WDPN31 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SONGDA) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.0N 131.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 260 NM NORTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS BROAD
EAST-WEST ELONGATED DEEP FLARING CONVECTION PARTIALLY OBSCURING A
LOW LEVEL CIRCULATION CENTER (LLCC) MOVING ALONG THE NORTHERN
PERIPHERY OF A MONSOON GYRE. A 290413Z AMSR2 89GHZ MICROWAVE IMAGE
INDICATES A BULK OF THE CONVECTIVE STRUCTURES LIE ALONG THE AXIS OF
STORM MOTION WITH WEAK RETURN FLOW INDICATED TO THE SOUTH OF THE
LLCC. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON THE ELONGATED NATURE OF THE SYSTEM SEEN IN BOTH THE MSI AND
AMSR2 IMAGING.  THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE AGREEMENT BETWEEN PGTW DVORAK
INTENSITY ESTIMATES AND CIMSS ADT WHICH BOTH REFLECT 30 KNOTS,
WHILE RJTD REMAINS SLIGHTLY HIGHER AT 35KTS.

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

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 32 KTS AT 290550Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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 (SONGDA) HAS TRACKED WEST-NORTHWESTWARD
UNDER THE STEERING INFLUENCE OF THE STR TO ITS NORTH. THROUGH TAU
36 THE SYSTEM IS FORECAST TO CONTINUE ITS WEST-NORTHWESTWARD
TRAJECTORY IN AN OVERALL 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 STR WHICH WAS PREVIOUSLY FORECAST TO STEER THE
SYSTEM JUST NORTH OF SHANGHAI, IS NOW SHOWING SIGNS OF
DETERIORATION AS A SHORT WAVE TROUGH MOVES IN FROM THE NORTHWEST.
THIS DEGRADATION OF THE STEERING RIDGE IN THE LATER TAUS COULD
ALLOW THE SYSTEM TO FOLLOW A MORE NORTHWESTWARD TRACK INTO THE
SOUTHWESTERN REGION OF THE YELLOW SEA AND EVENTUALLY DISSIPATE
CLOSER TO QINGDAO NEAR TAU 96.  

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT THAT THE
STEERING RIDGE TO THE NORTH OF THE SYSTEM WILL BREAK DOWN ALLOWING
THE SYSTEM TO TRACK FURTHER NORTH, THE MAGNITUDE AND TIMING OF THIS
NEW TREND IS NOT CLEAR AT THIS TIME. FOR THIS REASON THE JTWC TRACK
FORECAST IS PLACED WITH MEDIUM CONFIDENCE. RELIABLE MODEL INTENSITY
GUIDANCE IS IN GOOD AGREEMENT THAT AN INITIAL INTENSIFICATION TREND
IS POSSIBLE THROUGH TAU 12 TO TAU 24, WITH ONLY DECAY-SHIPS (GFS
VERSION) SHOWING AN UNREALISTIC CLIMB TO NEARLY 50 KNOTS. AFTER TAU
24 THE BULK OF THE GUIDANCE THEN BEGINS TO STAGNATE NEAR 35 KNOTS
AND EVENTUALLY DECAYS THE SYSTEM UNTIL DISSIPATION NEAR TAU 96.
FOR THIS REASON THE JTWC INTENSITY FORECAST IS PLACED WITH HIGH
CONFIDENCE.

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