WDPN31 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SONGDA) 
WARNING NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.8N 125.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 121 NM SOUTHWEST OF JEJU ISLAND, S. KOREA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT,
CONSOLIDATING SYSTEM WITH FORMATIVE CONVECTIVE BANDING FROM THE
NORTH AND SOUTH WRAPPING INTO A WELL-DEFINED LOW-LEVEL CIRCULATION.
THE INITIAL POSITION AND INTENSITY ARE PLACED WITH HIGH CONFIDENCE
BASED ON EXTRAPOLATION FROM A 300207Z DIRECT ASCAT PASS SHOWING THE
STRONGEST WINDS ON A PATCH 60NM TO THE NORTH. THE INITIAL INTENSITY
OF 30KTS IS ALSO SUPPORTED BY THE RJTD DVORAK ESTIMATED OF T2.0 AND
CONSISTENT WITH THE SUSTAINED 6-HR CONVECTIVE SIGNATURE.
ENVIRONMENTAL CONDITIONS ARE FAVORABLE WITH MODERATE POLEWARD
OUTFLOW, LOW VERTICAL WIND SHEAR AND WARM SST.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A LOW- TO
MID-LEVEL SUBTROPICAL RIDGE (STR) TO THE NORTHEAST CENTERED OVER
CENTRAL JAPAN.


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 300158Z
   CIMSS ADT: 35 KTS AT 300250Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TD 06W WILL TRACK NORTHWESTWARD THROUGH TAU 12
THEN TURN SHARPLY NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR
WHICH IS EXPECTED TO ERODE WITH THE APPROACH OF A MIDLATITUDE
SHORTWAVE TROUGH. AFTER TAU 24, THE CYCLONE WILL ACCELERATE
NORTH-NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR, MAKING
LANDFALL OVER NORTH KOREA BEFORE TAU 66. FAVORABLE CONDITIONS WILL
FUEL INTENSIFICATION TO A PEAK OF 45KTS BY TAU 12. AFTERWARD,
INCREASING VWS AND COOLING SST WILL LEAD TO STEADY WEAKENING DOWN
TO 30KTS PRIOR TO LANDFALL, AND DISSIPATION BY TAU 72, AS LAND
INTERACTION SPEEDS UP THE EROSION.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH A GRADUAL AND EVEN SPREAD IN SOLUTIONS TO 160NM AT TAU 72,
LENDING MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST. 

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