WDPN31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W 
(SONGDA) WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.7N 129.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 204 NM SOUTH OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS BROAD
EAST-WEST ELONGATED FLARING CONVECTION MOVING ALONG THE NORTHERN
PERIPHERY OF A MONSOON GYRE. A 291202Z ASCAT-B PASS SHOWS A VERY
FRAGILE CIRCULATION WITH WEAK RETURN FLOW ON THE SOUTHERN
SEMICIRCLE BUT LARGE SWATHS OF 25-30 KNOT WINDS IN THE NORTHERN
SEMICIRCLE. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EIR AND FORTUITOUS ASCAT IMAGE. THE INITIAL INTENSITY
OF 30 KTS IS ALSO ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT
IMAGE.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T1.0 - 25 KTS
   CIMSS ADT: 34 KTS AT 291150Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: AN EXTENSION TO THE STR PREVIOUSLY
FORECAST TO CARRY THE SYSTEM GENERALLY WEST-NORTHWESTWARD IS NOW 
FORECAST TO BREAKDOWN CONSIDERABLY ALLOWING FOR A MORE NORTHWARD 
RECURVE AFTER TAU 36, GENERALLY TOWARD THE KOREAN PENINSULA.

FORECAST DISCUSSION: TD 06W (SONGDA) HAS TRACKED WEST-NORTHWESTWARD
UNDER THE STEERING INFLUENCE OF THE STR TO ITS NORTHEAST. THROUGH
TAU 36 THE SYSTEM IS FORECAST TO CONTINUE ITS WEST-NORTHWESTWARD
TRAJECTORY IN AN OVERALL MARGINALLY FAVORABLE ENVIRONMENT. THE MAIN
HINDRANCE TO INTENSIFICATION IS THE LACK OF A COHESIVE LOW LEVEL
CIRCULATION DUE TO THE FACT THAT THIS SYSTEM LIES ALONG THE
NORTHERN PERIPHERY OF THE MONSOON GYRE WHICH IS SLOWING THE
CONSOLIDATION OF THE LOW LEVEL CORE. THE EXTENSION OF THE STR WHICH
WAS PREVIOUSLY FORECAST TO CARRY THE SYSTEM GENERALLY WEST-
NORTHWESTWARD IS NOW FORECAST TO BREAKDOWN CONSIDERABLY ALLOWING FOR 
A MORE NORTHWARD RECURVE AFTER TAU 36, GENERALLY TOWARD THE KOREAN 
PENINSULA. THIS MORE NORTHWARD TRAJECTORY AFTER TAU 36 MAY ALSO ALLOW 
TD 06W TO MAINTAIN AND EVEN BRIEFLY INCREASE IN INTENSITY THROUGH TAU 
72. AFTER TAU 72 HOWEVER, AS THE SYSTEM APPROACHES LAND, DRY AIR 
ENTRAINMENT AND COOLER SEA SURFACE TEMPERATURES (SST), WILL BEGIN TO 
SIGNIFICANTLY IMPACT THE SYSTEMS INTENSITY UNTIL EVENTUAL DISSIPATION 
NEAR TAU 96.

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM AND COTI (NVGM
VERSION), NUMERICAL MODELS ARE IN GOOD AGREEMENT THAT THE STEERING
RIDGE TO THE NORTHEAST OF THE SYSTEM WILL BREAK DOWN ALLOWING THE
SYSTEM TO TRACK GENERALLY NORTHWARD AFTER TAU 36 UNTIL DISSIPATION
AROUND TAU 96. FOR THIS REASON THE JTWC TRACK FORECAST IS PLACED
WITH MEDIUM CONFIDENCE AND EVENTUALLY LOW CONFIDENCE AFTER TAU 72
DUE TO CROSS ALONG TRACK DISAGREEMENT. WITH THE EXCEPTION OF COTI
(NVGM VERSION), RELIABLE MODEL INTENSITY GUIDANCE IS IN FAIR
AGREEMENT THAT THE SYSTEM MAY INTENSIFY THROUGH TAU 48 WITH THE
BULK OF THE GUIDANCE REMAINING BETWEEN 35-40 KNOTS, AFTER WHICH A
UNANIMOUS WEAKENING TREND THROUGH THE FORECAST PERIOD. FOR THIS
REASON THE JTWC INTENSITY FORECAST IS PLACED WITH HIGH CONFIDENCE.



FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: HIGH//
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