Advisories

WDPN31 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
 
SUMMARY:
   INITIAL POSITION: 17.9N 146.5E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 167 NM NORTH-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 17W
(SAUDEL) WITH EXPANDING CONVECTIVE BANDING TO THE NORTH AND
NORTHEAST AND A WEDGE OF DRIER AIR WRAPPING INTO THE CIRCULATION FROM 
THE SOUTHEAST. 91 GHZ AND 37 GHZ IMAGES FROM A 212131Z SSMIS PASS 
REVEAL A MICROWAVE EYE TILTED SLIGHTLY TO THE NORTHWEST WITH HEIGHT. 
ADDITIONALLY, A 212011Z RCM-2 SAR PASS REVEALS AN INCREASINGLY 
SYMMETRICAL WIND FIELD WITH 64 KT WINDS ALMOST FULLY WRAPPED AROUND 
THE CORE, AND MORE EXPANSIVE AREA OF HIGHER WINDSPEEDS SITUATED 
WITHIN THE NORTHEAST QUADRANT. ENVIRONMENTAL CONDITIONS REMAIN 
FAVORABLE WITH WARM (29-30) SEA SURFACE TEMPERATURES, LOW (10-15 KTS) 
VERTICAL WIND SHEAR (VWS), AND ENHANCED OUTFLOW ALOFT FACILITATED BY 
AN UPPER LEVEL TROUGH TO THE NORTH, OFFSET ONLY BY THE NOTED RECENT 
INTRUSION OF DRIER AIR FROM THE SOUTHEAST. THE INITIAL POSITION IS 
PLACED WITH HIGH CONFIDENCE BASED ON THE COMBINED MSI, MICROWAVE 
IMAGERY, AND AGENCY FIXES. THE INITIAL INTENSITY IS ASSESSED WITH 
HIGH CONFIDENCE BASED ON THE SAR DATA, SLIGHTLY ABOVE A CONSENSUS OF 
THE AGENCY DVORAK FIXES AND AUTOMATED INTENSITY FIXES LISTED BELOW.
 
INITIAL WIND RADII BASIS: 212011Z RCM-2 SAR PASS
 
CURRENT STEERING MECHANISM: WESTWARD EXTENSION OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTHEAST
 
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 59 KTS AT 212330Z
   CIMSS AIDT: 56 KTS AT 212330Z
   CIMSS D-MINT: 74 KTS AT 212330Z
   CIMSS D-PRINT: 85 KTS AT 212330Z
 
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 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 BEGIN A WESTWARD TURN IN
THE SHORT-TERM AS A WESTWARD EXTENSION OF THE SUBTROPICAL RIDGE (STR) 
CENTERED TO THE NORTHEAST MERGES WITH AN STR CENTERED OVER KYUSHU. 
THIS RIDGING COMPLEX IS EXPECTED TO REMAIN THE PRIMARY STEERING 
INFLUENCE UNTIL AROUND TAU 96, AFTER WHICH RIDGING TO THE NORTHWEST 
IS EXPECTED TO DOMINATE. REGARDING INTENSITY, STEADY INTENSIFICATION 
WILL LIKELY CONTINUE OUT TO TAU 24 AS TY 17W REMAINS IN AN AREA OF 
HIGH OCEAN HEAT CONTENT, LOW VWS, AND FAVORABLE OUTFLOW ALOFT. TY 17W 
IS EXPECTED TO PEAK AT OR NEAR SUPER TYPHOON INTENSITY BETWEEN TAUS 
36 AND 48, FOLLOWED BY A WEAKENING PHASE AS IT ENCOUNTERS INCREASED 
VWS, LOWER OHC, AND LESS FAVORABLE OUTFLOW ALOFT.
 
MODEL DISCUSSION: TRACK MODEL GUIDANCE REMAINS IN GOOD AGREEMENT IN
THE SHORT-TERM AND HAS CONSOLIDATED A BIT IN THE LONG-TERM, WITH A 
CROSS TRACK SPREAD OF 285 NM AT TAU 120. NOTABLY, ALL MODELS NOW 
DEPICT A SLIGHT WEST-SOUTHWESTWARD TURN BETWEEN TAUS 96 AND 120. SOME 
UNCERTAINTY REMAINS REGARDING REORIENTATION OF THE RIDGING COMPLEX 
BETWEEN JAPAN AND CENTRAL CHINA. GFS AND THE GEFS ENSEMBLE MEAN 
REMAIN THE NORTHERNMOST TRACKS, DEPICTING THE STR OVER KYUSHU 
RETREATING AND AN STR CENTERED OVER CENTRAL CHINA BUILDING EASTWARD 
TO STEER THE SYSTEM. ON THE SOUTH END OF THE GUIDANCE, ECMWF DEPICTS 
THE STR OVER KYUSHU COMBINING WITH THE STR OVER CENTRAL CHINA 
RESULTING IN STRONGER AND MORE CONTINUOUS RIDGING TO THE NORTH. THE 
BULK OF GUIDANCE CONTINUES TO DEPICT A TRACK OVER OR NEAR OKINAWA. 
THE OFFICIAL JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE OUT 
TO TAU 72 AND MEDIUM CONFIDENCE THEREAFTER, AND IS CLOSELY ALIGNED 
WITH THE MULTI-MODEL CONSENSUS AND AI GUIDANCE. MODEL INTENSITY 
GUIDANCE IS IN GOOD AGREEMENT REGARDING A SHORT-TERM INCREASE AND A 
PEAK BETWEEN TAUS 36 AND 48, WITH PEAK INTENSITIES RANGING FROM 95 
KTS TO 155 KTS. THE GENERAL WEAKENING TREND THEREAFTER IS ALSO 
DEPICTED ACROSS ALL MODELS, BUT A SPREAD OF ABOUT 40 KTS REMAINS 
THROUGHOUT. THE OFFICIAL JTWC INTENSITY FORECAST IS THUS ASSESSED 
WITH MEDIUM CONFIDENCE THROUGHOUT THE FORECAST PERIOD.

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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