Advisories

WDPN31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6N 132.3E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 248 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
(TY) 17W (SAUDEL) AS HAVING DEVELOPED A DISTINCT DRY SLOT ALONG THE
WESTERN EDGE OF THE EYEWALL, WHICH HAS SUBSTANTIALLY WEAKENED IT,
ALONG WITH DECREASING DEEP CONVECTION WITHIN THE WESTERN QUADRANT
CAUSED BY THE MID-LEVEL DRY AIR BEGINNING TO ENTRAIN INTO THE
SYSTEM. THE EYE IS BECOMING INCREASINGLY RAGGED AND HAS ALMOST
ENTIRELY FILLED WITH CLOUDS. ENVIRONMENTAL ANALYSIS REVEALS A
MARGINAL ENVIRONMENT, CHARACTERIZED BY MODERATE TO HIGH (20-25 KTS)
MID-LEVEL VERTICAL WIND SHEAR (VWS), SLIGHT MID-LEVEL DRY AIR
ENTRAINMENT, AND DECREASING UPPER LEVEL OUTFLOW, SLIGHTLY OFFSET BY
THE WARM (29-30 C) SEA SURFACE TEMPERATURES (SST). THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE RAGGED EYE IN
ANIMATED EIR. THE INITIAL INTENSITY OF 95 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE CIMSS AUTOMATED INTENSITY ESTIMATES
AND AGENCY DVORAK FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: 241302Z ASCAT DATA

CURRENT STEERING MECHANISM: THE SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) WHICH EXTENDS SOUTHEASTWARD FROM JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 101 KTS AT 241830Z
   CIMSS ADT: 87 KTS AT 241830Z
   CIMSS AIDT: 92 KTS AT 241830Z
   CIMSS D-MINT: 96 KTS AT 241712Z
   CIMSS D-PRINT: 92 KTS AT 241830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: SLIGHT MID-LEVEL DRY AIR ENTRAINMENT FROM THE
WEST

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: TY 17W (SAUREL) IS FORECAST TO CONTINUE
TRACKING NORTHWESTWARD WHILE IT REMAINS UNDER THE STEERING
INFLUENCE OF THE DEEP-LAYER STR STRETCHING SOUTHEASTWARD FROM
JAPAN. 17W IS EXPECTED TO PASS THROUGH THE RYUKU ISLANDS JUST
BEFORE TAU 24. BEGINNING AROUND TAU 24, 17W WILL ENCOUNTER A
WEAKNESS IN THE STR, CAUSING IT TO SLOW ITS SPEED OF ADVANCE IN THE
EAST CHINA SEA. SIMULTANEOUSLY, A STR CURRENTLY CENTERED OVER
EASTERN CHINA IS EXPECTED TO BUILD AND ASSUME STEERING AUTHORITY
OVER SAUDEL, INDUCING A SOUTHWESTWARD TRACK FROM TAU 36 THROUGH TAU
120. LANDFALL IN EASTERN CHINA IS ANTICIPATED BETWEEN TAU 72-96,
WITH DISSIPATION FORECAST NO LATER THAN TAU 120. REGARDING
INTENSITY, 17W IS ASSESSED TO BE IN ITS TERMINAL WEAKENING PHASE
PRIOR TO LANDFALL, WITH GRADUAL WEAKENING FORECAST TO OCCUR THROUGH
TAU 72 AND RAPID WEAKENING OVER LAND FORECAST FROM TAU 96-120. THE
ENVIRONMENT IS EXPECTED TO DETERIORATE THROUGHOUT THE FORECAST
PERIOD, WITH VWS REMAINING BETWEEN 20-30 KTS AND INCREASING DRY AIR
ENTRAINMENT FROM THE WEST FORCING ITS WAY INTO THE CORE.
ADDITIONALLY, UPPER LEVEL SUPPORT PROVIDED BY THE UPPER LEVEL
TROUGH IS REDUCING AS THE UPPER LEVEL TROUGH THAT PREVIOUSLY
PROVIDED SUPPORT IS FILLING AND SHIFTING WESTWARD. OUTFLOW IS
EXPECTED TO CONTINUE WORSENING THROUGHOUT THE FORECAST PERIOD,
CONTRIBUTING TO THE GRADUAL WEAKENING EXPECTED. DISSIPATION IS
FORECAST TO OCCUR BEFORE TAU 120 AS THE RUGGED TERRAIN SHREDS THE
SYSTEM.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH LANDFALL, AND LENDS HIGH CONFIDENCE TO THE JTWC
TRACK FORECAST FROM TAU 0-72. FOLLOWING TAU 72, TRACK GUIDANCE
DIVERGES AS LAND INTERACTION BEGINS TO INFLUENCE THE STORM. AS A
RESULT, THE JTWC TRACK FORECAST FROM TAU 72-120 IS PLACED WITH
MEDIUM CONFIDENCE. RELIABLE INTENSITY AIDS ARE IN VERY GOOD
AGREEMENT THROUGH TAU 72, WITH ONLY A 10 KT SPREAD BETWEEN MEMBERS.
THE JTWC INTENSITY FORECAST IS ASSESSED WITH HIGH CONFIDENCE FROM
TAU 0-72. AFTER TAU 72, INTENSITY GUIDANCE SPREAD INCREASES
SLIGHTLY AS MODELS DISAGREE OVER THE EXTENT OF WEAKENING OVER LAND.
AS A RESULT, THE JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM
CONFIDENCE FROM TAU 72-120.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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