WDPN31 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (MEKKHALA) WARNING NR 
033//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.6N 131.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 549 NM SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION
FLARING UP ALONG THE OUTER PERIPHERY. THE CONVECTIVE ACTIVITY IS
BEGINNING TO EXPAND DUE TO INCREASING DIVERGENCE ALOFT.
ENVIRONMENTAL ANALYSIS INDICATES UNFAVORABLE CONDITIONS OF MARGINAL
SEA SURFACE TEMPERATURE (SST) OF 26 DEGREES CELSIUS, DRY AIR
INTRUSION FROM THE EAST, AND MODERATE TO HIGH VERTICAL WIND SHEAR
(VWS), OFFSET BY MODERATE TO STRONG POLEWARD OUTFLOW. BOTH THE
261209Z ASCAT-C AND 261522Z OSCAT-3 PASSES REVEAL 30-35 KT WINDS
CONFINED TO THE SOUTHEAST QUADRANT AND SUGGEST THAT THE WIND FIELD
IS BECOMING LESS SYMMETRIC. THEREFORE, THE INITIAL INTENSITY
REMAINS AT 35 KTS WITH HIGH CONFIDENCE. THE INITIAL POSITION IS
ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED CENTER ON
ANIMATED SHORTWAVE IR IMAGERY.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE NORTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE AND DEEP-LAYER WESTERLIES

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 35 KTS AT 261800Z
   CIMSS ADT: 25 KTS AT 261800Z
   CIMSS AIDT: 33 KTS AT 261800Z
   CIMSS D-MINT: 30 KTS AT 261717Z
   CIMSS D-PRINT: 29 KTS AT 261800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: COMPARED TO SIX HOURS AGO, THE NORTHEAST
MOTION INCREASED FROM 11 KTS TO 21 KTS. TROPICAL STORM 07W, WHICH
IS UNDERGOING EXTRATROPICAL TRANSITION, WILL CONTINUE TO ACCELERATE
TO THE NORTHEAST UNDER THE STRENGTHENING INFLUENCE OF DEEP-LAYER
SOUTHWESTERLY FLOW. THE CENTER OF THE SYSTEM WILL TRACK SOUTH OF
THE SOUTHERN COAST OF HONSHU THROUGH TAU 36, BEFORE MERGING WITH A
FRONTAL SYSTEM OVER THE KURIL ISLANDS. AS MEKKHALA PULLS
NORTHEASTWARD, IT WILL GAIN A POTENT, POLEWARD OUTFLOW CHANNEL AS
CIRCULATION PHASES WITH A JET STREAK OVER NORTHERN HONSHU.
THEREFORE, THE FORECAST CALLS FOR SLIGHT INTENSIFICATION AT TAU 12.
WEAKENING WILL OCCUR AT TAU 36 WHEN THE SYSTEM LOSES THE UPPER
LEVEL SUPPORT.

MODEL DISCUSSION: MODELS ARE IN VERY TIGHT AGREEMENT THROUGH TAU 36
WITH A CROSS-TRACK SPREAD OF 50 NM, LEADING TO HIGH CONFIDENCE IN
THE JTWC FORECAST TRACK. JGSM IS THE SOUTHERMOST MODEL, WHILE THE
UKMET AND GALWEM MODELS REPRESENT THE NORTHERMOST SIDE OF THE
ENVELOPE. ALL OF THE MODELS KEEP THE CENTER OF THE CIRCULATION
OFFSHORE OF HONSHU. THE TRACK FORECAST IS SET NEAR THE CENTER OF
THE GUIDANCE ENVELOPE AND IS CLOSEST TO THE GFS AND ECMWF MODELS.
THE RELIABLE INTENSITY AIDS, WHICH INCLUDE GFS, HAFS-A, AND
COAMPS-TC, SHOW SLIGHT INTENSIFICATION AT TAU 12. THE JTWC CONCURS
WITH THIS PREDICTION WITH HIGH CONFIDENCE, BRINGING MEKKHALA TO 40
KTS AT TAU 12 AND TAU 24. THESE MODELS SHOW A SUSTAINED DECLINE IN
INTENSITY BY TAU 36, WITH HAFS-A SHOWING MORE RAPID WEAKENING THAN
GFS. THE JTWC FORECAST INTENSITY IS HEDGED TOWARDS THE GFS SOLUTION
AT TAU 36.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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