Advisories

WDPN31 PGTW 260900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 032//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.3N 126.5E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 128 NM NORTH-NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON 17W
ON A WESTWARD TRACK TOWARD CENTRAL CHINA AT 09 KTS. A MOSTLY
CLOUD-FILLED, 40 NM WIDE EYE IS EMBEDDED WITHIN A RAGGED CENTRAL
DENSE OVERCAST. THE UPPER-LEVEL OUTFLOW IS MEAGER, STRONGEST TOWARD
THE NORTHEAST, DUE TO THE PRESENCE OF 15-20 KTS OF VERTICAL WIND
SHEAR (VWS). A 260704Z SSMIS PASS INDICATED A WEAKNESS IN THE
WESTERN SIDE OF THE EYEWALL AND A SLIGHT EASTWARD TILT OF THE
VORTEX WITH HEIGHT, WHICH TRACKS WITH THE EFFECTS OF SHEAR. THE
ENVIRONMENT IS MARGINALLY FAVORABLE, CHARACTERIZED BY WARM SEA
SURFACE TEMPERATURES (SST) OFFSET BY MODERATE VWS. THE INITIAL
POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE OBSCURED
EYE IN THE MSI. A 260105Z ASCAT-B UHR IMAGE REVEALED A SWATH OF 85
KT WINDS ALONG THE NORTHERN SIDE OF THE EYEWALL. THE INITIAL
INTENSITY IS SET AT 85 KTS BASED ON THE ASCAT-B UHR DATA AND THE
HIGH END OF THE SUBJECTIVE DVORAK AND OBJECTIVE INTENSITY
ESTIMATES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK SUBTROPICAL RIDGE (STR) POSITIONED
TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 85 KTS AT 260700Z
   CIMSS ADT: 72 KTS AT 260610Z
   CIMSS AIDT: 68 KTS AT 260610Z
   CIMSS D-MINT: 70 KTS AT 260504Z
   CIMSS D-PRINT: 76 KTS AT 260530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: ALTHOUGH TY 17W JOGGED NORTHWARD IN THE PAST
06 HOURS, THE FORECAST TRACK PHILOSOPHY REMAINS UNCHANGED. THE
LATEST ANIMATED MSI INDICATES THAT THE SYSTEM HAS RESUMED A
WESTWARD TRAJECTORY. A WEAK STR TO THE NORTH WILL STEER THE SYSTEM
WESTWARD WITH A LOWER FORWARD SPEED OVER THE NEXT 12 HOURS. BEYOND
12 HOURS, THE VORTEX WILL ENCOUNTER AN ANTICYCLONE OVER THE
INTERIOR OF CHINA. THE RESULT WILL BE AN EQUATORWARD SHIFT IN THE
TRACK AND A SLIGHTLY HIGHER FORWARD MOTION, LEADING TO A LANDFALL
NEAR WENZHOU, CHINA, BETWEEN TAU 36 AND TAU 48. THE INTENSITY OF TY
17W HAS BEEN NEAR STEADY STATE FOR THE PAST 24 HOURS, SUCCESSFULLY
COUNTERACTING THE NEGATIVE EFFECTS OF SHEAR. THE VWS WILL INCREASE
OVER THE NEXT 48 HOURS, LEADING TO A WEAKENING TREND UNTIL
LANDFALL. THE SYSTEM WILL RAPIDLY DECAY OVER LAND, DISSIPATING BY
TAU 72.

MODEL DISCUSSION: THE MODEL SPREAD IS RATHER LARGE AFTER LANDFALL,
OWING TO UNCERTAINTIES ASSOCIATED WITH THE STRENGTH OF THE
ANTICYCLONE OVER CHINA. THE PHYSICS-BASED MODELS PREFER A MORE
ZONAL TRACK INLAND, WHILE THE AI MODELS FAVOR A STRONGER
EQUATORWARD TURN. THE JTWC TRACK FORECAST IS POSITIONED NEAR THE
CONSENSUS (CONW) THROUGH TAU 24 AND THEN LEANS TOWARD THE AI
CONSENSUS FOR THE REMAINDER OF THE PERIOD WITH MEDIUM CONFIDENCE.
HAFS-A IS THE ONLY RELIABLE INTENSITY AID THAT HOLDS THE INTENSITY
FOR ANOTHER 12 HOURS, WHILE THE VAST MAJORITY SHOWS IMMINENT
WEAKENING. THE DECAY RATE ACCELERATES THROUGH THE FORECAST PERIOD,
AND THE JTWC INTENSITY FORECAST REFLECTS THIS TREND WITH HIGH
CONFIDENCE.

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