGE CONFIRMS THIS POOR ORGANIZATION, REVEALING A LACK OF AN INNER CORE AND DISORGANIZED CONVECTIVE BANDING. THE ENVIRONMENT IS FAVORABLE FOR DEVELOPMENT, CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES (SST) OF 29-30 DEGREES CELSIUS AND EXPANDING UPPER-LEVEL OUTFLOW. THESE FACTORS ARE OFFSET BY THE MODEST VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE PARTLY EXPOSED LLCC VISIBLE IN THE MSI. REFLECTING THE SYSTEM'S CONTINUED POOR ORGANIZATION, THE INITIAL INTENSITY IS HELD AT 35 KTS WITH MEDIUM CONFIDENCE, WHICH ALIGNS WITH THE T2.5 SUBJECTIVE DVORAK FIXES FROM PGTW AND RJTD AND IS CONSISTENT WITH THE OBJECTIVE ESTIMATES FROM CIMSS RANGING FROM 30 KTS TO 39 KTS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A LOW- TO MID-LEVEL RIDGE CENTERED AT 35N 172E AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.5 - 35 KTS RCTP: T2.0 - 30 KTS KNES: T2.0 - 30 KTS CIMSS SATCON: 39 KTS AT 200540Z CIMSS ADT: 33 KTS AT 200610Z CIMSS AIDT: 35 KTS AT 200610Z CIMSS D-MINT: 30 KTS AT 200330Z CIMSS D-PRINT: 30 KTS AT 200540Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE EASTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: AFTER A WESTWARD JOG BETWEEN 191800Z AND 200000Z, TS 17W HAS RESUMED A NORTHWESTWARD TRAJECTORY ALONG THE SOUTHWESTERN PERIPHERY OF A LOW- TO MID-LEVEL RIDGE TO ITS NORTHEAST. THIS WESTWARD SHIFT HAS BROUGHT THE GALE-FORCE WIND RADII CLOSER TO SAIPAN AND TINIAN. A DEEP-LAYER RIDGE, ALSO CENTERED TO THE NORTHEAST, WILL BECOME THE DOMINANT STEERING INFLUENCE AFTER TAU 24 AS THE STORM MATURES. THIS RIDGE WILL THEN BEGIN TO SHIFT WESTWARD BY TAU 48, FORCING THE STORM ONTO A MORE WEST-NORTHWESTWARD TRACK. SIGNIFICANT FORECAST UNCERTAINTY ARISES DUE TO POTENTIAL INTERACTION WITH A MONSOON DEPRESSION, DESIGNATED AS 94W, IN THE EXTENDED PERIOD. IN ONE SCENARIO, 94W SIGNIFICANTLY WEAKENS THE SUBTROPICAL RIDGE (STR) OVER SOUTHERN HONSHU, ALLOWING TS 17W TO CURVE POLEWARD BY TAU 120. IF THE STR REMAINS INTACT, THEN THE SYSTEM WILL CONTINUE ITS NORTHWESTWARD TRAJECTORY TOWARD THE RYUKYU ISLANDS. THE LATTER SCENARIO IS FAVORED BY THE JTWC FORECAST. THE SYSTEM IS BEGINNING TO SHOW SIGNS OF ORGANIZATION, WITH NEW CONVECTION FIRING UP AND WRAPPING INTO THE LLCC. THE ENVIRONMENT AHEAD WILL BE HIGHLY FAVORABLE FOR INTENSIFICATION. WITHIN THE NEXT 12 HOURS, THE VWS WILL EASE TO BELOW 10 KTS. CONCURRENTLY, THE SYSTEM WILL TRAVERSE OVER INCREASING LEVELS OF HIGH OCEAN HEAT CONTENT (OHC) AND BEGIN TO TAP INTO A POLEWARD OUTFLOW CHANNEL INDUCED BY AN UPPER-LEVEL TROUGH. THESE FACTORS WILL SUPPORT STEADY DEVELOPMENT IN THE NEAR TERM AS THE CIRCULATION UNDERGOES AXISYMMETERIZATION, FOLLOWED BY A PERIOD OF RAPID INTENSIFICATION AFTER TAU 12 TO A PEAK OF 120 KTS AT TAU 72. IN THE EXTENDED PERIOD, AS THE STORM APPROACHES THE LARGE CIRCULATION OF 94W, IT WILL ENCOUNTER INCREASING NORTHWESTERLY VWS. THIS, COMBINED WITH LOWER OHC, WILL LEAD TO STEADY WEAKENING TOWARD TAU 120. TO FURTHER COMPLICATE THE INTENSITY OUTLOOK, AS THE SYSTEM APPROACHES PEAK INTENSITY, IT MAY UNDERGO EYEWALL REPLACEMENT CYCLES (ERC), WHICH WOULD INTRODUCE LESS PREDICTABLE FLUCTUATIONS IN STRENGTH AND LEAD TO AN EXPANDED WIND FIELD. MODEL DISCUSSION: MODELS ARE IN TIGHT AGREEMENT FOR THE FIRST HALF OF THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF 60 NM AT TAU 48. HOWEVER, THE FORECAST CONFIDENCE PLUMMETS IN THE EXTENDED PERIOD, WITH A CROSS-TRACK SPREAD THAT INCREASES TO 250 NM AT TAU 96 AND 470 NM AT TAU 120. THIS LARGE DIVERGENCE IS DRIVEN BY TWO DISTINCT MODEL CAMPS. THE ECMWF AND AI MODELS FAVOR A MORE ZONAL TRACK TOWARD THE RYUKYU ISLANDS, WHILE THE HAFS-A, GFS, JGSM, NAVGEM, AND GALWEM MODELS LEAN TOWARD A MORE POLEWARD SOLUTION. NOTABLY, UNCERTAINTY ENVELOPE COVERS THE AREA FROM OKINAWA TO SHIKOKU. THE JTWC FORECAST TRACK HAS CHANGED LITTLE FROM 06 HOURS AGO, POSITIONED NEAR THE JTWC MULTI-MODEL CONSENSUS (CONW) FOR THE FIRST 48 HOURS AND NEAR THE AI CONSENSUS THEREAFTER. VIRTUALLY ALL INTENSITY AIDS SHOW SIGNIFICANT INTENSIFICATION. IN FACT, THE SHIP RI INDEX GIVES A 57 PERCENT PROBABILITY OF A 65 KT INCREASE IN WIND SPEED OVER THE NEXT 72 HOURS. THE JTWC INTENSITY FORECAST IS ALIGNED CLOSELY WITH THE EXPERIMENTAL GOOGLE DEEPMIND SOLUTION, PLACING IT ON THE UPPER END OF THE GUIDANCE ENVELOPE. MOST OF THE RELIABLE AIDS DEPICT WEAKENING BEGINNING AFTER TAU 72, A TREND THAT IS REFLECTED IN THE JTWC FORECAST. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN