Advisories

WDPN31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 036//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.4N 124.2E
   INITIAL INTENSITY: 80 KTS
   GEOGRAPHIC REFERENCE: 245 NM NORTHEAST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY) 
17W (SAUDEL) TRANSITING WEST-NORTHWESTWARD TOWARD ZHEJIANG PROVINCE, 
CHINA. DESPITE MARGINALLY UNFAVORABLE ENVIRONMENTAL CONDITIONS, 
PRIMARILY DRIVEN BY MODERATE NORTHEASTERLY VERTICAL WIND SHEAR (VWS) 
AND SIGNIFICANT DRY AIR INTRUSION, THE VORTEX HAS MANAGED TO REMAIN 
STRUCTURALLY COHERENT. FOLLOWING A BRIEF PERIOD OF CONVECTIVE EYE-
FILL, THE CYCLONE HAS RE-ESTABLISHED A BANDING EYE FEATURE, INDICATING 
SUSTAINED INTENSITY. WARM SEA SURFACE TEMPERATURES (SST) OF 28-29 C 
AND GOOD EQUATORWARD OUTFLOW OFFSET THE OTHERWISE DEGRADING 
THERMODYNAMIC ENVIRONMENT. THE INITIAL POSITION IS ASSESSED WITH HIGH 
CONFIDENCE UTILIZING VISIBLE SATELLITE IMAGERY, LENDING TO A TIGHT 
CONSENSUS OF AGENCY POSITION FIXES. THE INITIAL INTENSITY OF 80 KTS IS 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON A COMBINATION OF OBJECTIVE 
AND SUBJECTIVE AIDS LISTED BELOW.

INITIAL WIND RADII BASIS: 270111Z METOP-C ASCAT AND 270109Z METOP-C
UHR ASCAT DATA

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 93 KTS AT 270444Z
   CIMSS ADT: 90 KTS AT 270540Z
   CIMSS AIDT: 76 KTS AT 270600Z
   CIMSS D-MINT: 84 KTS AT 270530Z
   CIMSS D-PRINT: 80 KTS AT 270600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT AND PERSISTENT NORTHEASTERLY
VERTICAL WIND SHEAR

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 CONTINUE TRACKING WEST-
SOUTHWESTWARD TOWARD LANDFALL OVER EAST-CENTRAL CHINA, LIKELY NEAR THE 
CITY OF TAIZHOU. AN INCREASINGLY HOSTILE ENVIRONMENT, DRIVEN PRIMARILY 
BY ESCALATING VWS AND PERSISTENT MID-LEVEL DRY-AIR ENTRAINMENT, WILL 
RESULT IN GRADUAL WEAKENING PRIOR TO LANDFALL. AFTER THE STR ANCHORED 
TO THE NORTHEAST STEERS THE SYSTEM OVER LAND, TERMINAL WEAKENING WILL 
PROGRESS AT A MUCH FASTER RATE, ACCELERATED BY THE FRICTIONAL EFFECTS 
OF ROUGH LAND INTERACTION. THE SYSTEM IS EXPECTED TO WEAKEN 
SIGNIFICANTLY BY TAU 48 AS THE VORTEX TRAVERSES HIGHER TERRAIN, WITH 
COMPLETE DISSIPATION PROJECTED TO OCCUR AT OR PRIOR TO TAU 60.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE EXHIBITS EXCELLENT 
AGREEMENT, AS ALL AVAILABLE DYNAMIC MODELS RESOLVE A SIMILAR LANDFALL 
TIMELINE AND GEOGRAPHIC LOCATION, FOLLOWED BY A SUBSEQUENT 
SOUTHWESTWARD VEER OVER LAND. AS SUCH, THE OFFICIAL JTWC TRACK 
FORECAST IS POSITIONED WITH HIGH CONFIDENCE, SUPPORTED BY A NARROW 70 
NM CROSS-TRACK SPREAD AT THE END OF THE FORECAST PERIOD. THE INTENSITY 
FORECAST IS ALSO ASSESSED WITH HIGH CONFIDENCE. WHILE ALL AVAILABLE 
MODEL GUIDANCE SOLUTIONS INDICATE RAPID DECAY THROUGH TAU 36, THE 
TEMPORAL TIMELINE OF COMPLETE DISSIPATION RANGES NARROWLY BETWEEN TAU 
48 AND TAU 60. THE OFFICIAL JTWC INTENSITY FORECAST IS HEDGED BETWEEN 
THE GUIDANCE OF HAFS AND DETERMINISTIC GFS, ALIGNING CLOSELY WITH THE 
MULTI-MODEL CONSENSUS.

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