Advisories

WDPN31 PGTW 230300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.0N 142.3E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 861 NM EAST-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PINHOLE
EYE FEATURE, THOUGH THE EYE IS SLIGHTLY LARGER IN BOTH THE ENHANCED
INFRARED (EIR) AND RECENT MICROWAVE IMAGERY. THE MSI SHOWS THE
SMALL EYE SURROUNDED BY STRONG VORTICAL HOT TOWERS (VHTS) RAPIDLY
DEVELOPING ALONG THE WESTERN FLANK OF THE EYE AND WRAPPING UPSHEAR
TO THE EASTERN SIDE. HOWEVER, BEYOND THE DEVELOPING EYEWALL LIES AN
OBVIOUS MOAT, DENOTING A WEDGE OF DRY AIR WHICH HAS WRAPPED ITS WAY
AROUND THE INNER CORE, AS PART OF THE ONGOING EYEWALL REPLACEMENT
CYCLE (ERC). A 222348Z GMI COLOR-ENHANCED 89GHZ IMAGE DEPICTS A
FRAGMENTED INNER EYEWALL, OPEN ACROSS THE NORTHERN SEMICIRCLE, WITH
A VERY WELL-DEFINED MOAT WRAPPING COUNTER-CLOCKWISE FROM SOUTHEAST
TO WEST OF THE MICROWAVE EYE FEATURE, WITH A SECONDARY EYEWALL
FORMING OUTBOARD OF THE MOAT. AS THE ERC CONTINUES TO EVOLVE, IT
WOULD BE EXPECTED THAT THE EYE WOULD STEADILY ENLARGE AS IT CLEARS
OUT, BUT THE MSI TELLS THE OPPOSITE STORY, WITH VHTS REDEVELOPING
ALONG THE INNER EYEWALL AND A NEW PINHOLE TYPE EYE TAKING SHAPE.
WHETHER THE DRY AIR CAN BE MIXED OUT AND HOW LONG THIS PROCESS
TAKES WILL DETERMINE THE FATE OF TY 17W IN THE NEAR-TERM. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EYE
FEATURE IN THE MSI AND EXTRAPOLATED GMI IMAGE. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF
THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE OVERALL, WITH THE WARM SSTS,
HIGH (100 KJ PER CM2) OHC AND STRONG OUTFLOW ALOFT OFFSET BY THE
ONGOING ERC AND ASSOCIATED DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 112 KTS AT 222300Z
   CIMSS ADT: 112 KTS AT 230000Z
   CIMSS AIDT: 105 KTS AT 230000Z
   CIMSS D-MINT: 112 KTS AT 222250Z
   CIMSS D-PRINT: 112 KTS AT 230000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: NORTHWESTWARD OUTFLOW CHANNEL; 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 A EXPANSIVE
SUBTROPICAL RIDGE (STR) WHICH EXTENDS FROM SOUTHERN JAPAN TO THE
NORTHWEST PACIFIC EAST OF IWO TO. NO SIGNIFICANT CHANGE IN THE
TRAJECTORY IS EXPECTED FOR THE NEXT 60 HOURS, AS THE STR REMAINS
FIRMLY ENTRENCHED. AROUND TAU 48, THE GLOBAL MODELS AGREE THAT THE
RIDGE WILL BEGIN TO REORIENT TO A FLATTER, MORE EAST-WEST
ORIENTATION, THOUGH NO SIGNIFICANT CHANGES IN POSITION OR STRENGTH
ARE EXPECTED. BEGINNING AROUND TAU 60 HOWEVER, THE GLOBAL MODELS
BEGIN TO DIVERGE, THOUGH NOT AS MUCH AS SIX HOURS, ON THE STRENGTH
AND IMPACT OF AN UPPER-LEVEL TROUGH MOVING IN FROM THE NORTHWEST.
THE GFS CONTINUES TO SHOW A STRONGER, DEEPER TROUGH WHICH INDUCES A
BREAK IN THE STR OVER SOUTH KOREA, RESULTING IN A SIGNIFICANT
SLOWDOWN AND SLIGHTLY BOWED TRACK FOR TY 17W AS IT MOVES ACROSS THE
RYUKYU ISLANDS BEFORE TURNING SOUTHWEST ALONG THE EASTERN FLANK OF
A BUILDING STR OVER CHINA AND ULTIMATELY IMPACTING NORTHEASTERN
TAIWAN. THE ECMWF ON THE OTHER HAND DEPICTS A MUCH WEAKER TROUGH
ALOFT, WHICH HAS MINIMAL IMPACT ON THE STR, LEADING TO A MUCH
FASTER, FURTHER SOUTH TRAJECTORY WHICH ALSO ULTIMATELY IMPACTS
NORTHEASTERN TAIWAN AFTER TURNING SOUTHWEST ALONG THE EASTERN FLANK
OF THE STR OVER CHINA. THE JTWC FORECAST CALLS FOR THE SYSTEM TO
SLOW DOWN SIGNIFICANTLY AS IT APPROACHES OKINAWA, REACHING ITS
SLOWEST SPEED JUST AFTER PASSING THE RYUKYUS, THEN ACCELERATING
SOUTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD.
REGARDING INTENSITY, THE ERC SHOULD WRAP UP WITHIN THE NEXT 12
HOURS, AND CONDITIONS WILL REMAIN FAVORABLE FOR ABOUT 24 HOURS
AFTER THAT POINT, ALLOWING TY 17W TO REINTENSIFY UP TO A PEAK OF
120 KNOTS. THE ONSET OF INCREASED SHEAR, DECREASING OUTFLOW ALOFT
AND DECREASING OHC WILL STEADILY WEAKEN TY 17W AFTER TAU 48 THROUGH
THE END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
72, WITH CROSS-TRACK SPREAD INCREASING TO 150NM BETWEEN ECMWF ON
THE SOUTHERN EDGE OF THE ENVELOPE AND GFS, GEFS, AND THE AI MODELS
ON THE NORTHERN FRINGE. ENSEMBLE GUIDANCE IS ALSO IN GOOD AGREEMENT
THROUGH TAU 72, WITH A MEMBER DISPERSION ENVELOPE ROUGHLY
ENCOMPASSING THE CENTRAL RYUKYU ISLANDS. THE JTWC FORECAST IS
PLACED NEAR THE GFS SOLUTION THROUGH TAU 72, WITH HIGH CONFIDENCE.
IN THE LONG-RANGE FORECAST, BOTH THE TRADITIONAL TRACK CONSENSUS
AND THE ENSEMBLES SHOW INCREASED UNCERTAINTY. WHILE CROSS-TRACK
SPREAD REMAINS CONSISTENT, ALONG-TRACK SPREAD INCREASES SHARPLY
AFTER TAU 72, WITH THE ECMWF CONTINUING TO BE THE FASTEST MODEL,
THOUGH GFS IS NOW CATCHING UP QUICKLY. BOTH NOW DEPICT LANDFALL BY
TAU 120 OVER NORTHEASTERN TAIWAN, WHILE THE CONSENSUS AND JGSM
DEPICT LANDFALL IN SOUTHEASTERN CHINA. THE REMAINDER OF THE
GUIDANCE, PARTICULARLY THE AI MODELS, LAG FAR BEHIND. ENSEMBLE
MEMBER DISPERSION ALSO INCREASES SHARPLY, RESULTING IN INCREASED
UNCERTAINTY IN THE LONG-RANGE FORECAST. INTENSITY GUIDANCE HAS
SHIFTED SIGNIFICANTLY WEAKER SINCE THE PREVIOUS RUN. THE ONLY MODEL
SHOWING ANY INTENSIFICATION NOW IS THE CTCX, WHICH PEAKS OUT AT 120
KNOTS AT TAU 24. THE JTWC FORECAST IS PLACED ON TOP OF THE CTCX
TRACKER TO TAU 36, THEN REJOINS THE CLUSTER OF MODELS THROUGH THE
REMAINDER OF THE FORECAST PERIOD. 

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