WDPN31 PGTW 232100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (MEKKHALA) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.2N 124.8E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 412 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON 07W HAS RAPIDLY WEAKENED OVER THE PAST 24 HOURS. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY NO LONGER DEPICTS AN EYE,
AND THE NORTHERN PERIPHERY OF THE LOW LEVEL CIRCULATION (LLCC) IS
PROGRESSIVELY BECOMING MORE EXPOSED. STRONG NORTHEASTERLY VERTICAL
WIND SHEAR (VWS) OF 25-30 KTS HAS ERODED THE CENTRAL DENSE OVERCAST
AND INCREASINGLY TILTED THE VORTEX. MEKKHALA IS MOVING SLOWLY
TOWARDS THE NORTH AT 4-6 KTS, WHICH HAS LIKELY INDUCED UPWELLING OF
COOLER WATERS. THE UPWELLING AND HIGH VWS CONSTITUTE AN ENVIRONMENT
THAT IS HOSTILE FOR DEVELOPMENT. A 230951Z SENTINEL-1D SAR PASS
ESTIMATED MAXIMUM SUSTAINED WINDS OF 95 KTS. SINCE THEN, THE STORM
STRUCTURE HAS CONTINUED TO DEGRADE. THE INITIAL POSITION IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE LLCC BEING PARTIALLY
EXPOSED. THE INITIAL INTENSITY IS LOWERED TO 85 KTS WITH MEDIUM
CONFIDENCE BASED ON THE LOWER END OF THE T5.0-5.5 SUBJECTIVE DVORAK
ESTIMATES AND IS CLOSEST TO SATCON FROM CIMSS.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 88 KTS AT 231900Z
   CIMSS ADT: 72 KTS AT 231900Z
   CIMSS AIDT: 67 KTS AT 231900Z
   CIMSS D-MINT: 76 KTS AT 231729Z
   CIMSS D-PRINT: 62 KTS AT 231830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: UPWELLING OF COOLER WATERS

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE TRACK HAS SHIFTED WESTWARD AND
FASTER THROUGH TAU 72.

FORECAST DISCUSSION: THE TYPHOON WILL CONTINUE TO SLOWLY MOVE
NORTHWARD AS IT APPROACHES A WEAKNESS IN THE DEEP-LAYER STR. FROM
TAU 24 TO TAU 36, THE SYSTEM WILL TURN TOWARDS THE NORTHEAST AS THE
RIDGE SHIFTS EASTWARD AND MID-LATITUDE WESTERLIES EXERT A STRONGER
STEERING INFLUENCE. 07W WILL ACCELERATE NORTHEASTWARD, UNDERGO
EXTRATROPICAL TRANSITION AT TAU 96, AND BECOME FULLY EXTRATROPICAL
BY TAU 120. MEKKHALA WILL CONTINUE TO STEADILY WEAKEN FOR THE FIRST
24 HOURS DUE TO HIGH VWS AND UPWELLING. BY TAU 36, THE TYPHOON WILL
ENCOUNTER COOLER 25-26 DEGREE CELSIUS WATERS IN A MUCH LOWER SHEAR
ENVIRONMENT, AND POLEWARD OUTFLOW WILL GREATLY IMPROVE. THE
CIRCULATION WILL COME INTO PHASE WITH A POTENT 130-KT JET STREAK
OVER NORTHERN HONSHU. THIS INTERACTION WILL SIGNIFICANTLY ENHANCE
DIVERGENCE ALOFT AND HELP MAINTAIN INTENSITY THROUGH TAU 72. A
FASTER RATE OF WEAKENING WILL COMMENCE AT TAU 96 WHEN 07W LOSES THE
UPPER LEVEL SUPPORT AND IS ABSORBED INTO A FRONTAL SYSTEM NEAR THE
KURIL ISLANDS BY TAU 120.

MODEL DISCUSSION: MODELS REMAIN IN TIGHT AGREEMENT THROUGH TAU 48.
THE UNCERTAINTY ENVELOPE STILL ENCOMPASSES THE SOUTHERN COAST OF
HONSHU FROM TAU 60 TO TAU 96 WITH SIGNIFICANT ALONG-TRACK SPREAD.
MODELS HAVE GENERALLY SHIFTED FASTER AND WESTWARD THIS CYCLE, WITH
THE ECMWF AND HAFS-A NOW BEING THE WESTERNMOST OUTLIERS AND THE
FASTEST. THE JTWC FORECAST TRACK HAS SHIFTED SLIGHTLY WESTWARD AND
FASTER TO ACCOUNT FOR THIS DEVELOPMENT AND IS NEARLY CENTERED
WITHIN THE TIGHTEST GROUPING OF MODELS WITH MEDIUM CONFIDENCE.
FUTURE ADJUSTMENTS TO THE WEST AND TO THE MOVEMENT SPEED MAY BE
NECESSARY IN SUBSEQUENT WARNINGS IF TRENDS CONTINUE. CONSEQUENTLY,
THE CPA FOR OKINAWA HAS SHIFTED EARLIER. THE INTENSITY AIDS SHOW
STEADY TO RAPID WEAKENING FOR THE FIRST 24-36 HOURS. THE JTWC
INTENSITY FORECAST IS NOT AS AGGRESSIVE AS HAFS-A OR THE
EXPERIMENTAL GOOGLE DEEPMIND MODELS IN WEAKENING THE SYSTEM AND IS
INSTEAD HEDGED TOWARDS GFS. MODELS SHOW A PAUSE IN WEAKENING
BETWEEN TAU 48 AND TAU 72 AND RESUMES WEAKENING TOWARDS THE END OF
THE PERIOD. THE JTWC FORECAST FOLLOWS THE OVERALL INTENSITY TREND
OUT TO TAU 120 WITH MEDIUM CONFIDENCE.

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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