Advisories

WDPN31 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 027//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.0N 131.1E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 180 NM EAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TYPHOON (TY)
17W  (SAUDEL) CONTINUING TO TRACK TOWARDS THE RYUKU ISLANDS. THE
EYE IS NOW COMPLETELY FILLED AND HAS OPENED IN THE WESTERN
QUADRANT, AS EVIDENCED BY THE 242300Z GPM GMI IMAGERY. THE SLIGHT
DRY AIR ENTRAINMENT FROM THE WEST CONTINUES TO EAT AWAY AT THE
SYSTEM, CAUSING NOTICEABLY LESS DEEP CONVECTION ALONG THE WESTERN
FLANK. ENVIRONMENTAL ANALYSIS REVEALS A MARGINALLY FAVORABLE
ENVIRONMENT, CHARACTERIZED BY LOW TO MODERATE (15-20 KTS) VERTICAL
WIND SHEAR (VWS), WARM (29-30 C) SEA SURFACE TEMPERATURES (SST),
AND MODERATE RADIAL OUTFLOW, OFFSET BY THE DRY AIR ENTRAINMENT. THE
VWS HAS BACKED OFF SLIGHTLY IN THE PAST 6 HOURS, CONTRIBUTING TO
THE IMPROVED ENVIRONMENTAL CONDITIONS. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE 242300Z GMI DATA. THE
INITIAL INTENSITY OF 90 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE EARLIER 242105Z RCM-1 SAR DATA REVEALING MAXIMUM WINDS
OF 93 KTS IN THE NORTHERN SEMICIRCLE, SUPPORTED BY THE AGENCY
DVORAK FIXES AND CIMSS AUTOMATED INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RCTP: T5.5 - 102 KTS
   CIMSS ADT: 82 KTS AT 250000Z
   CIMSS AIDT: 89 KTS AT 250000Z
   CIMSS D-MINT: 86 KTS AT 242259Z
   CIMSS D-PRINT: 86 KTS AT 240000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: SLIGHT 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 AFTER
TAU 12 AT AN INTENSITY OF 85 KTS. BETWEEN TAU 12-24, 17W WILL
ENCOUNTER A WEAKNESS IN THE STEERING STR, CAUSING IT TO SLOW ITS
SPEED OF ADVANCE IN THE EAST CHINA SEA BETWEEN TAU 24-48.
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,
ACCELERATING SAUREL TOWARDS THE COAST AS THE RIDGE BUILDS. LANDFALL
IN EASTERN CHINA IS ANTICIPATED AROUND TAU 72, 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 UNTIL LANDFALL, WHICH WILL FORCE
ADDITIONAL DRY AIR INTO THE CORE. THE SSTS AND OCEAN HEAT CONTENT
WILL REMAIN FAVORABLE UNTIL 72, SLIGHTLY BALANCING THE VWS AND DRY
AIR. DISSIPATION IS FORECAST TO OCCUR BEFORE TAU 120 AS THE RUGGED 
TERRAIN SHREDS THE SYSTEM.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN VERY
STRONG AGREEMENT THROUGH TAU 24, CONTRIBUTING TO HIGH CONFIDENCE AS
SAUREL PASSES THROUGH THE RYUKU ISLANDS. GUIDANCE REMAINS IN GOOD
AGREEMENT THROUGH LANDFALL AT TAU 72, 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 ALL MEMBERS DEPICTING A GRADUAL
WEAKENING UNTIL TAU 72, FOLLOWED BY RAPID WEAKENING OVER LAND. 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. THE JTWC LIES VERY CLOSE TO THE
MULTI-MODEL CONSENSUS, HAFS-A SOLUTION, AND COAMPS-TC (GFS BOUNDARY
CONDITION) SOLUTION, WITH THE GFS DETERMINISTIC AND COAMPS-TC
(NAVGEM BOUNDARY CONDITIONS) ALSO NEARBY.

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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