Advisories

WDPN31 PGTW 212100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1N 147.3E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 143 NM NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
17W (SAUDEL) CONTINUING TO STRENGTHEN AS CONVECTIVE BANDING 
PREVIOUSLY STRONGEST ON THE EASTERN FLANK HAS WRAPPED AROUND THE 
NORTHERN SEMICIRCLE AND A BETTER-DEFINED BAND OF BURSTING CONVECTION 
HAS DEVELOPED ALONG THE WESTERN PERIPHERY. THIS SYMMETRIZATION AND 
APPEARANCE OF A NASCENT EYE IN EIR IMAGERY REFLECT ONGOING RAPID 
INTENSIFICATION (RI). TY 17W IS CURRENTLY IN HIGHLY FAVORABLE 
ENVIRONMENTAL CONDITIONS CHARACTERIZED BY LOW (5-10 KTS) VERTICAL 
WIND SHEAR (VWS), WARM (29-30 C) SEA SURFACE TEMPERATURES (SSTS), AND 
STRONG POLEWARD OUTFLOW ALOFT DUE TO AN UPPER LEVEL HIGH CENTERED TO 
THE NORTHEAST OF THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH 
HIGH CONFIDENCE BASED ON THE WELL-DEFINED WRAPPING IN EIR IMAGERY AND 
A TIGHT GROUPING OF AGENCY FIXES. THE INITIAL INTENSITY IS ASSESSED 
WITH HIGH CONFIDENCE, ABOVE THE MAJORITY OF AGENCY DVORAK FIXES AND
CIMSS OBJECTIVE ESTIMATES AS THE DVORAK-BASED INTENSITIES ARE
EXPECTED TO LAG DUE TO CONSTRAINTS DURING RI.

INITIAL WIND RADII BASIS: WIND RADII ADJUSTED BASED ON A 211105Z 
METOP-C ASCAT PASS, PERSISTENCE, AND OBJECTIVE BEST TRACK DATA

CURRENT STEERING MECHANISM: WESTWARD EXTENSION OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 71 KTS AT 211700Z
   CIMSS ADT: 59 KTS AT 211740Z
   CIMSS AIDT: 53 KTS AT 211740Z
   CIMSS D-MINT: 79 KTS AT 211538Z
   CIMSS D-PRINT: 81 KTS AT 211540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: TY 17W IS FORECAST TO TRACK NORTH-NORTHWESTWARD 
OUT TO TAU 24 UNDER THE STEERING INFLUENCE OF THE WESTWARD EXTENSION 
OF A SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. AFTER THIS 
POINT, THE EXTENSION IS EXPECTED TO BUILD WESTWARD AND CONNECT WITH 
AN STR CENTERED OVER KYUSHU, WHICH WILL DRIVE 17W ON A DIRECT 
NORTHWESTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD. THERE 
IS SOME UNCERTAINTY IN THE FORECAST TRACK BEGINNING AT TAU 96, AS GFS 
EXPECTS THE STR OVER KYUSHU TO FLATTEN AND MIGRATE INTO THE SEA OF 
JAPAN, CAUSING THE DOMINANT EASTERN STR TO STEER 17W NORTH OF 
OKINAWA. CONVERSELY, ECMWF DEPICTS A SOUTHWARD BUILDING OF THE STR 
OVER KYUSHU DUE TO THE EXPECTED DISSIPATION OF MONSOON DEPRESSION 94W 
TO THE SOUTH, RESULTING IN A WEST-SOUTHWESTWARD TURN OF 17W BETWEEN 
TAUS 96 AND 120. THE JTWC FORECAST HEDGES TOWARDS THE SECOND 
SCENARIO, BRINGING THE TRACK FARTHER SOUTH TOWARDS OKINAWA BY TAU 
120. REGARDLESS OF THE LONG-RANGE STEERING ENVIRONMENT, A SLOWDOWN IN 
TRACK SPEED AT THIS POINT OF THE FORECAST IS EXPECTED AS 17W NEARS 
THE AXIS OF THE EASTERN STR. REGARDING INTENSITY, TY 17W IS FORECAST 
TO CONTINUE RI THROUGHOUT TAU 24 AS IT WILL REMAIN IN HIGHLY 
FAVORABLE ENVIRONMENTAL CONDITIONS AND PEAK AT SUPER TYPHOON 
INTENSITY BETWEEN TAUS 36 AND 48. AFTER THIS POINT, A STEADY DECLINE 
IN INTENSITY IS EXPECTED AS TY 17W MOVES INTO AN AREA OF LOWER OCEAN
HEAT CONTENT (OHC), INCREASED VWS, AND A LESS FAVORABLE AREA OF
UPPER LEVEL OUTFLOW.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR
ALMOST THE ENTIRE FORECAST PERIOD, ALTHOUGH SPREAD INCREASES AROUND 
TAU 96 AND REACHES 300 NM AT TAU 120 BETWEEN THE OUTERMOST MEMBERS 
(GFS AND ECMWF). HOWEVER, THE REMAINDER OF MODEL GUIDANCE IS TIGHTLY 
GROUPED IN THE MIDDLE OF THE GFS AND ECMWF SOLUTIONS AND CENTERED 
JUST NORTH OF OKINAWA. A MAJORITY OF MODELS FAVOR A GRADUAL WESTWARD 
TURN BY TAU 96. THE OFFICIAL JTWC TRACK FORECAST IS PLACED WITH HIGH 
CONFIDENCE OUT TO TAU 72 AND MEDIUM CONFIDENCE THEREAFTER, CLOSELY IN 
LINE WITH THE MULTI-MODEL CONSENSUS, AI CONSENSUS, AND EXPERIMENTAL
GOOGLE DEEPMIND SOLUTIONS. INTENSITY MODEL GUIDANCE IS IN GOOD 
AGREEMENT IN THE SHORT TERM WITH ALL BUT GFS PREDICTING RI OUT TO TAU 
24 TO 36. SOLUTIONS DURING THE SUBSEQUENT SLOW WEAKENING PHASE FALL 
WITHIN A WIDER RANGE OF ABOUT 30 KTS. THUS, THE OFFICIAL JTWC 
INTENSITY FORECAST IS ASSESSED WITH HIGH CONFIDENCE OUT TO TAU 72 AND 
MEDIUM CONFIDENCE THEREAFTER, LYING ABOVE THE MULTI-MODEL CONSENSUS
THROUGHOUT AS CURRENT FAVORABLE CONDITIONS IN THE NEAR-TERM.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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