WDPN31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 037//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.2N 123.5E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 208 NM SOUTH-SOUTHEAST OF SHANGHAI, CHINA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TYPHOON 
(TY) 17W IS CURRENTLY TRAVELING WEST-SOUTHWESTWARD AT 06 KTS. ANIMATED 
ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SYSTEM WITH A LESS 
ORGANIZED CENTRAL DENSE OVERCAST (CDO) AND RESTRICTED POLEWARD OUTFLOW 
ALOFT. THERE HAVE BEEN NO OBSERVATIONS OF THE STORM CENTER BY HIGH-
RESOLUTION MICROWAVE SENSORS SINCE THE 262340Z SSMIS AND 262312Z GMI 
OVERPASSES, BOTH OF WHICH DETAILED AN INNER CORE ERODED ON THE 
NORTHEAST SIDE, A SLIGHT SOUTHWARD VORTEX TILT WITH HEIGHT, AND AN 
OBLONG, 25-30 NM WIDE LOWER-LEVEL EYE. GIVEN THE PERSISTENT 20-25 KTS 
OF NORTHERLY SHEAR, WHICH HAS ENABLED PLENTY OF DRY AIR TO ENTRAIN 
INTO THE CIRCULATION, THESE CHARACTERISTICS HAVE LIKELY PERSISTED. IN 
FACT, RADAR IMAGERY CONFIRMS THIS, SHOWING THAT THE ENTIRE NORTH SIDE 
OF THE EYEWALL HAS UNDERGONE SIGNIFICANT STRUCTURAL EROSION DUE TO THE 
SHEAR. FINALLY, A 270939Z RCM-1 SAR IMAGE ESTIMATED MAXIMUM SUSTAINED
WINDS OF 77 KTS. THE OVERALL ENVIRONMENT IS UNFAVORABLE, WITH WARM SEA 
SURFACE TEMPERATURES (SST) OF 27-29 DEGREES CELSIUS BEING STRONGLY 
OFFSET BY MODERATE VERTICAL WIND SHEAR (VWS). THE INITIAL POSITION IS 
ASSESSED WITH HIGH CONFIDENCE, HEDGED SLIGHTLY NORTH OF THE TIGHT 
BANDING OF THE CDO IN THE EIR IMAGERY AND THE OFFSHORE EYE IN THE 
RADAR IMAGERY TO ACCOUNT FOR VORTEX TILT. REFLECTING THE DEGRADATION 
OF THE CONVECTIVE STRUCTURE AND INCORPORATING THE RECENT SAR DATA, THE 
INITIAL INTENSITY HAS BEEN LOWERED TO 75 KTS WITH HIGH CONFIDENCE. 
THIS ASSESSMENT AGREES WITH THE MAJORITY T4.5 FIXES BUT IS ON THE LOW 
END OF THE OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHEASTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER THE INTERIOR OF MAINLAND
CHINA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 89 KTS AT 270700Z
   CIMSS ADT: 79 KTS AT 271200Z
   CIMSS AIDT: 77 KTS AT 271200Z
   CIMSS D-MINT: 84 KTS AT 271024Z
   CIMSS D-PRINT: 75 KTS AT 271200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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 WILL ACCELERATE, DOUBLING ITS TRANSLATION 
SPEED TO 12 KTS BY TAU 24, AS IT IS CAPTURED BY AN ANTICYCLONE 
POSITIONED SOUTH OF MONGOLIA. THIS STEERING MECHANISM WILL DRIVE THE 
SYSTEM ON A WEST-SOUTHWESTWARD TRAJECTORY, LEADING TO A LANDFALL OVER 
OR NEAR WENZHOU, CHINA, AS A STRONG TROPICAL STORM OR LOW-END TYPHOON. 
WHILE THE SYSTEM HAS JUST OVER 12 HOURS REMAINING OVER WARM OCEAN 
WATERS, THE COMBINATION OF VWS INCREASING TO 25-35 KTS AND LAND 
INTERACTION WILL LEAD TO RAPID WEAKENING AS IT APPROACHES THE COAST OF 
CENTRAL CHINA. THIS RAPID DECAY WILL CONTINUE ONCE INLAND, WITH 
DISSIPATION PREDICTED BY TAU 36. AS TY 17W APPROACHES LANDFALL, THE 
OVERALL WIND FIELD WILL CONTRACT DUE TO THE COMBINED EFFECTS OF DRY 
AIR ENTRAINMENT AND PERSISTENT VWS.

MODEL DISCUSSION: THE TRACKER GUIDANCE IS TIGHT THROUGH TAU 36. A
SUBTLE DIVERGENCE EXISTS, WITH THE PHYSICS-BASED MODELS PREFERRING A 
MORE ZONAL TRACK, WHILE THE AI MODELS DEPICT A SLIGHTLY STRONGER 
SOUTHWARD TURN. THE JTWC FORECAST TRACK IS PLACED WITH HIGH CONFIDENCE 
ALONG THE JTWC CONSENSUS (CONW) FOR THE FIRST 24 HOURS AND THEN LEANS 
TOWARD THE AI-BASED SOLUTIONS AT TAU 36. THE INTENSITY AIDS ARE IN 
EXCELLENT AGREEMENT, UNANIMOUSLY PREDICTING RAPID WEAKENING FROM TAU 0 
TO TAU 36 WITH A VERY TIGHT SPREAD OF 05 KTS. THEREFORE, THE JTWC 
INTENSITY FORECAST IS SET WITH HIGH CONFIDENCE ALONG THE CONSENSUS 
THROUGH TAU 24 AND THEN ALIGNS WITH THE HAFS-A AND GFS SOLUTIONS AT 
TAU 36.

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