Advisories

WDPN31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.6N 144.8E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 1025 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 38 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
17W (SAUDEL) WITH A SLIGHTLY RAGGED EYE THAT HAS CONTINUED TO WARM
OVER THE PAST 6 HOURS AS IT PASSES WEST OF THE NORTHERNMOST MARIANA
ISLANDS. THE STRONGEST CONVECTIVE ACTIVITY IS LOCATED WITHIN THE 
WESTERN SEMICIRCLE OF THE EYEWALL WITH A WEAKNESS IN THE NORTHERN
SEMICIRCLE. ANIMATED WATER VAPOR IMAGERY SHOWS DEFINED CIRRUS 
FILAMENTS EXPANDING OUTWARD TO THE NORTH, AND IS INDICATIVE OF A 
STRONG POLEWARD OUTFLOW CHANNEL. 17W HAS CONTINUED TO RAPIDLY 
INTENSIFY, NOW HAVING INTENSIFIED 35 KTS OVER THE PAST 24 HOURS. THE 
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN 
ANIMATED EIR IMAGERY. THE INITIAL INTENSITY OF 105 KTS IS ASSESSED 
WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS 
INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES 
THAT 17W IS IN A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED BY ROBUST 
POLEWARD OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, AND VERY 
WARM (30-31 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE NORTHEAST


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 96 KTS AT 221040Z
   CIMSS ADT: 90 KTS AT 221200Z
   CIMSS AIDT: 86 KTS AT 221200Z
   CIMSS D-MINT: 106 KTS AT 221222Z
   CIMSS D-PRINT: 105 KTS AT 221200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

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 WEST-NORTHWESTWARD
ALONG THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE 
NORTHEAST THROUGH TAU 48. NEAR TAU 48, THE STR IS EXPECTED TO MERGE
WITH ANOTHER STR POSITIONED OVER SOUTHERN JAPAN. THE COMBINED STEERING 
INFLUENCE OF THE RIDGING COMPLEX WILL KEEP 17W ON A WEST-NORTHWESTWARD 
TRAJECTORY THROUGH TAU 96. THE TIMING OF LANDFALL OVER OKINAWA HAS 
REMAINED CONSISTENT WITH THE PREVIOUS FORECASTS, AND IS EXPECTED TO 
OCCUR JUST BEFORE TAU 96. AFTERWARD, TRACK SPEEDS ARE EXPECTED TO SLOW 
THROUGH TAU 120 AS THE PRIMARY STEERING MECHANISM TRANSITIONS TO A 
SUBTROPICAL RIDGE POSITIONED OVER EASTERN CHINA. A TURN TO THE 
SOUTHWEST, TOWARD NORTHERN TAIWAN IS THEN LIKELY IN THE EXTENDED 
FORECAST. IN TERMS OF INTENSITY, 17W IS FORECAST TO CONTINUE 
INTENSIFYING THROUGH TAU 36 TO A PEAK OF AROUND 130 KTS AS THE 
ENVIRONMENT REMAINS HIGHLY CONDUCIVE. AFTER TAU 36, THE POLEWARD 
OUTFLOW CHANNEL WILL WEAKEN AND NORTHWESTERLY SHEAR WILL BEGIN TO 
INCREASE, CAUSING 17W TO START ON A GRADUAL WEAKENING TREND AS IT 
APPROACHES OKINAWA. FURTHER WEAKENING WITHIN THE EAST CHINA SEA IS 
EXPECTED DUE TO INCREASING SHEAR AND DRY AIR INDUCED BY A STRONG RIDGE 
OVER EASTERN CHINA. 

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH
TAU 72 WITH THE ONLY NOTABLE OUTLIER BEING NAVGEM, WHICH TRACKS THE
VORTEX MUCH FURTHER SOUTH. DISCOUNTING NAVGEM, CROSS-TRACK SPREAD AT 
TAU 72 IS MEASURED TO BE 160 NM. AFTER TAU 72, CROSS-TRACK SPREAD 
INCREASES TO AROUND 200 NM WITH THE ECMWF AND GFS BOTH MAKING A FASTER 
SOUTHWESTWARD TURN THAN THE EC-AIFS AND EXPERIMENTAL GOOGLE DEEPMIND. 
THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE ADJUSTED CONSENSUS WITH 
HIGH CONFIDENCE THROUGH TAU 72 AND THEN HEDGED SLIGHTLY CLOSER TO THE 
GOOGLE DEEPMIND AND EC-AIFS THROUGH TAU 120 WITH MEDIUM CONFIDENCE. 
INTENSITY GUIDANCE REMAINS SPLIT BETWEEN THE RAPID INTENSIFICATION 
(RI) AIDS AND THE NON-RI AIDS. THE RI AIDS SHOW A PEAK OF 130-150 KTS 
AT TAU 36 WHILE HAFS-A ONLY SHOWS A PEAK OF 115 KTS. THE JTWC 
INTENSITY FORECAST IS PLACED CLOSER TO THE RI AIDS THROUGH TAU 36 DUE  
TO THE EXPECTED HIGHLY FAVORABLE ENVIRONMENT. MODELS THEN AGREE ON 
STEADY WEAKENING FROM TAU 48 ONWARD AND THE JTWC INTENSITY FORECAST 
FOLLOWS SUIT.

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