WDPN31 PGTW 080900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YUN-YEUNG) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 32.6N 137.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 196 NM SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 12W HAS CLEARLY DECIDED TO DELAY ITS TRIP TO
JAPAN AND TAKE AN EXCURSION FURTHER OUT TO SEA. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED LOW
LEVEL CIRCULATION CENTER (LLCC) WHICH IS VERY SLOWLY DRIFTING OFF
TO THE EAST AFTER HAVING COME TO A STANDSTILL OVER THE PREVIOUS
6-12 HOURS. THE MSI ALSO SHOWS WHAT COULD BE A NASCENT WARM FRONTAL
BAND EXTENDING NORTHEASTWARD FROM THE NORTHERN PORTION OF THE LLCC.
SURFACE OBSERVATIONS FROM ACROSS THE REGION WOULD SUGGEST THE
PRESSURE FIELD IS INDEED ELONGATED ALONG A NORTHEAST AXIS AND A
CLEAR BOUNDARY EXISTS IN THE MSI WHERE STRATIFORM CLOUDS ARE
FORMING TO THE NORTH. DEEP CONVECTION IS SEEN FLARING ALONG A
CONVERGENCE LINE TO THE NORTHWEST OF THE CENTER BUT IS NOT
ORGANIZED AND REMAINS LINEAR IN NATURE. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC. THE
INITIAL INTENSITY IS HELD AT A GENEROUS 35 KNOTS BASED ON THE AIDT
AND SATCON ESTIMATES, THOUGH WHATEVER GALES MAY BE PRESENT ARE
PRIMARILY RESTRICTED TO A BAND BETWEEN THE CENTER AND THE COAST OF
HONSHU, CONSISTENT WITH AN EARLIER SCATTEROMETER PASS FROM 072230Z.
THE ENVIRONMENT REMAINS POSITIVELY ABYSMAL, WITH DRY AIR
BLANKETING THE SYSTEM, SOUTHERLY SHEAR OF 45 OR MORE KNOTS AND AN
ELONGATED AND RAGGED LLCC. AND AS NOTED YESTERDAY, THE SYSTEM
EXHIBITS HYBRID CHARACTERISTICS, WITH MODERATE WARM AND WEAK COLD
AIR ADVECTION, INTERACTION WITH A 200MB JET STREAK AND SIGNIFICANT
DRY AIR ENTRAINMENT, MARKING IT AS A SHALLOW, ASYMMETRIC WARM CORE
SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DRIFTING EASTWARD IN A WEAK STEERING
ENVIRONMENT, GENERALLY FOLLOWING THE ISENTROPIC BOUNDARY EXTENDING
FROM THE CENTER TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 080412Z
   CIMSS ADT: 31 KTS AT 080530Z

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: THE FORECAST TRACK HAS SHIFTED
SIGNIFICANTLY TO THE EAST AND IS MUCH SLOWER, RESULTING IN A MAJOR
SHIFT IN LANDFALL LOCATION, AS WELL AS DISSIPATION PRIOR TO
REACHING THE SEA OF JAPAN. 

FORECAST DISCUSSION: DUE TO THE RECENT, RATHER UNEXPECTED TRACK
MOTION, THE FORECAST TRACK HAS SHIFTED EAST AND SLOWED DOWN
SIGNIFICANTLY. THE MOST RECENT ANIMATED MSI SUGGESTS WE MAY ALREADY
BE SEEING THE BEGINNING OF A TURN TO THE NORTHEAST BUT ITS STILL
TOO EARLY TO TELL HOW SHARP THIS TURN MAY BE. THE OVERALL STEERING
PATTERN IS EXPECTED TO STRENGTHEN AS THE ANTICYCLONE TO THE EAST
BUILDS AND MOVES FURTHER INTO THE NORTH PACIFIC. AS THE LOW TO
MID-LEVEL RIDGE EXTENDS TOWARDS THE SOUTHWEST, IT WILL BLOCK ANY
FURTHER MOVEMENT OF TS 12W TO THE EAST, AND THE SYSTEM IS
FORECAST TO TURN TO THE NORTH-NORTHEAST BY TAU 12 AND THEN CONTINUE
ON THAT TRACK THROUGH THE FORECAST PERIOD. THE SYSTEM IS NO LONGER
EXPECTED TO INTENSIFY, AND IN FACT WILL STEADILY WEAKEN OVER THE
NEXT 24 HOURS AS IT APPROACHES THE SOUTHERN COAST OF HONSHU. SOME
ISOLATED POCKETS OF FUNNELING INDUCED GALE-FORCE WINDS ARE LIKELY
TO OCCUR IN THE CLIMATOLOGICALLY FAVORED AREAS, BUT OVERALL THE
SYSTEM WILL WEAKEN TO TROPICAL DEPRESSION STRENGTH WITHIN THE NEXT
12 HOURS. AFTER LANDFALL, THE SYSTEM WILL TRACK OVER THE RUGGED
TERRAIN OF THE JAPANESE ALPS AND DISSIPATE NO LATER THAN TAU 36. 

MODEL DISCUSSION: NORMALLY RELIABLE TRACK GUIDANCE HAS NOT
PERFORMED WELL AT ALL OVER THE PAST 24 HOURS AND CONTINUES THIS
TREND WITH THE MOST CURRENT RUN. THE MAJORITY OF THE GUIDANCE
CONTINUES TO INSIST THE SYSTEM SHOULD BE TRACKING NORTHWARD FROM
TAU 00 THROUGH AT LEAST TAU 24, WHICH CLEARLY IS NOT OCCURRING. THE
ONLY MODEL THAT SHOWS A NORTHEASTWARD TRACK IS THE GFS AND THE
SECOND INTERPOLATION OF THE ECMWF RUN. BOTH MODELS ARE TOO FAST,
AND SHOW THE SYSTEM TRACKING AT OVER 15 KNOTS OR MORE AFTER TAU 12.
JTWC GENERALLY FOLLOWS THE GFS AND ECMWF TRACK BUT AT A MUCH
SLOWER PACE. CONFIDENCE IS LOW PARTICULARLY IN LIGHT OF HOW POORLY
THE MODEL GUIDANCE HAS HANDLED THIS SYSTEM TO DATE. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT ON A RAPID WEAKENING TREND TO
DISSIPATION BY TAU 36. HOWEVER, THE HIGH UNCERTAINTY IN THE
ULTIMATE TRACK 12W WILL TAKE LEADS TO HIGH UNCERTAINTY AND LOW
CONFIDENCE IN THE INTENSITY FORECAST AS WELL. 

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