WDPN31 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 07W (MEKKHALA) WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.6N 124.7E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 448 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THE
LOW-LEVEL CIRCULATION CENTER (LLCC) OF 07W BECOMING PARTIALLY
EXPOSED IN THE NORTHERN SEMICIRCLE AS THE MID-UPPER-LEVEL
CIRCULATION IS SHEARED TOWARD THE SOUTHWEST. THE PRESENCE OF STRONG
NORTHEASTERLY VERTICAL WIND SHEAR (VWS) IS EVIDENT BY THE APPARENT
VORTEX TILT AND LACK OF DEEP CONVECTION IN THE NORTHERN SEMICIRCLE.
THAT SAID, THE LACK OF ANY RECENT MICROWAVE IMAGERY PRECLUDES A
MORE THOROUGH ANALYSIS OF THE DEGRADING STRUCTURE OF THE SYSTEM
ANIMATED WATER VAPOR IMAGERY REVEALS AN ABSENCE OF POLEWARD OUTFLOW
ALOFT, WHILE THE EQUATORWARD CHANNEL MAINTAINS MODERATE OUTFLOW
ALOFT. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
THE PARTIALLY EXPOSED LLCC IN ANIMATED EIR.  THE INITIAL INTENSITY
OF 100 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AGENCY
DVORAK FIXES OF T5.5-6.0. THE ENVIRONMENT IS CHARACTERIZED AS
UNFAVORABLE, WITH HIGH (25-30 KTS) VWS AND ENHANCED UPWELLING OF
COOLER WATER AS A RESULT OF THE SLOW STORM MOTION.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 90 KTS AT 231200Z
   CIMSS AIDT: 80 KTS AT 231200Z
   CIMSS D-PRINT: 84 KTS AT 231200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 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: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON (TY) 07W (MEKKHALA) HAS TURNED TO A
MORE NORTHWARD TRACK IN THE PAST 6 HOURS AS IT APPROACHES THE AXIS
OF THE STEERING STR CENTERED TO THE NORTHEAST. THE TRACK IS
FORECAST TO MAINTAIN A PRIMARILY NORTHWARD COMPONENT OVER THE NEXT
36 HOURS AS THE SYSTEM CONTINUES AROUND THE RIDGE AXIS, THEN TURN
NORTHEASTWARD WITH A SLIGHTLY FASTER TRACK SPEED AS IT APPROACHES
OKINAWA. THE CPA TO KADENA AB IS EXPECTED AT 260100Z AS THE CENTER
OF TY MEKKHALA TRACKS ALONG THE NORTHWEST COAST OF OKINAWA. AROUND
TAU 72, THE SYSTEM IS FORECAST TO ACCELERATE RAPIDLY ON A
NORTHEASTWARD TRACK AND SKIRT ALONG THE SOUTHEASTERN COAST OF
HONSHU, PASSING JUST SOUTH OF TOKYO NEAR TAU 96. STEADY WEAKENING
IS FORECAST THROUGH TAU 48 AS THE HIGH VWS ENVIRONMENT PERSISTS AND
TY 07W MOVES OVER GRADUALLY COOLER SST. AFTER TAU 48 THE VWS IS
EXPECTED TO DECREASE TO MORE FAVORABLE LEVELS WHILE POLEWARD
OUTFLOW GETS A BOOST FROM A JET ENTRANCE REGION AS MEKKHALA
APPROACHES THE MIDLATITUDE WESTERLIES. THIS SHOULD ALLOW THE SYSTEM
TO MAINTAIN STRONG TROPICAL STORM FORCE WINDS AS IT UNDERGOES
EXTRATROPICAL TRANSITION BEGINNING BY TAU 96, COMPLETING THE
TRANSITION BY TAU 120.  

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM AS THE SLOWEST AND
EASTERNMOST SOLUTION, MODEL TRACK GUIDANCE IS IN OVERALL GOOD
AGREEMENT WITH THE RECURVING TRACK OF 07W THROUGH TAU 60, WITH A
CROSS-TRACK SPREAD OF 55 NM. AFTER TAU 60, SOME UNCERTAINTY ABOUT
THE ACCELERATING TRACK SPEED AND THE EXTRATROPICAL TRANSITION
SCENARIO RESULT IN A SIGNIFICANT ALONG-TRACK SPREAD OF 630 NM. THE
ECMWF DETERMINISTIC MODEL IS THE FASTEST SOLUTION IN THE SPREAD
WHILE GALWEM IS THE SLOWEST, ALTHOUGH THEY ARE NOT SIGNIFICANT
OUTLIERS AS THE REMAINDER OF GUIDANCE FALLS BETWEEN THEM WITH
LITTLE CONSENSUS. THE JTWC TRACK FORECAST IS PLACED NEAR THE
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE THROUGH TAU 72 AND
MEDIUM CONFIDENCE THEREAFTER. AS FOR INTENSITY, HAFS-A CONTINUES TO
BE A SIGNIFICANT OUTLIER, SUGGESTING RAPID WEAKENING THROUGHOUT THE
FORECAST PERIOD. CONVERSELY, HWRF AND GFS SUGGEST A PERIOD OF
REINTENSIFICATION AFTER TAU 60, MAKING THEM OUTLIERS ON THE HIGHER
SIDE. THE REMAINDER OF GUIDANCE REMAINS WITHIN A 10-15KT ENVELOPE
THROUGHOUT THE FORECAST PERIOD. THE JTWC INTENSITY FORECAST IS
PLACED NEAR THE MEAN OF THE LATTER GROUPING WITH HIGH CONFIDENCE
THROUGH TAU 72 AND MEDIUM CONFIDENCE THEREAFTER. 

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