WDPN31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SAUDEL) WARNING NR 025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.9N 133.5E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 323 NM EAST-SOUTHEAST OF KADENA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 46 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
17W (SAUDEL) HAVING BECOME MUCH MORE IRREGULAR OVER THE PAST 6
HOURS WITH A CLEAR WEAKNESS IN THE NORTHWESTERN QUADRANT OF THE
EYEWALL AND A COOLING EYE. THERE APPEARS TO BE SOME DRY AIR
INTRUDING INTO THE VORTEX WITHIN THE WESTERN SEMICIRCLE AND
NORTHWESTERLY SHEAR IS STARTING TO INCREASE. A 240914Z RCM-1 SAR
PASS REVEALED A VMAX OF 100 KTS IN THE EASTERN PORTION OF THE
EYEWALL. THE SAR ALSO SHOWED THAT THE WIND FIELD HAS BECOME
SOMEWHAT ASYMMETRIC WITH THE STRONGEST WINDS LOCATED IN THE EASTERN
AND NORTHERN PORTIONS OF THE CIRCULATION. A 240934Z GMI 37 GHZ
MICROWAVE IMAGE CONFIRMED THAT THE INNER CORE HAS BECOME A BIT
DISORGANIZED WITH A FRAGMENTED MICROWAVE EYE FEATURE. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN
ANIMATED EIR AND EXTRAPOLATION FROM THE GMI MICROWAVE IMAGE. THE
INITIAL INTENSITY OF 100 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON A COMBINATION OF THE AFOREMENTIONED SAR DATA AND THE
INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS INDICATES
THAT 17W IS NOW IN A MARGINALLY FAVORABLE ENVIRONMENT CHARACTERIZED
BY STRONG RADIAL OUTFLOW ALOFT, 10-15 KTS NORTHWESTERLY SHEAR, DRY
AIR, AND WARM (28-29 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: 241123Z METOP-B ASCAT SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 104 KTS AT 241200Z
   CIMSS AIDT: 102 KTS AT 241200Z
   CIMSS D-MINT: 98 KTS AT 241130Z
   CIMSS D-PRINT: 107 KTS AT 241200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT FROM THE WEST

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: TY 17W IS FORECAST TO CONTINUE TRACKING
WEST-NORTHWESTWARD THROUGH TAU 36, PASSING JUST NORTH OF OKINAWA AT
AROUND TAU 30. NEAR TAU 36, 17W WILL APPROACH A WEAKNESS IN THE
STEERING RIDGE TO THE NORTH, CAUSING IT TO MARKEDLY SLOW DOWN AS
THE PRIMARY STEERING MECHANISM SHIFTS TO A SUBTROPICAL RIDGE (STR)
CENTERED OVER EASTERN CHINA. TRACK SPEEDS ARE EXPECTED TO REMAIN
SLOW THROUGH TAU 60 BEFORE THE STEERING GRADIENT BECOMES STRONGER.
AFTER TAU 60, THE SPEED OF ADVANCE OF 17W IS FORECAST TO BEGIN
INCREASING WITH A SOUTHWESTWARD TRAJECTORY AS THE SYSTEM TRACKS
ALONG THE SOUTHEASTERN PERIPHERY OF THE STR OVER CHINA THROUGH THE
REMAINDER OF THE FORECAST PERIOD. LANDFALL OVER EASTERN CHINA IS
CURRENTLY FORECAST TO OCCUR JUST BEFORE TAU 96. IN TERMS OF
INTENSITY, 17W IS FORECAST TO CONTINUE GRADUALLY WEAKENING UNDER
THE EFFECTS OF INCREASING NORTHWESTERLY SHEAR AND DRY AIR ENTRAINMENT.
ADDITIONALLY, THE UPPER-LEVEL TROUGH CURRENTLY TO THE WEST OF THE 
SYSTEM IS EXPECTED TO MOVE WESTWARD AND FILL, REDUCING OUTFLOW ALOFT. 
AT AROUND TAU 72, NORTHEASTERLY SHEAR WILL GREATLY INCREASE, INDUCED 
BY THE STRONG RIDGE OVER EASTERN CHINA CAUSING A MORE RAPID RATE OF 
WEAKENING AS THE SYSTEM APPROACHES THE COAST. AFTER LANDFALL, RUGGED 
TERRAIN INTERACTION WILL CAUSE THE VORTEX TO RAPIDLY WEAKEN WITH
DISSIPATION FORECAST TO OCCUR AROUND TAU 120, WELL NORTH OF HONG
KONG.

MODEL DISCUSSION: MODEL TRACK GUIDANCE IS IN VERY GOOD AGREEMENT
THROUGH TAU 72 WITH A CROSS-TRACK SPREAD OF ONLY 60 NM AT TAU 48
AND 140 NM AT TAU 72. NOTABLY, THE GFS HAS BECOME MUCH MORE IN LINE
WITH THE MAIN GROUPING OF TRACKERS, AND IS NOT LONGER DEPICTING THE
SHARP SOUTHWESTWARD TURN TOWARD TAIWAN. THE JTWC TRACK FORECAST IS
PLACED NEAR THE MULTI-MODEL CONSENSUS THROUGH TAU 72 AND THEN CLOSER 
TO THE EXPERIMENTAL GOOGLE DEEPMIND AND ECMWF ENSEMBLE MEAN THROUGH 
TAU 120. INTENSITY GUIDANCE GENERALLY AGREES ON STEADY WEAKENING 
THROUGHOUT THE ENTIRE FORECAST PERIOD. HAFS-A ONLY DIFFERS IN THAT IT 
SHOWS A BREIF PERIOD OF REINTENSIFICATION FROM TAU 48 TO TAU 60 BEFORE 
CONTINUING WEAKENING, THOUGH IT IS THE MOST EQUATORWARD TRACKER AFTER 
TAU 48. THE JTWC INTENSITY FORECAST IS PLACED NEAR THE CONSENSUS 
THROUGHOUT THE ENTIRE FORECAST PERIOD WITH OVERALL MEDIUM CONFIDENCE.


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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