WDPN31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (MEKKHALA) WARNING NR 
035//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.7N 135.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 249 NM SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 07W (MEKKHALA) WITH AN INCREASINGLY ELONGATED, PARTIALLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). CONVECTION CONTINUES
TO BE DISPLACED TO THE EAST OF THE ASSESSED CENTER DUE TO THE
INFLUENCE OF STRONG WESTERLY VERTICAL WIND SHEAR ACTING ON THE
SYSTEM. A 270430Z AMSR2 WIND SPEED IMAGE REVEALED WINDS OF 35-40
KTS WITHIN A RELATIVELY CONVECTION-FREE AREA IN THE SOUTHERN 
PERIPHERY. GALE-FORCE WINDS ARE ANALYZED TO BE CONFINED TO THE 
SOUTHWESTERLY WINDS IN THE SOUTHERN SEMICIRCLE OF THE CIRCULATION.
THE INITIAL POSITION IS BASED ON THE ANIMATED MSI AND IS PLACED WITH 
LOW CONFIDENCE DUE TO THE STRETCHED LLCC AND HIGH TRANSLATION SPEED. 
THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH MEDIUM CONFIDENCE 
BASED ON THE AFOREMENTIONED AMSR2 IMAGE AND EARLIER SCATTEROMETER 
DATA. ENVIRONMENTAL ANALYSIS INDICATES THAT 07W IS IN A MARGINAL 
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT GREATLY 
OFFSET BY HIGH (25-30 KTS) VERTICAL WIND SHEAR, DRY AIR ENTRAINMENT, 
AND COOL (24-25 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR)

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS SATCON: 41 KTS AT 270610Z
   CIMSS ADT: 35 KTS AT 270610Z
   CIMSS AIDT: 39 KTS AT 270610Z
   CIMSS D-MINT: 36 KTS AT 270613Z
   CIMSS D-PRINT: 34 KTS AT 270610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 24-25 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 07W (MEKKHALA) IS FORECAST TO ACCELERATE
EAST-NORTHEASTWARD, ALONG THE NORTHERN PERIPHERY OF THE STR THROUGH
TAU 24. THE SYSTEM IS EXPECTED TO REMAIN OFF THE COAST OF HONSHU AS
IT ZIPS BY WITHIN THE NEXT 12 HOURS. EXTRATROPICAL TRANSITION (ETT)
IS CURRENTLY ONGOING AND IS EXPECTED TO COMPLETE BY TAU 24 AS THE
SYSTEM BECOMES ENVELOPED BY A LARGE FRONTAL SYSTEM FORMING SOUTH OF
THE KAMCHATKA PENINSULA. IN TERMS OF INTENSITY, 07W IS FORECAST TO
MAINTAIN ITS CURRENT INTENSITY OVER THE NEXT 12 HOURS DUE TO THE 
STRONG OUTFLOW AND BAROCLINIC FORCING. THE STRONGEST WINDS ARE 
EXPECTED TO REMAIN WITHIN THE SOUTHERN SEMICIRCLE, OFF THE COAST,
THROUGHOUT THE TRANSITION INTO AN EXTRATROPICAL CYCLONE. AROUND THE
TIME 07W COMPLETES ETT, THE INTENSITY IS FORECAST TO SLIGHTLY WEAKEN 
DUE TO THE INTERACTION WITH WIND FIELD OF THE LARGER FRONTAL SYSTEM 
AND VERY HIGH WESTERLY SHEAR. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD AGREEMENT 
THROUGHOUT THE SHORT FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF ONLY 
55 NM AND AN ALONG-TRACK SPREAD OF 145 NM AT TAU 24. GALWEM IS THE 
ONLY NOTICEABLE OUTLIER, SUGGESTING A SLOWER TRANSLATION SPEED THAN 
THE REST OF GUIDANCE. THE JTWC TRACK FORECAST IS PLACED CLOSE TO THE 
MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE 
GENERALLY AGREES ON LITTLE TO NO WEAKENING THROUGH TAU 12 FOLLOWED BY 
A SLIGHTLY FASTER RATE OF WEAKENING THEREAFTER. AS A RESULT, THE JTWC 
INTENSITY FORECAST IS ALSO PLACED NEAR THE CONSENSUS WITH HIGH 
CONFIDENCE.

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