WDPN31 PGTW 310300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE) WARNING 
NR 01//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 09W (NINE), LOCATED APPROXIMATELY 451 NM
SOUTH-SOUTHEASTWARD OF HONG KONG, HAS TRACKED WEST-NORTHWESTWARD
AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY (MSI) DEPICTS IMPROVED DEEP CONVECTION LOOSELY 
WRAPPING A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) WITH A 
LARGE, ALBEIT BROKEN, BANDING FEATURE ALONG THE SOUTHERN PERIPHERY 
THAT SPANS ACROSS THE SOUTHERN SOUTH CHINA SEA. A 302151Z SSMIS 
91GHZ MICROWAVE IMAGER REVEALS DISORGANIZED DEEP CONVECTION AROUND 
AN OVERALL BROAD AND POORLY DEFINED LLCC. SHIP OBSERVATIONS IN THE 
AREA CONTINUE TO SHOW FALLING SEA-LEVEL PRESSURE VALUES AND WINDS 
THAT RANGE FROM 15-20 KNOTS. THERE IS LOW CONFIDENCE IN THE INITIAL 
POSITION AS THE LLCC REMAINS FAIRLY AMBIGUOUS IN THE MSI AND 
MICROWAVE IMAGERY. THE INITIAL INTENSITY HAS BEEN ASSESSED AT 30 
KNOTS BASED UPON DVORAK INTENSITY ESTIMATES FROM RJTD AND KNES. 
UPPER-LEVEL ANALYSIS REVEALS A FAVORABLE ENVIRONMENT AS THE SYSTEM 
IS UNDER LOW VERTICAL WIND SHEAR (05-10 KNOTS) AND FAVORABLE OUTFLOW 
THAT IS BEING ENHANCED BY A TUTT CELL LOCATED EAST OF TAIWAN. TD 09W 
IS SLOWLY MOVING WEST-NORTHWESTWARD AS IT CONSOLIDATES AND TRACKS 
ALONG AN EXTENSION OF THE MID TO DEEP-LAYERED SUBTROPICAL STEERING 
RIDGE.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING AND SETS THE FORECAST 
PHILOSOPHY.
   B. TD 09W IS EXPECTED TO CONTINUE TO SLOWLY TRACK WEST-NORTHWEST 
ALONG THIS EXTENSION OF THE STR THROUGH TAU 36. AFTER TAU 36, THE 
STEERING STR IS EXPECTED TO AMPLIFY IN RESPONSE TO A MID-LATITUDE 
TROUGH THAT IS CURRENTLY LOCATED OVER CENTRAL CHINA. THIS 
AMPLIFICATION OF THE RIDGE WILL CAUSE TD 09W TO ACCELERATE MORE 
WESTWARD TOWARDS HAINAN ISLAND, MAKING LANDFALL AFTER TAU 48. 
GENERAL INTENSIFICATION IS EXPECTED THROUGH TAU 48 AS FAVORABLE 
ENVIRONMENTAL CONDITIONS OF ROBUST OUTFLOW, LOW VWS, AND FAVORABLE 
SEA-SURFACE TEMPERATURES REMAIN CONSTANT. THIS SHOULD ALLOW TD 09W 
TO REACH A MAX INTENSITY OF 50 KNOTS AT TAU 48. AFTER TAU 48, 
INCREASING VWS AND LAND INTERACTION WITH HAINAN ISLAND WITH BEGIN TO 
WEAKEN THE SYSTEM.
   C. IN THE EXTENDED TAUS, TD 09W WILL MAKE LANDFALL AGAIN INTO 
NORTHERN VIETNAM. THE FRICTIONAL EFFECTS OF THIS ROUGH TERRAIN WILL 
ERODE THE SYSTEM LEADING TO ITS DISSIPATION BY TAU 96 AS IT 
CONTINUES TO TRACK WEST. DYNAMIC MODEL GUIDANCE IS GENERALLY IN GOOD 
AGREEMENT WITH THE FORECAST TRACK ALTHOUGH THERE IS SOME 
DISAGREEMENT ON THE TRACK SPEED OF THE SYSTEM. DUE TO THIS SLIGHT 
DISAGREEMENT OF THE TRANSLATIONAL SPEED AND THE LOW CONFIDENCE IN 
THE INITIAL POSITION, THERE IS LOW CONFIDENCE IN THE FORECAST WHICH 
IS CLOSE TO MULTI-MODEL CONSENSUS.//
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