WDPN31 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YUN-YEUNG) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.7N 136.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 375 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) DISPLACED WELL NORTH OF
THE PRIMARY CONVECTIVE CELLS. A 070021Z GMI 89GHZ COLOR COMPOSITE
MICROWAVE IMAGE SHOWS A FULLY EXPOSED 12W AND THE REMNANTS OF 11W
MERGING WITH THE ITS WESTERN PERIPHERY. A 070105Z ASCAT-B
SCATTEROMETRY PASS SHOWS AN ASYMMETRIC DESERET CIRCULATION OF
15-20KT WINDS WITH A LARGE FIELD OF 35-40KT WINDS DOMINATING THE
SOUTHEASTERN QUADRANT. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON MSI AND GMI IMAGERY. THE INITIAL INTENSITY OF
40 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON SCATTEROMETRY DATA
AND DVORAK INTENSITY ESTIMATES INDICATING A RANGE OF 30-45KTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 34 KTS AT 062340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE STR TO THE EAST HAS CONTINUED TO
BUILD OVER EACH MODEL RUN, PUSHING NUMERICAL MODEL OUTPUT FURTHER
WESTWARD. WHILE THE JTWC FORECAST PHILOSOPHY REMAINS UNCHANGED, THE
JTWC FORECAST TRACK IS NOW INDICATING A WESTWARD APPROACH AND CPA
TO YOKOSUKA. 

FORECAST DISCUSSION: TS 12W (YUN-YEUNG) IS FORECAST TO CONTINUE
GENERALLY NORTH-NORTHEASTWARD UNDER THE STEERING INFLUENCE OF THE
STR TO THE EAST. OVER THE NEXT 12 HOURS, 12W WILL MOVE UNDER THE
UPPER LEVEL TROUGH WHICH IS SET UP OVER JAPAN, THE ASSOCIATED JET
MAX WILL PROVIDE VIGOROUS UPPER LEVEL OUTFLOW, WHILE AT THE SAME
TIME RATCHETING UP VERTICAL WIND SHEAR (VWS) VALUES. AFTER REACHING
A PEAK INTENSITY OF 45KTS AND POSSIBLY HIGHER BY TAU 12, DRY AIR
ENTRAINMENT AND VWS WILL BEGIN TO GRADUALLY WEAKEN THE SYSTEM AS IT
APPROACHES THE SOUTHERN COAST OF HONSHU. AS PREVIOUSLY MENTIONED,
THE STR TO THE EAST OF THE SYSTEM HAS CONTINUED TO BUILD AND NEAR
TAU 24 ACTUALLY REORIENTS, FORCING 12W ASHORE GENERALLY WESTWARD OF
YOKOSUKA, JAPAN. AS THE SYSTEM TRACK OVER JAPAN, IT WILL CONTINUE
TO WEAKEN TO AROUND 25KTS BY TAU 48 AND BY TAU 72, SHORTLY AFTER
REENTERING THE WESTERN PACIFIC, 12W WILL FULLY DISSIPATE.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT THROUGH
TAU 24 WITH ALL MEMBERS CLOSELY FOLLOWING THE JTWC FORECAST TRACK.
AFTER TAU 24, CROSS TRACK SPREADING INCREASES DRAMATICALLY WITH A
FEW MEMBERS ACTUALLY TAKING THE SYSTEM BRIEFLY INTO THE SEA OF
JAPAN, BEFORE ROUNDING THE STR AXIS AND PROCEEDING NORTHEASTWARD
AGAIN. BECAUSE OF THIS SPREADING AFTER TAU 24, THE JTWC FORECAST
TRACK IS PLACED WITH OVERALL MEDIUM CONFIDENCE. RELIABLE MODEL
INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH ALL MEMBERS EXCEPT FOR
DECAY-SHIPS INDICATING CONTINUED INTENSIFICATION THROUGH TAU 12,
AFTER WHICH WEAKENING THROUGH THE REMAINING FORECAST PERIOD. HAFS-A
IS ONLY MEMBERS THAT INTENSIFIES THE SYSTEM BEYOND 50KTS AND YET IS
ONE OF THE QUICKEST MEMBER TO DISSIPATE THE SYSTEM. DESPITE HAFS-A,
THE JTWC INTENSITY FORECAST IS PLACED WITH OVERALL MEDIUM
CONFIDENCE.

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