WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YUN-YEUNG) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.6N 137.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 207 NM SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
QUASI-STATIONARY AND FULLY EXPOSED CIRCULATION THAT IS FULLY
BENEATH A MID LATITUDE TROUGH AND ASSOCIATED UPPER LEVEL JET.
RECENT 072126Z SSMIS 91GHZ MICROWAVE IMAGE DEPICTS TIGHTLY WRAPPING
LOW LEVEL CLOUD LINES FULLY DISSOCIATED FROM ANY DEEP CONVECTION
DISPLACED WELL TO THE NORTH. SURFACE OBSERVATIONS FROM HAMAMATSU
AND HACHIJOJIMA JAPAN, CONFIRM A LARGE, NORTH-SOUTH ELONGATED
CIRCULATION OF 30KT WINDS IS LOITERING JUST SOUTH OF HONSHU. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON MSI AND
SSMIS IMAGERY. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON DVORAK INTENSITY ESTIMATES GENERALLY
INDICATING 30-35KTS WHILE AUTOMATED INTENSITY ESTIMATES SUCH AS
CIMSS ADT, AIDT AND DPRINT INDICATE 38-41KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 39 KTS AT 072330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30+ KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TS 12W (YUN-YEUNG) HAS REMAINED GENERALLY
STATIONARY OVER THE PAST 6 HOURS. WITH VWS VALUES CLIMBING PAST
30KTS, THE MID-UPPER LEVEL STRUCTURES OF THE SYSTEM HAVE BEEN
EVISCERATED AND TRANSPORTED POLEWARD, LEAVING AN EXPOSED LOW LEVEL
CIRCULATION BEHIND. THE STEERING RIDGE TO THE EAST IS MUCH WEAKER
IN THE LOWER LEVELS, RESULTING IN THE RECENT QS PERIOD. OVER THE
NEXT 12 HOURS, THE STR TO THE EAST WILL PROPAGATED WESTWARD AND
COMBINED WITH THE SOUTHERLY WINDS AT THE SURFACE, 12W IS FORECAST
TO ONCE AGAIN REGAIN POLEWARD TRACK MOTION. HIGH VWS VALUES
COMBINED WITH DRY AIR ENTRAINMENT AND INCREASING LAND INTERACTION
WILL STEADILY WEAKEN THE SYSTEM AS IT APPROACHES LANDFALL BY TAU
12. AS THE SYSTEM MOVES OVER MAINLAND JAPAN, INTENSITIES WILL
CONTINUE TO FALL TO AROUND 25KTS BY TAU 24 AT WHICH TIME 12W WILL
BEGIN TO DISSIPATE. BY TAU 36, 12W WILL FULLY DISSIPATE IN THE SEA
OF JAPAN AS THE REMNANTS OF THE SYSTEM ROUND THE STR AXIS.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT WITH ALL
MEMBERS TAKING THE SAME GENERAL TRACK INTO AND OVER JAPAN AS THE
SYSTEM ROUNDS THE STR AXIS. BASED IN THE 170NM SPREAD IN SOLUTION BY
TAU 24, THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE.
RELIABLE MODEL INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH ALL
MEMBERS WEAKENING THE SYSTEM THROUGH THE FORECAST PERIOD. GFS,
ECMWF AND THEIR ENSEMBLE ALL DISSIPATE THE SYSTEM BY TAU 24, WHILE
THE BULK OF THE REMAINING MEMBERS MAINTAIN A WEAK TROPICAL
DEPRESSION THROUGH TAU 24 AND DISSIPATION THERE AFTER. FOR THIS
REASON THE JTWC INTENSITY FORECAST IS ALSO PLACED WITH MEDIUM
CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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