WDPN31 PGTW 120300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SANBA) WARNING NR 
06//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 17W (SANBA), LOCATED APPROXIMATELY 640 NM
EAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 08 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
(MSI) SHOWS DEEP CONVECTIVE BANDING WRAPPING TIGHTLY INTO ALL 
QUADRANTS OF THE LOW LEVEL CIRCULATION CENTER. AN 112328Z SSMIS 
IMAGE INDICATES A MICROWAVE EYE HAS FORMED WITH THE DEEPEST 
CONVECTIVE BANDING ALONG THE NORTHERN AND SOUTHERN PERIPHERY. THE 
INITIAL INTENSITY IS BASED ON DVORAK ESTIMATES OF 55 KNOTS FROM KNES 
AND PGTW. POSITION IS BASED ON ANIMATED MSI AND THE AFOREMENTIONED 
MICROWAVE IMAGERY WITH HIGH CONFIDENCE. UPPER LEVEL ANALYSIS 
INDICATES THE SYSTEM IS LOCATED BENEATH AN UPPER LEVEL RIDGE AXIS IN 
A REGION OF LIGHT (05-10 KNOTS) VERTICAL WIND SHEAR. ANIMATED WATER 
VAPOR IMAGERY CONTINUES TO SHOW RADIAL OUTFLOW, ENHANCED BY A POINT 
SOURCE TO THE SOUTH OF THE SYSTEM AND A TROPICAL UPPER TROPOSPHERIC 
TROUGH (TUTT) TO THE NORTHEAST. OUTFLOW INTO THE TUTT HAS INCREASED 
DURING THE PAST SIX HOURS, RESULTING IN ENHANCED CONVECTIVE BANDING 
ON THE POLEWARD SIDE OF 17W. THE CYCLONE IS TRACKING ALONG THE 
WESTERN PERIPHERY OF A NEAR-EQUATORIAL RIDGE TO THE EAST.  
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. DUE TO THE INCREASED POLEWARD OUTFLOW AND SUBSEQUENT INCREASE 
IN INITIAL INTENSITY, FORECAST INTENSITIES HAVE INCREASED THROUGH 
TAU 72. TS 17W IS EXPECTED TO CONTINUE TRACKING NORTHWESTWARD AND 
STEADILY INTENSIFY AS UPPER LEVEL CONDITIONS AND WARM (28-30 DEGREES 
CELSIUS) SEA SURFACE TEMPERATURES PERSIST. AS THE STEERING REGIME OF 
17W TRANSITIONS FROM THE NEAR EQUATORIAL RIDGE TO THE SUBTROPICAL 
RIDGE (STR) TO THE EAST OF JAPAN, THIS SYSTEM IS EXPECTED TO BRIEFLY 
TRACK ON A MORE NORTHWARD TRAJECTORY NEAR TAU 36. 17W SHOULD RESUME 
A SLIGHTLY MORE NORTHWESTERLY TRACK AFTER TAU 36 AS THE SYSTEM MOVES 
AROUND THE WESTERN PERIPHERY OF THE STR. 
   C. AFTER TAU 72, SANBA IS EXPECTED TO REACH A PEAK INTENSITY OF 
115 KNOTS IN A VERY FAVORABLE ENVIRONMENT. 17W WILL BEGIN TO BE 
INFLUENCED BY AN APPROACHING MID-LATITUDE TROUGH AT THE 120 HOUR 
POINT AND BEGIN RECURVING SOUTH OF THE KOREAN PENINSULA.  AS THE 
SYSTEM SLOWLY RECURVES AND BEGINS TO INTERACT WITH THE WESTERLIES, 
INTENSITY IS EXPECTED TO GRADUALLY DECREASE. THE AVAILABLE NUMERICAL 
MODEL GUIDANCE IS IN GOOD AGREEMENT BEFORE TAU 72, WITH THE 
EXCEPTION OF NOGAPS, THE LEFT OUTLIER. AFTER TAU 72, GUIDANCE BEGINS 
TO SPREAD SLIGHTLY, WITH ECMWF CONTINUING TO FAVOR A MORE WESTERLY 
TRACK WEST OF OKINAWA AND INTO THE YELLOE SEA. NOGAPS AND GFS FAVOR 
A MORE EASTERLY TRACK TOWARD THE EASTERN SIDE OF THE KOREAN 
PENINSULA. THIS FORECAST IS CLOSE TO CONSENSUS AND IS JUST TO THE 
RIGHT OF THE PREVIOUS FORECAST TRACK. CONFIDENCE IN THIS FORECAST IS 
HIGH THROUGH TAU 72 AND LOW AFTERWARDS AS GUIDANCE REMAINS SPREAD UP 
TO 250 NM.//
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