WDPN31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (CIMARON) 
WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.2N 132.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 569 NM SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION 18W (CIMARON) WITH A WELL-DEFINED, EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH CONVECTION PERIODICALLY FLARING OVER
THE EASTERN PERIPHERY. HIGH WESTERLY VERTICAL WIND SHEAR CAN BE
SEEN BLOWING THE CONVECTION OFF TO THE EAST. ENVIRONMENTAL ANALYSIS
INDICATES THAT 18W IS IN A MARGINALLY UNFAVORABLE ENVIRONMENT 
CHARACTERIZED BY WEAK OUTFLOW ALOFT, MODERATE TO HIGH (20-25 KTS) 
VERTICAL WIND SHEAR, AND DRY AIR PLACED OVER THE WESTERN PORTION OF 
THE CIRCULATION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EXPOSED LLCC IN ANIMATED MSI. THE INITIAL INTENSITY OF
30 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE HIGH END OF
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T1.0 - 25 KTS
   CIMSS ADT: 32 KTS AT 260000Z
   CIMSS AIDT: 37 KTS AT 260000Z
   CIMSS DPRINT: 25 KTS AT 260000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE
   VWS: 20-25 KTS
   SST: 29-29 CELSIUS
   OUTFLOW: WEAK EASTWARD
   OTHER FACTORS: DRY AIR OVER THE WESTERN PORTION OF THE LLCC.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE TRACK HAS BEEN SIGNIFICANTLY
SHORTENED TO 36 HOURS WITH DISSIPATION OVER WATER RATHER THAN
EXTRATROPICAL TRANSITION. THE FRONTAL BOUNDARY RUNNING PARALLEL TO
THE COAST OF JAPAN IS EXPECTED TO QUICKLY WEAKEN THE VORTEX AS IT
BEGINS TO INTERACT WITH IT. 

FORECAST DISCUSSION: 18W IS EXPECTED TO CONTINUE GENERALLY
NORTHWESTWARD OVER THE NEXT 12 HOURS. AFTER TAU 12, 18W IS FORECAST
TO TURN NORTHWARD AS IT BEGINS TO ROUND THE STR TO ITS EAST. THE
SYSTEM IS EXPECTED TO REMAIN AROUND 25-30 KTS AS IT BEGINS THIS
TURN. NEAR TAU 36, 18W IS FORECAST TO BEGIN INTERACTING WITH THE
FRONTAL BOUNDARY RUNNING PARALLEL TO JAPAN, AND THE VORTEX WILL
QUICKLY BEGIN TO ELONGATE AND ERODE AS A RESULT. THE JTWC FORECAST
CALLS FOR DISSIPATION OVER WATER SOUTHEAST OF KYUSHU AS THE SYSTEM
UNRAVELS INTO TROUGHING. WINDS ALONG THE FRONTAL BOUNDARY MAY
CONTINUE TO SPIN UP SMALLER VORTICES AFTER 18W HAS DISSIPATED.  

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT
REGARDING THE TRACK OF 18W. MODELS HAVE CONTINUED TO HINT MORE AND
MORE AT A DISSIPATION SCENARIO VICE EXTRATROPICAL TRANSITION. THE
VORTEX BECOMES LOST IN NEARLY ALL RELIABLE GUIDANCE AROUND TAU
36-48. THE ECMWF DETERMINISTIC AND ENSEMBLE BOTH SUGGEST QUICK
DISSIPATION (AROUND 24 HOURS) WITH A STRAIGHT WESTWARD TRACK. THE
GFS AND ITS ENSEMBLE BOTH SUGGEST A SHORT TRACK NORTHWARD ALONG THE
RIDGE WITH DISSIPATION AROUND TAU 36-48. HAFS-A ALSO HAS 18W
BRIEFLY TRACKING AROUND THE RIDGE BEFORE DISSIPATION SIMILAR TO
GFS. THE JTWC TRACK IS PLACED CLOSER TO THE GFS AND HAFS-A WITH LOW
CONFIDENCE. INTENSITY GUIDANCE IS IN BETTER AGREEMENT WITH A STEADY
WEAKENING TREND OVER THE NEXT 36 HOURS. THE JTWC INTENSITY FORECAST
IS PLACED WITH MEDIUM CONFIDENCE AS A RESULT.

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