WDPN31 PGTW 071500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 01W (SONAMU) 
WARNING NR 17//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 01W (SONAMU), LOCATED APPROXIMATELY 290 
NM SOUTH-SOUTHEAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED 
SOUTHWESTWARD AT 01 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED 
INFRARED IMAGERY (EIR) SHOWS A RAPIDLY DETERIORATING, PARTIALLY 
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION 
ALONG THE WESTERN PERIPHERY. THE SHALLOW LOW LEVEL STRUCTURE CAN BE 
SEEN IN A 070755Z AMSU 89 GHZ MICROWAVE IMAGE. THE INITIAL POSITION 
IS BASED ON THE EIR AND EXTRAPOLATED FROM THE AFOREMENTIONED 
MICROWAVE IMAGE WITH POOR CONFIDENCE. THE SYSTEM APPEARS TO BE 
NEARLY QUASI-STATIONARY. THE INITIAL INTENSITY IS ASSESSED AT 30 
KNOTS BASED ON DECLINING DVORAK ESTIMATES FROM RJTD AND PGTW, AND 
TAKING INTO ACCOUNT THE POOR STRUCTURAL ORGANIZATION. THE TOTAL 
PERCEPTIBLE WATER LOOP CONTINUES TO INDICATE A POCKET OF DRY AIR IS 
WRAPPING ALONG THE EASTERN HALF OF THE LLCC TOWARDS THE SYSTEM 
CENTER. UPPER LEVEL ANALYSIS INDICATES TD 01W IS NEARLY 7 DEGREES 
SOUTH OF A SUBTROPICAL RIDGE (STR) AXIS IN A MODERATE TO HIGH 
VERTICAL WIND SHEAR (VWS) ENVIRONMENT (20 TO 30 KNOTS). ANIMATED 
WATER VAPOR IMAGERY REVEALS AN APPROACHING MID-LATITUDE LONG-WAVE 
TROUGH IS BEGINNING TO IMPINGE ON THE POLEWARD OUTFLOW. THE LATEST 
SEA SURFACE TEMPERATURE (SST) INDICATES THE WATERS AROUND TD 01W 
HAVE BECOME MARKEDLY COOLER (BELOW 26 DEGREES CELSIUS) AS A RESULT 
OF THE SLOW STORM MOTION AND SHALLOW LAYER OF AVAILABLE HEAT.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 01W IS FORECAST TO REMAIN IN A WEAK STEERING ENVIRONMENT, 
PREDOMINANTLY CONTROLLED BY THE LOW LEVEL ENVIRONMENTAL WIND FLOW. 
BASED ON INTENSITY GUIDANCE THE SYSTEM IS EXPECTED TO DISSIPATE OVER 
WATER BY 36 HOURS, HOWEVER THE DISSIPATION MAY OCCUR SOONER AS A 
RESULT OF THE HIGH VWS, DRY AIR ENTRAINMENT AND UNFAVORABLE SST. 
TRACK-WISE, THE DYNAMICAL MODELS ARE NOW IN MUCH BETTER AGREEMENT 
FOR WHAT IS LEFT OF TD 01W. THE OFFICIAL FORECAST IS NOW IN VERY 
CLOSE AGREEMENT WITH THE CONSENSUS OF AVAILABLE MODEL GUIDANCE. DUE 
TO THE GOOD AGREEMENT AMONG THE FORECAST AIDS, THERE IS HIGH 
CONFIDENCE IN THE JTWC FORECAST.//
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