WDPN31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (MEKKHALA) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.3N 125.6E
   INITIAL INTENSITY: 125 KTS
   GEOGRAPHIC REFERENCE: 507 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
DEGRADED CONVECTIVE STRUCTURE WITH SOME EROSION OF THE CENTRAL
DENSE OVERCAST ON THE NORTHERN SIDE AND AN INCREASINGLY RAGGED,
COOLING EYE. THE POLEWARD VENTILATION ALOFT IS RESTRICTED DUE TO
NORTHERLY VERTICAL WIND SHEAR (VWS) CAUSED BY AN UPPER LEVEL RIDGE
OVER THE SOUTH CHINA SEA. THE 89 GHZ GMI IMAGE FROM 221709Z SHOWS A
SLIGHT TILT IN THE VORTEX AS A RESULT OF THE VWS. AFTER A PERIOD OF
EXTREMELY RAPID INTENSIFICATION (RI), TYPHOON 07W LIKELY PEAKED
AROUND 221200Z AT CLOSE TO SUPER TYPHOON INTENSITY. THE FORWARD
MOTION OF THE SYSTEM HAS SLOWED TO 5 KTS. ENVIRONMENTAL ANALYSIS
REVEALS MARGINALLY UNFAVORABLE CONDITIONS FOR DEVELOPMENT: ABUNDANT
DEEP LAYER MOISTURE OFFSET BY MODERATE VWS AND INCREASING POTENTIAL
FOR UPWELLING. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE RAGGED EYE FEATURE IN THE EIR IMAGERY. THE
INITIAL INTENSITY IS SET AT 125 KTS WITH HIGH CONFIDENCE BASED ON
THE UNANIMOUS T6.5 FROM PGTW, KNES, RJTD, AND RCTP.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.5 - 127 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 129 KTS AT 221900Z
   CIMSS ADT: 127 KTS AT 221900Z
   CIMSS AIDT: 123 KTS AT 221900Z
   CIMSS D-MINT: 121 KTS AT 221749Z
   CIMSS D-PRINT: 123 KTS AT 221900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: COLD WATER UPWELLING

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 07W IS IN A COMPETING STEERING
ENVIRONMENT AS IT ROUNDS AND APPROACHES A WEAKNESS IN THE STR. A
DEEP-LAYER RIDGE OVER THE SOUTH CHINA SEA HAS CAUSED MEKKHALA TO
SLOW DOWN. THIS RATE OF MOTION WILL CONTINUE UNTIL THE SYSTEM
REACHES THE STR AXIS AT TAU 72. ONCE POLEWARD OF THE RIDGE AXIS,
THE TYPHOON WILL ACCELERATE TOWARDS THE NORTHEAST AS IT BECOMES
EMBEDDED WITHIN THE MID-LATITUDE WESTERLIES AND UNDERGOES
EXTRATROPICAL TRANSITION. ENVIRONMENTAL CONDITIONS WILL ONLY WORSEN
AS 07W GAINS LATITUDE. AN UPPER LEVEL RIDGE CENTERED OVER CHINA IS
ALREADY EXERTING MODERATE NORTHERLY VWS, WHICH WILL INCREASE TO
25-35 KTS FROM THE EAST IN THE NEXT 36 HOURS. UPWELLING OF COOLER
OCEAN WATERS FROM BELOW IS BECOMING AN INCREASINGLY IMPORTANT
FACTOR DUE TO THE 5 KT MOVEMENT SPEED OF THE SYSTEM. THESE FACTORS
WILL INDUCE STEADY WEAKENING THROUGH TAU 72. AT TAU 96 AND 120,
MEKKHALA WILL GAIN STRONG DIVERGENCE ALOFT AS IT APPROACHES THE
RIGHT ENTRANCE QUADRANT OF A JET STREAK OVER NORTHERN HONSHU. THE
UPPER LEVEL SUPPORT WITH INCREASING BAROCLINICITY WILL MODERATE THE
RATE OF WEAKENING AT THE END OF THE FORECAST PERIOD, WITH THE
SYSTEM POTENTIALLY SKIRTING THE KANTO PLAIN WITH STORM-FORCE WINDS.

MODEL DISCUSSION: THE RELIABLE TRACK GUIDANCE IS IN GOOD OVERALL
AGREEMENT ON THE RECURVATURE MOTION OF TYPHOON 07W. SIGNIFICANT
DIFFERENCES ARISE IN THE ALONG-TRACK SPREAD BEYOND TAU 72. NAVGEM,
GALWEM, AND GFS ARE MUCH SLOWER THAN THE UKMET, HAFS-A, AND AI
MODELS IN ACCELERATING THE SYSTEM TOWARDS THE NORTHEAST BY AS MUCH
AS 350 NM AT TAU 72. THE AI MODELS TEND TO SHOW A STRONGER RECURVE,
KEEPING THE SYSTEM CENTER OFF THE COAST OF THE KANTO PLAIN BY 50-80
NM, WHILE THE GFS AND ECMWF MODELS SHOW LANDFALL. THE JTWC TRACK
FORECAST IS HEDGED CLOSER TO THE AI MODELS THROUGH TAU 72 WITH
MEDIUM CONFIDENCE AND THEN CLOSER TO THE GFS AND ECMWF AT TAU 96
AND TAU 120 WITH LOW CONFIDENCE. VIRTUALLY ALL OF THE INTENSITY
GUIDANCE DEPICTS STEADY WEAKENING THROUGH TAU 72, WHICH THE JTWC
INTENSITY FORECAST STRADDLES WITH MEDIUM CONFIDENCE. DIFFERENCES IN
TIMING BEYOND 72 HOURS WILL DICTATE THE AMOUNT OF UPPER LEVEL
SUPPORT ACCESSIBLE TO THE TYPHOON, AND THIS IS WHERE THE INTENSITY
GUIDANCE DIVERGES. AT TAU 72, THE GOOGLE DEEPMIND AND GFS MODELS
SHOW SOME STRENGTHENING, WHILE HAFS-A SHOWS RAPID WEAKENING. THE
INTENSITY FORECAST BEYOND 72 HOURS IS SET BETWEEN THESE DIVERGENT
SOLUTIONS WITH LOW CONFIDENCE.

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