Advisories

WDPN31 PGTW 232100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.2N 137.9E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 584 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN 
APPROXIMATELY 15NM WIDE EYE FEATURE, WHICH IN THE MOST RECENT FRAMES OF 
EIR APPEARS TO BE SHRINKING ONCE AGAIN. THE EYEWALL REPLACEMENT CYCLE 
(ERC) WHICH STARTED YESTERDAY IS LIKELY ONGOING, ALTHOUGH A LACK OF 
RECENT MICROWAVE IMAGERY MAKES DETERMINATION OF THE CURRENT STATUS 
CHALLENGING. HOWEVER, THE OVERALL STRUCTURAL APPEARANCE OF THE SYSTEM 
IN THE EIR ALONG WITH A COMPARISON TO A 10 HOUR OLD MICROWAVE IMAGE 
SUGGESTS THAT THE ERC HAS NOT YET FULLY COMPLETED. ANIMATED WATER VAPOR 
IMAGERY DEPICTS AN UPPER-LEVEL ANTICYCLONE DRAPED ACROSS THE NORTH-
NORTHEASTERN SIDE OF THE SYSTEM, INDUCING LIGHT EASTERLY FLOW ALOFT AND 
EASTERLY SHEAR OVER TOP OF TY 17W. THE INITIAL POSITION IS ASSESSED 
WITH HIGH CONFIDENCE BASED ON THE EYE IN THE EIR. THE INITIAL INTENSITY 
IS ASSESSED WITH MEDIUM CONFIDENCE, BASED ON A BLEND OF THE OBJECTIVE 
AND SUBJECTIVE INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL 
CONDITIONS ARE FAVORABLE OVERALL, WITH LIGHT WIND SHEAR, WARM SSTS, 
HIGH OHC AND MODERATE OUTFLOW ALOFT, OFFSET BY THE IMPACTS OF THE 
ONGOING ERC.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) WHICH EXTENDS SOUTHEASTWARD FROM SOUTHERN
JAPAN TO A POSITION NORTHEAST OF GUAM. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   CIMSS SATCON: 116 KTS AT 231830Z
   CIMSS ADT: 112 KTS AT 231830Z
   CIMSS AIDT: 105 KTS AT 231830Z
   CIMSS D-MINT: 105 KTS AT 231646Z
   CIMSS D-PRINT: 108 KTS AT 231800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: ONGOING EYEWALL REPLACEMENT CYCLE (ERC)

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: TYPHOON (TY) 17W (SAUDEL) CONTINUES TO TRACK WEST-
NORTHWESTWARD ALONG THE SOUTHWESTERN FLANK OF THE EXPANSIVE STR 
SITUATED TO THE NORTHEAST. NO SIGNIFICANT CHANGES IN TRACK OR SPEED IS 
EXPECTED FOR THE 36 HOURS AS THE STR IS FORECAST TO REMAIN FIRMLY 
ENTRENCHED. AROUND TAU 36 HOWEVER, THE RIDGING PATTERN BEGINS TO SHIFT, 
WITH A WEAKNESS OR BREAK IN THE RIDGE DEVELOPING OVER SOUTH KOREA. AS 
TY 17W APPROACHES THE RYUKYU ISLANDS, IT WILL BEGIN TO SLOW DOWN WHILE 
CONTINUING TO GAIN LATITUDE. AROUND TAU 60, THE SYSTEM REACHES AN 
INFLECTION POINT, REACHING ITS FURTHEST POLEWARD EXTENT, AND BEGINS TO 
GRADUALLY TURN WESTWARD AS THE PRIMARY STEERING INFLUENCE SHIFTS TO A 
BUILDING RIDGE OVER EASTERN CHINA. AFTER TAU 72, THE STEERING SHIFT 
WILL BE COMPLETE, AND TY 17W WILL QUICKLY TURN SOUTHWESTWARD ALONG THE 
SOUTHEASTERN FLANK OF THE BUILDING RIDGE TO THE WEST. THE SYSTEM IS 
EXPECTED TO MAKE LANDFALL ALONG THE SOUTHEASTERN COAST OF CHINA BY TAU 
120. REGARDING INTENSITY, THE LENGTHY ERC HAS PROVEN TO BE A 
SIGNIFICANT INHIBITING FACTOR, PRECLUDING TY 17W FROM REACHING ITS 
INITIALLY PREDICTED INTENSITY. AT THIS POINT, ONCE THE ERC WRAPS UP, 
THE SYSTEM WILL HAVE MOVED INTO A LESS FAVORABLE ENVIRONMENT WHICH WILL
LIMIT ITS ABILITY TO REINTENSIFY POST-ERC. THE PRIMARY INHIBITOR GOING 
FORWARD WILL BE A LACK OF OUTFLOW, WHICH WILL BE CHOKED OFF BY THE 
PRESENCE OF A NEARBY UPPER-LEVEL ANTICYCLONE TO THE NORTH. AS THE 
SYSTEM BECOMES ISOLATED FROM AN OUTFLOW PERSPECTIVE, IT ALSO BECOMES 
COMPLETELY SURROUNDED BY DRY AIR, IN EFFECT COCOONING THE SYSTEM. 
INTENSITY IS FORECAST TO REMAIN RELATIVELY STEADY FOR THE FIRST 36 
HOURS, THEN BEGIN TO STEADILY WEAKEN THROUGH THE REMAINDER OF THE 
FORECAST. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EARLY 
PHASES OF THE FORECAST. CROSS-TRACK SPREAD INCREASES TO 165NM BY TAU 
72, WITH NAVGEM DIVERGING FROM THE REMAINDER OF THE GUIDANCE AND 
MARKING THE SOUTHERN OUTLIER, WHILE THE GFS AND AI-BASED MODELS MARK 
THE NORTHERN EDGE OF THE ENVELOPE. THROUGH TAU 72, ENSEMBLE MEMBER 
DISPERSION IS MINOR, AND THE ENSEMBLE MEAN TRACKERS ARE CONSISTENT WITH 
THE CONSENSUS MEAN. THE JTWC FORECAST THROUGH TAU 72 IS PLACED NEAR THE 
AI CONSENSUS WITH HIGH CONFIDENCE. AFTER TAU 72, CROSS-TRACK MODEL 
SPREAD INCREASES TO NEARLY 400NM, WITH THE GALWEM TRACK THIS SYSTEM 
WESTWARD INTO CHINA ALONG THE 28TH PARALLEL, WHILE GFS DIVES THE SYSTEM 
JUST WEST OF ISHIKAGIJIMA BEFORE MAKING LANDFALL ALONG THE EAST-CENTRAL 
COAST OF TAIWAN PRIOR TO TAU 120. THE REMAINDER OF THE GUIDANCE MEMBERS 
ARE DISPERSED BETWEEN THE TWO OUTLIERS. ENSEMBLE DISPERSION INCREASES 
SHARPLY AFTER TAU 72 AS WELL, WITH THE EXPERIMENTAL JTWC SUPER ENSEMBLE
DEPICTING MEMBERS EXTENDING FROM THE SOUTH COAST OF KOREA ALL THE WAY 
TO HAINAN, THOUGH THE MOST CONCENTRATED TRACK DENSITY IS FOCUSED ALONG 
THE OVERALL ENSEMBLE MEAN TRACK. THE JTWC FORECAST IS PLACED NEAR THE 
EXPERIMENTAL GOOGLE DEEPMIND TRACKER THROUGH TAU 120, WITH MEDIUM 
CONFIDENCE. INTENSITY GUIDANCE IS IN STRONG AGREEMENT DEPICTING A FLAT 
INTENSITY TREND THROUGH TAU 36 FOLLOWED BY STEADY WEAKENING THROUGH TAU 
120. 

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