WDPN31 PGTW 201500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SAUDEL) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 12.8N 150.2E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 314 NM EAST OF ANDERSEN AFB MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 18 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL STORM (TS) 17W IS NOW INTENSIFYING. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS EXPLOSIVE CENTRAL CONVECTION, WITH CLOUD TOP TEMPERATURES AS COLD AS -86 DEGREES CELSIUS, WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER. SURROUNDING THIS CORE CONVECTION, OUTER FEEDER BANDS ARE SHOWING INCREASING CURVATURE AND EXTENT. DESPITE THE PRESENCE OF MODERATE NORTHEASTERLY SHEAR IN THE 850-400 MB LAYER, THE UPPER-LEVEL OUTFLOW IS EXPANDING RADIALLY, INDICATING THAT THE SYSTEM IS SUCCESSFULLY OVERCOMING THE SHEAR. A FORTUITOUS 201101Z ASCAT-B PASS REVEALED UNFLAGGED 35-40 KT WINDS IN THE SOUTHEAST QUADRANT AND CONFIRMED A WIND FIELD THAT IS GRADUALLY BECOMING MORE SYMMETRIC. THE SURROUNDING ENVIRONMENT IS FAVORABLE FOR FURTHER DEVELOPMENT, CHARACTERIZED BY VERY WARM SEA SURFACE TEMPERATURES (SST) OF 30-31 DEGREES CELSIUS AND RICH, DEEP-LAYER MOISTURE. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE WELL-DEFINED CIRCULATION CENTER IN THE ASCAT-B PASS. THE INITIAL INTENSITY HAS BEEN RAISED TO 40 KTS, ALSO WITH HIGH CONFIDENCE, BASED ON THE SAME SCATTEROMETER DATA. PGTW, KNES, RJTD, AND RCTP HAVE PROVIDED SUBJECTIVE DVORAK FIXES OF T2.5, WHILE THE OBJECTIVE ESTIMATES FROM CIMSS LAG SLIGHTLY BEHIND. INITIAL WIND RADII BASIS: SCATTEROMETER DATA CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A LOW- TO MID-LEVEL RIDGE CENTERED AT 43N 173E AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.5 - 35 KTS RCTP: T2.5 - 35 KTS KNES: T2.5 - 35 KTS CIMSS SATCON: 39 KTS AT 200540Z CIMSS ADT: 32 KTS AT 201210Z CIMSS AIDT: 32 KTS AT 201210Z CIMSS D-MINT: 31 KTS AT 200720Z CIMSS D-PRINT: 41 KTS AT 201140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE VWS: 15-20 KTS SST: 29-30 CELSIUS OUTFLOW: MODERATE RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 17W IS NOW MOVING NORTHWESTWARD AT 11 KTS, A MOTION THAT WILL PERSIST FOR THE NEXT 36 HOURS UNDER THE STEERING INFLUENCE OF A RIDGE POSITIONED TO ITS NORTHEAST. AFTER TAU 36, A DEEP-LAYER RIDGE OVER THE CENTRAL NORTH PACIFIC WILL MIGRATE WESTWARD, INDUCING A MORE WESTWARD TRACK. COMPLICATIONS ARISING FROM THE INTERACTION OF A MONSOON DEPRESSION, DESIGNATED AS 94W, WITH THE SUBTROPICAL RIDGE (STR) OVER HONSHU RESULT IN SIGNIFICANT FORECAST TRACK UNCERTAINTY AT TAU 96 AND TAU 120. A SPECTRUM OF POSSIBLE TRACKS EXIST THAT DEPEND ON THE STRENGTH OF THE STR. ON ONE END OF THE SPECTRUM, THE MONSOON DEPRESSION REMAINS WEAK, ALLOWING FOR A STRONGER STR. THIS WOULD LEAD TO A ZONAL TRAJECTORY TOWARD THE SOUTHERN RYUKYU ISLANDS. THE OTHER END PRESENTS A STRONGER 94W, WHICH CREATES A WEAKNESS IN THE STR THAT WOULD ALLOW TS 17W TO TURN POLEWARD INTO SHIKOKU. THE JTWC FORECAST TRACK FAVORS THE FORMER SOLUTION AND DEPICTS A MORE ZONAL TRACK. THE CONVECTION ASSOCIATED WITH TS 17W IS EXPANDING RAPIDLY, AND THE SYSTEM IS ON THE PRECIPICE OF A PROLONGED PERIOD OF VERY RAPID INTENSIFICATION (RI). THE ENVIRONMENTAL CONDITIONS ONLY GET BETTER FROM THIS POINT FORWARD, WITH OCEAN HEAT CONTENT (OHC) INCREASING TO 125-150 KJ PER CM2 AND VERTICAL WIND SHEAR (VWS) DECREASING TO 5-10 KTS. ADDITIONALLY, AFTER TAU 12, THE SYSTEM WILL TAP INTO A POLEWARD OUTFLOW CHANNEL CREATED BY AN UPPER-LEVEL TROUGH. AS THE SYSTEM BECOMES MORE SYMMETRIC AND THE INNER CORE CONSOLIDATES, THESE FACTORS WILL FUEL VERY RAPID INTENSIFICATION TO A PEAK NEAR SUPER TYPHOON (STY) STATUS. THE SHIPS RI INDEX GIVES A 60 PERCENT PROBABILITY OF A 65 KT INCREASE IN WIND SPEED OVER THE NEXT 24 HOURS ALONE. ACHIEVING STY INTENSITY IS WELL WITHIN THE REALM OF POSSIBILITY, GIVEN THE HIGHLY FAVORABLE CONDITIONS AND A MAXIMUM POTENTIAL INTENSITY OF 135 KTS. AFTER PEAKING AROUND TAU 60-72, THE SYSTEM WILL ENTER A LESS FAVORABLE ENVIRONMENT OF HIGHER SHEAR AND LOWER OHC, LEADING TO SUBSEQUENT WEAKENING. EYEWALL REPLACEMENT CYCLES MAY ALSO BEGIN NEAR PEAK INTENSITY, WHICH WOULD INTRODUCE LESS PREDICTABLE FLUCTUATIONS IN INTENSITY AND AN EXPANDED WIND FIELD. MODEL DISCUSSION: WITH A CROSS-TRACK SPREAD OF LESS THAN 100 NM AT TAU 48, THE SHORT-TERM MODEL SOLUTIONS ARE IN GOOD AGREEMENT. HOWEVER, CONFIDENCE IN THE LONG-TERM FORECAST IS LOW, AS THE DIVERGENCE IN THE MODEL TRACKERS INCREASES TO 260 NM AT TAU 96 AND 430 NM AT TAU 120. THE SIGNIFICANT SPREAD IS DRIVEN BY TWO MODEL CAMPS. THE ECMWF AND THE AI MODEL SOLUTIONS HAVE SHIFTED EVEN FURTHER WESTWARD, BRINGING THE SYSTEM DIRECTLY OVER OR SOUTH OF OKINAWA BEYOND TAU 120. THE HAFS-A, GFS, NAVGEM, JGSM, AND GALWEM MODELS CONTINUE TO FAVOR A MORE POLEWARD TRACK TOWARD THE NORTHERN RYUKYU ISLANDS, KYUSHU, OR SHIKOKU. THE JTWC FORECAST TRACK IS POSITIONED NEAR THE JTWC CONSENSUS (CONW) THROUGH TAU 48 WITH HIGH CONFIDENCE. THEREAFTER, IT HEDGES CLOSER TO THE AI CONSENSUS WITH LOW CONFIDENCE. IT IS POSSIBLE THAT SUBSEQUENT FORECASTS WILL NEED TO SHIFT FURTHER SOUTHWARD IN THE LONG TERM IF THIS TREND CONTINUES. GIVEN THE RECENT IMPROVEMENTS IN THE SATELLITE PRESENTATION OF TS 17W, RAPID INTENSIFICATION IS IMMINENT, IF NOT ALREADY OCCURRING. THE INTENSITY FORECAST IS NOW MORE AGGRESSIVE, CALLING FOR A 75 KT INCREASE OVER THE NEXT 48 HOURS TO A PEAK OF 125 KTS. WHILE THIS FORECAST IS AT THE UPPER END OF THE INTENSITY GUIDANCE, COAMPS-TC IS EVEN MORE BULLISH WITH THE RATE OF INTENSIFICATION. THE EXPERIMENTAL GOOGLE DEEPMIND MODEL ALSO PEAKS AT 125 KTS, WITH NEARLY 40 PERCENT OF ITS ENSEMBLE MEMBERS ACHIEVING STY STATUS. THE HAFS-A SOLUTION PEAKS AT 130 KTS. REFLECTING THIS HIGH-END POTENTIAL, THE INTENSITY FORECAST HAS BEEN INCREASED OUT TO TAU 72. BEYOND THIS POINT, NEARLY ALL OF THE RELIABLE AIDS DEPICT A WEAKENING TREND, AND JTWC REFLECTS THIS. FORECAST CONFIDENCE: TRACK 00-72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 00-72 HR: MEDIUM INTENSITY 72-120 HR: MEDIUM// NNNN