WDPN31 PGTW 311500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SONGDA) 
WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 34.3N 123.2E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 193 NM WEST-SOUTHWEST OF KUNSAN AB, S.
KOREA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN
EXPOSED LOW LEVEL CIRCULATION (LLC) WITH RAPIDLY ERODING DEEP
CONVECTION THAT IS DECOUPLED FROM THE LLC AND STRETCHED POLEWARD.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE 
EXPOSED LLC FEATURE. THE INITIAL INTENSITY IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON THE PGTW DVORAK ESTIMATE, EXTRAPOLATION FROM 
NEARBY SURFACE WIND OBSERVATIONS, INCLUDING ONE FROM A BUOY 15NM TO 
THE SOUTHWEST, AND REFLECTS THE 6-HR DEGRADED CONVECTIVE STRUCTURE.
AUTOMATED DVORAK VALUES APPEAR TO BE OVER-ESTIMATED. TD 06W IS IN
AN UNFAVORABLE ENVIRONMENT WITH STRONG POLEWARD OUTFLOW OFFSET BY
MODERATE (15-20KTS) VWS AND COOLING (27-26C) SSTS IN THE YELLOW
SEA.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A STRONG
SUBTROPICAL RIDGE (STR) CENTERED SOUTH OF CENTRAL JAPAN.


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 37 KTS AT 310850Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TD SONGDA WILL TRACK NORTHEASTWARD ALONG THE
NORTHWESTERN PERIPHERY OF THE STR. THE UNFAVORABLE ENVIRONMENT WILL
CONTINUE TO ERODE THE SYSTEM AND CAUSE ITS DISSIPATION BY TAU 24,
POSSIBLY SOONER, IN THE YELLOW SEA. THE REMNANT LOW WILL TRACK
TOWARD NORTH KOREA.

MODEL DISCUSSION: NUMERICAL MODELS ARE GENERALLY IN AGREEMENT WITH
SOME MEMBERS BECOMING MORE ERRATIC, AN INDICATION OF A WEAK VORTEX.
IN VIEW OF THIS, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC TRACK
AND INTENSITY FORECASTS.

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