WDPN31 PGTW 051500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W (YUN-YEUNG) 
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.9N 132.4E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 836 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A LARGE AREA OF 
PERSISTENT DEEP CONVECTION OBSCURING THE LOW-LEVEL CIRCULATION CENTER 
(LLCC). CONSEQUENTLY, THERE IS SOME UNCERTAINTY IN THE INITIAL 
POSITION WITH AGENCY DVORAK FIXES POSITIONED TOO FAR SOUTH UNDER THE 
DEEP CONVECTION. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE 
BASED ON A 050925Z SSMIS 91 GHZ MICROWAVE IMAGE, WHICH REVEALS A 
CURVED CONVECTIVE BAND OVER THE SOUTHERN SEMICIRCLE, AND A 051215Z 
PARTIAL ASCAT-C IMAGE. BOTH THESE IMAGES PROVIDE SOLID EVIDENCE THAT 
THE LLCC IS LOCATED ALONG THE NORTHERN EDGE OF THE DEEP CONVECTION 
NEAR 23N LATITUDE. THE ASCAT-C 25 KM IMAGE INDICATES A SWATH OF 20-25 
KNOT WESTERLY WINDS UNDER THE DEEP CONVECTION. THIS DATA, ALONG WITH 
THE PGTW AND KNES DVORAK ESTIMATES, SUPPORTS THE INITIAL INTENSITY 
ESTIMATE OF 25 KNOTS WITH MEDIUM CONFIDENCE.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) 
POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 12W IS FORECAST TO
TRACK NORTHEASTWARD TO NORTH-NORTHEASTWARD ALONG THE WESTERN
PERIPHERY OF THE STR THROUGH TAU 96 THEN TURN SHARPLY EASTWARD AND
SLOW AS IT ROUNDS THE STR AXIS. THE STR IS FORECAST TO REMAIN
ENTRENCHED TO THE EAST THROUGH MOST OF 12W'S LIFECYCLE AND THE
RAPID PASSAGE OF A MIDLATITUDE SHORTWAVE TROUGH OVER NORTHERN JAPAN
NEAR DAY TWO IS UNLIKELY TO SIGNIFICANTLY AFFECT THE STR OR
INITIATE A TYPICAL RECURVE SCENARIO. ADDITIONALLY, THE BAROCLINIC
ZONE IS WELL NORTH OF 40 NORTH THUS THE SYSTEM IS NOT EXPECTED TO
UNDERGO EXTRA-TROPICAL TRANSITION. THE SHORTWAVE TROUGH, HOWEVER,
SHOULD BOOST POLEWARD OUTFLOW THROUGH TAU 48 WITH A PEAK INTENSITY
OF 55 KNOTS ANTICIPATED AT TAU 48. AFTER TAU 72, ENVIRONMENTAL
CONDITIONS SHOULD DEGRADE WITH DRY AIR ENTRAINMENT, COOLING SST
VALUES AND INCREASING VERTICAL WIND SHEAR LEADING TO A GRADUAL
WEAKENING TREND THROUGH TAU 120. EVENTUALLY TD 12W WILL DISSIPATE
NEAR TAU 120 AS IT SLOWS AND POTENTIALLY STALLS EAST OF NORTHERN
HONSHU. 

MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC GUIDANCE SUPPORTS
THIS SCENARIO WITH A DISTINCT SLOW DOWN AND WEAKENING TREND REFLECTED 
IN THE 050000Z GFS AND ECMWF ENSEMBLES. ADDITIONALLY, THERE ARE NO 
RECURVING SOLUTIONS, REINFORCING THE LACK OF A RECURVE MECHANISM. 
OVERALL, THERE IS MEDIUM CONFIDENCE IN THE JTWC FORECAST TRACK WITH 
MODEL GUIDANCE SHOWING SOME POTENTIAL FOR THE SYSTEM TO TRACK CLOSER 
TO THE KANTO PLAIN REGION.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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