Advisories

WDPN31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.2N 129.0E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 77 NM EAST-NORTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 17W IS CURRENTLY MAKING LANDFALL OVER THE JAPANESE
ISLAND OF OKINOERABUJIMA, WHERE THE SEA LEVEL PRESSURE HAS DROPPED
TO 965 MB AT 251200Z, ACCOMPANIED BY A SUSTAINED WIND OF 60 KTS AND
A GUST OF 85 KTS. IT IS PROBABLE THAT THE MAXIMUM SUSTAINED WINDS
ARE OCCURRING WITHIN THE CHANNEL BETWEEN OKINOERABUJIMA AND
TOKUNOSHIMA. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
DEPICTS LITTLE CHANGE IN STRUCTURE, CONSISTING OF A COMPACT CENTRAL
DENSE OVERCAST FLANKED BY EXTENSIVE SPIRAL BANDS. A PERSISTENT DRY
SLOT IS WEDGED INTO THE WESTERN SEMICIRCLE AS A RESULT OF 20-25 KTS
OF NORTHWESTERLY VERTICAL WIND SHEAR (VWS), ENTRAINING DRY AIR INTO
THE VORTEX IN THE 500-300 MB LAYER. A 250914Z WSF-M MWI 37 GHZ
IMAGE CONFIRMS THIS STRUCTURAL DEGRADATION, REVEALING THAT THE
INNER CORE IS OPEN ON THE SOUTHWESTERN SIDE. THIS SHEAR IS
OFFSETTING ANY DEVELOPMENT POTENTIAL OFFERED BY THE WARM SEA
SURFACE TEMPERATURES (SST) OF 28-29 DEGREES CELSIUS. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON RADAR IMAGERY.
COINCIDENT SAR PASSES FROM RCM-1 AND SENTINEL-1C ESTIMATED PEAK
WINDS OF 90-95 KTS, WHILE SUBJECTIVE DVORAK FIXES OF T4.5-5.0
SUGGEST 77-90 KTS. THE OBJECTIVE ESTIMATES FROM CIMSS RANGE FROM 53
KTS TO 83 KTS. BASED ON A BLEND OF THESE SOURCES, THE INITIAL
INTENSITY IS SET AT 85 KTS WITH MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A SUBTROPICAL
RIDGE (STR) CENTERED SOUTH OF CENTRAL HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 90 KTS AT 250930Z
   CIMSS ADT: 53 KTS AT 251200Z
   CIMSS AIDT: 67 KTS AT 251200Z
   CIMSS D-MINT: 83 KTS AT 250946Z
   CIMSS D-PRINT: 77 KTS AT 251200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: THE WESTWARD MIGRATION OF THE STR EAST OF TY
17W WILL CEASE IN THE NEXT 12 HOURS. THIS WILL ALLOW THE WESTERN
EXTENSION OF THE RIDGE TO BECOME THE DOMINANT STEERING MECHANISM,
CAUSING TY 17W TO TURN WESTWARD AND DECELERATE FROM 11 KTS TO
APPROXIMATELY 06 KTS OVER THE NEXT 36 HOURS. FROM TAU 36 TO TAU 96,
AN ANTICYCLONE OVER THE INTERIOR OF CHINA WILL TAKE CONTROL,
GUIDING THE SYSTEM ON A WEST-SOUTHWESTWARD TRAJECTORY WITH A FASTER
MOTION TOWARD LANDFALL. WHILE WARM OCEAN WATERS REMAIN AHEAD OF THE
STORM, GRADUAL WEAKENING WILL TAKE PLACE THROUGH TAU 24. THIS WILL
BE DRIVEN BY PERSISTENT, MODERATE-TO-HIGH VWS, WHICH IS ACTIVELY
ENTRAINING DRY AIR INTO THE CIRCULATION. A BRIEF REPRIEVE IN THE
SHEAR BETWEEN TAU 24 AND TAU 36 WILL ALLOW THE INTENSITY TO LEVEL
OFF. HOWEVER, AFTER THIS WINDOW, MODERATE-TO-HIGH VWS WILL RETURN.
THIS, COMBINED WITH INCREASING LAND INTERACTION, WILL LEAD TO A
FASTER WEAKENING TREND. THE SYSTEM WILL RAPIDLY DETERIORATE ONCE
OVER LAND, DISSIPATING BY TAU 96.

MODEL DISCUSSION: MODELS HAVE COME INTO BETTER AGREEMENT IN THE
LONG-RANGE FORECAST. HAFS-A AND NAVGEM BOUND THE EQUATORWARD SIDE
OF THE GUIDANCE ENVELOPE, WHILE THE ECENS AND UKMET ENSEMBLE MEANS
ANCHOR ON THE POLEWARD EDGE. THE JTWC FORECAST TRACK IS POSITIONED
WITH MEDIUM CONFIDENCE NEAR THE AI CONSENSUS, WHICH RESIDES NEAR
THE MIDDLE OF THIS ENVELOPE. THE EXPERIMENTAL GOOGLE DEEPMIND MODEL
IS SLIGHTLY NORTH OF THE FORECAST TRACK. THE SPREAD AMONG THE
INTENSITY AIDS HAS INCREASED. HAFS-A NOW CALLS FOR A SLOW WEAKENING
TREND, WHILE DEEPMIND IS NO LONGER AS AGGRESSIVE IN ITS WEAKENING
SOLUTION AS IT WAS 06 HOURS AGO. THE JTWC INTENSITY FORECAST IS SET
WITH MEDIUM CONFIDENCE NEAR THE MULTI-MODEL CONSENSUS, ALIGNING
MOST CLOSELY WITH THE SOLUTIONS FROM DEEPMIND AND GFS.

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