Advisories

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 SLOW DOWN MARKEDLY 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 NO 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 BRIEF 
PERIOD OF REINTENSIFICATION FROM TAU 48 TO TAU 60 BEFORE CONTINUING TO 
WEAKEN, 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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