WDPN31 PGTW 312100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SONGDA) 
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 34.9N 123.0E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 186 NM WEST-SOUTHWEST OF KUNSAN AB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
FULLY-EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION (LLC) WITH
ISOLATED DEEP CONVECTION SHEARED WELL NORTHEAST OF THE LLC. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EIR
IMAGERY. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON RECENT ASCAT DATA. TD 06W IS LOCATED UNDER
STRONG SOUTHWESTERLY FLOW ALOFT ASSOCIATED WITH AN UPPER-LEVEL
TROUGH POSITIONED OVER THE GULF OF POHAI. THIS UNFAVORABLE
ENVIRONMENT IS DOMINATED BY CONVERGENCE ALOFT, MODERATE TO HIGH
VERTICAL WIND SHEAR AND SIGNIFICANT DRY AIR.

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

CURRENT STEERING MECHANISM: THE SYSTEM IS TRACKING POLEWARD ALONG
THE WESTERN PERIPHERY OF A LOW-LEVEL SUBTROPICAL RIDGE POSITIONED
TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   CIMSS SATCON: 37 KTS AT 311308Z
   CIMSS ADT: 25 KTS AT 311750Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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: TROPICAL DEPRESSION 06W IS FORECAST TO
ACCELERATE NORTH-NORTHEASTWARD THROUGH THE FORECAST PERIOD AS IT
ROUNDS THE NORTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE.
ENVIRONMENTAL CONDITIONS WILL REMAIN UNFAVORABLE THUS THE SYSTEM
WILL GRADUALLY WEAKEN AS IT APPROACHES THE COAST OF SOUTHWEST NORTH
KOREA WITH DISSIPATION ANTICIPATED OVER THE NEXT 24 TO 36 HOURS BUT
POSSIBLY SOONER.  

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
SUPPORTING THE JTWC FORECAST TRACK WITH MEDIUM CONFIDENCE. DUE TO
THE SHALLOW, WEAK NATURE OF THE SYSTEM, THE TRACK HAS BEEN SOMEWHAT
ERRATIC BUT GENERALLY POLEWARD AND COULD REMAIN ERRATIC AS IT
TRACKS POLEWARD. THE INTENSITY FORECAST IS STRAIGHT-FORWARD WITH
RELIABLE INTENSITY GUIDANCE INCLUDING HWRF AND COAMPS-TC INDICATING
A STEADY WEAKENING TREND THROUGH THE FORECAST PERIOD. OVERALL,
THERE IS HIGH CONFIDENCE IN THE JTWC INTENSITY FORECAST.   

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