Advisories

WDPN31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 035//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.5N 124.9E
   INITIAL INTENSITY: 75 KTS
   GEOGRAPHIC REFERENCE: 195 NM NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS ONGOING
DISRUPTION OF DEEP CONVECTION WITHIN THE NORTHERN PORTION OF THE
CIRCULATION, WHERE NORTHERLY UPPER-LEVEL FLOW ASSOCIATED WITH A 
BUILDING SUBTROPICAL RIDGE TO THE NORTHWEST IS INDUCING PERSISTENT 
VERTICAL WIND SHEAR AND ENABLING DRIER AIR TO WRAP IN FROM THE 
SURROUNDING ENVIRONMENT. HOWEVER, THE CORE OF THE CIRCULATION IS SO 
FAR WITHSTANDING THE SHEAR AND MAINTAINING A VISIBLE AND MORE COMPACT
(15 NM DIAMETER) EYE. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON SSMIS 37 GHZ MICROWAVE SATELLITE IMAGERY FROM 
262148Z AND 262342Z CLEARLY DEPICTING THE LOW-LEVEL PORTION OF THE 
EYE. THE INITIAL INTENSITY OF 75 KTS IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE RANGE OF SUBJECTIVE DVORAK AND AUTOMATED 
INTENSITY FIXES LISTED BELOW AND PERSISTENCE FROM THE PREVIOUS 
ANALYSIS.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK AND PERSISTENCE 

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: 82 KTS AT 262342Z
   CIMSS ADT: 90 KTS AT 270000Z
   CIMSS AIDT: 75 KTS AT 270000Z
   CIMSS D-MINT: 82 KTS AT 262342Z
   CIMSS D-PRINT: 81 KTS AT 270100Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: INTRUSION OF DRIER AIR INTO NORTHERN PORTION OF
THE CIRCULATION

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON (TY) 17W HAS TURNED TOWARD A WEST-
SOUTHWESTWARD TRACK AS A LARGE STR CENTERED OVER NORTH-CENTRAL CHINA 
BECOMES THE DOMINANT STEERING MECHANISM. RIDGING TO THE NORTHWEST WILL 
STEER THE SYSTEM THROUGHOUT THE FORECAST PERIOD, CARRYING THE CENTER 
INLAND ACROSS SOUTHERN ZHEJIANG PROVINCE JUST AFTER TAU 24. SOME 
WEAKENING IS ANTICIPATED PRIOR TO LANDFALL AS THE DUAL INFLUENCES OF 
VERTICAL WIND SHEAR AND ENTRAINMENT OF DRIER AIR PERSIST, ALTHOUGH THE 
SYSTEM IS EXPECTED TO HOLD UP AS A STRONG TROPICAL STORM OR MINIMAL 
TYPHOON THANKS TO PASSAGE OVER SUFFICIENTLY WARM WATER AND FAVORABLE 
EQUATORWARD OUTFLOW. FOLLOWING LANDFALL, PASSAGE OVER LAND WILL LEAD 
TO DISSIPATION BY TAU 60.

MODEL DISCUSSION: MODEL TRACK AND INTENSITY FORECASTS ARE IN VERY
GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH NO EXCEPTIONALLY
NOTEWORTHY DEVIATIONS ASIDE FROM A MINIMAL SPREAD BETWEEN TRADITIONAL 
DYNAMICAL MODELS AND AI GUIDANCE AFTER TAU 48. THE CURRENT JTWC 
FORECAST IS PLACED WITH HIGH CONFIDENCE IN TERMS OF BOTH TRACK AND 
INTENSITY GIVEN BROAD MODEL SUPPORT AND A STRAIGHTFORWARD TRACK AND 
INTENSITY SCENARIO.

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