WDPN31 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SANVU) WARNING NR 
07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 17W (SANVU), LOCATED APPROXIMATELY 129 NM EAST OF
CHICHI JIMA, JAPAN, HAS TRACKED NORTHWESTWARD AT 17 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS
THE LARGE CONVECTIVE BANDING HAS WRAPPED TIGHTER INTO A BROAD,
WELL-DEFINED, ALBEIT PARTLY EXPOSED LOW LEVEL CIRCULATION (LLC). THE
FEEDER BAND REMAINS EXTENSIVE AND TRAILS THE LLC BY OVER 900NM. THE
INITIAL POSITION IS BASED WITH FAIR CONFIDENCE ON THE MSI LOOP. THE
INITIAL INTENSITY OF 55 KNOTS IS BASED ON CONGRUENT DVORAK ESTIMATES
OF T3.5 FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM
IS IN AN AREA OF LOW TO MODERATE (10-15 KNOT) VERTICAL WIND SHEAR
(VWS) AND EXCELLENT DUAL OUTFLOW. ADDITIONALLY, SEA SURFACE
TEMPERATURES (SST) AT 30 CELSIUS ARE CONDUCIVE FOR FURTHER
DEVELOPMENT. TS 17W IS TRACKING ALONG THE SOUTHWESTERN EDGE OF THE
DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTHEAST. 
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 17W IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD ALONG THE
SOUTHWESTERN EXTENT OF THE STR AS THE STR BUILDS. AFTER TAU 12, IT
WILL BEGIN TO SLOW AND TRACK NORTH THEN NORTHEASTWARD AS IT ROUNDS THE
WESTERN EDGE OF THE STR. THE CYCLONE WILL REMAIN IN A FAVORABLE
ENVIRONMENT WITH INCREASED POLEWARD OUTFLOW INTENSIFYING THE SYSTEM
TO A PEAK OF 80 KNOTS BY TAU 72. MODEL GUIDANCE REMAINS IN FAIRLY
TIGHT AGREEMENT WITH JENS AND JGSM ON THE LEFT MARGIN OF THE MODEL
ENVELOPE. THE JTWC TRACK FORECAST IS LAID JUST TO THE RIGHT OF CONW
TO OFFSET THESE OUTLIERS. 
   C. AFTER TAU 72, TS SANVU WILL SIGNIFICANTLY ACCELERATE
NORTHEASTWARD AS IT GETS EMBEDDED IN THE PREVAILING WESTERLIES.
CONCURRENTLY, IT WILL BEGIN EXTRA TROPICAL TRANSITION (ETT) AND WILL
GRADUALLY ERODE MAINLY DUE TO INCREASING VWS. BY TAU 96, TS 17W WILL
COMPLETE ETT AND BECOME A STRONG GALE-FORCE COLD CORE LOW. MODEL
GUIDANCE CONTINUES TO BE IN GOOD AGREEMENT. THIS PORTION OF THE JTWC
TRACK FORECAST IS LAID WITH HIGH CONFIDENCE SLIGHTLY TO THE RIGHT AND
FASTER THAN CONW.//
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