WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SONGDA) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.8N 128.0E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 163 NM SOUTH-SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS FLARING,
WEAKLY-ORGANIZED DEEP CONVECTION OVER A MID-LEVEL CIRCULATION WITH
A LINE OF DEEP CONVECTION EXTENDING TO THE SOUTHWEST. A 291806Z
ATMS 88.2GHZ MICROWAVE IMAGE ALSO DEPICTS A WEAKLY ORGANIZED
SYSTEM. ANIMATED RADAR IMAGERY INDICATES WEAK CYCLONIC TURNING,
WHICH CORRESPONDS TO THE JMA RADAR FIXES, WITH CURVED RAINBANDS
OVER THE NORTH AND EAST QUADRANTS BUT SCANT EVIDENCE OF A DISTINCT
CLOSED CIRCULATION AT THE SURFACE. RECENT ASCAT IMAGERY SHOWED A
WAVE FEATURE WITH NO CLOSED CIRCULATION, AND SURFACE OBSERVATIONS 
SOUTH OF KYUSHU ISLAND SHOWED 16-22 KNOT EASTERLY TO SOUTHEASTERLY 
WINDS WITH NO WESTERLY WINDS REPORTED. ADDITIONALLY, A RELATIVELY 
UNIMPRESSIVE MINIMUM SEA LEVEL PRESSURE VALUE OF 1003.6MB WAS 
REPORTED AT YAKUSHIMA AT 291100Z AS THE SYSTEM TRACKED OVER EARLIER. 
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON RADAR 
IMAGERY AND SATELLITE FIXES. THE INITIAL INTENSITY OF 25 KTS IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW, KNES DVORAK 
ESTIMATES AND SURFACE OBSERVATION DATA. ENVIRONMENTAL CONDITIONS ARE 
FAVORABLE WITH MODERATE POLEWARD OUTFLOW, LOW VERTICAL WIND SHEAR AND 
WARM SST VALUES (29C).

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE CENTERED OVER CENTRAL JAPAN.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   CIMSS ADT: 34 KTS AT 291750Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: ALTHOUGH THE SYSTEM IS WEAKLY-ORGANIZED AT THE
SURFACE, IT IS FORECAST TO INTENSIFY SLIGHTLY AND BECOME BETTER
ORGANIZED AS IT TRACKS WEST-NORTHWESTWARD OVER THE NEXT 24 HOURS
WITH A PEAK OF 35 KNOTS NEAR TAU 24. AFTER TAU 24, THE SUBTROPICAL
RIDGE (STR) IS EXPECTED TO ERODE WITH THE APPROACH OF A MIDLATITUDE
SHORTWAVE TROUGH, WHICH WILL TURN THE SYSTEM SHARPLY POLEWARD. AS
THE SYSTEM STEADILY TRACKS POLEWARD, IT IS EXPECTED TO WEAKEN DUE
TO INCREASING VERTICAL WIND SHEAR, COOLING SST (25C), INCREASING
DRY AIR ENTRAINMENT AND EVENTUALLY INTERACTION WITH LAND.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH A 145NM SPREAD IN SOLUTIONS AT TAU 72. NAVGEM IS THE EASTERN
OUTLIER AND INDICATES A SHARP NORTHWARD TURN AT TAU 24 WHILE GFS
TRACKS THE SYSTEM NORTH-NORTHWESTERLY INTO THE SHORTWAVE TROUGH.
THE JTWC FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL
CONSENSUS WITH THE BULK OF THE GUIDANCE WITH MEDIUM OVERALL
CONFIDENCE. 

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