WDPN35 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (JONGDARI) WARNING 
NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 15W (JONGDARI), LOCATED APPROXIMATELY 215 NM 
SOUTHWEST OF IWO TO, HAS TRACKED EAST-NORTHEASTWARD AT 08 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
DEPICTS A SMALL, CONSOLIDATED SYSTEM WITH DEEP CONVECTION OBSCURING 
THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS 
PLACED WITH GOOD CONFIDENCE BASED ON A 260036Z AMSU 89 GHZ IMAGE 
SHOWING DEEP BANDING WRAPPING AROUND FROM THE NORTH AND SOUTH. THE 
INITIAL  INTENSITY OF 55 KNOTS IS BASED ON DVORAK CURRENT INTENSITY 
ESTIMATES OF T3.5 (55 KNOTS) FROM PGTW AND RJTD. UPPER-LEVEL 
ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH GOOD POLEWARD AND 
EQUATORWARD OUTFLOW AND LOW VERTICAL WIND SHEAR. TS 15W IS TRACKING 
ALONG THE NORTHERN PERIPHERY OF THE NEAR-EQUATORIAL RIDGE (NER) 
POSITIONED TO THE SOUTH.    
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 15W IS FORECAST TO CONTINUE TRACKING ALONG THE NORTHERN 
PERIPHERY OF THE NER THROUGH TAU 24. BETWEEN TAU 36 AND 48, TS 15W 
WILL GRADUALLY TURN NORTHWESTWARD AS A SUBTROPICAL RIDGE (STR) TO 
THE NORTHEAST BEGINS TO DOMINATE THE STEERING. THE SYSTEM IS 
FORECAST TO INTENSIFY THROUGH TAU 48 TO A PEAK OF 100 KNOTS AS 
POLEWARD OUTFLOW IS ENHANCED BY AN UPPER LEVEL LOW TO THE WEST. THE 
PEAK INTENSITY FORECAST IS ABOVE THE CONSENSUS AND CLOSELY FOLLOWS 
HWRF. AFTER TAU 48, THE OUTFLOW WILL BE REDUCED AND A GRADUAL 
WEAKENING TREND WILL BEGIN UNTIL MAKING LANDFALL PRIOR TO TAU 72 AT 
WHICH POINT TS 15W WILL BEGIN LAND INTERACTION, WHICH WILL WEAKEN 
THE CYCLONE CONSIDERABLY. NUMERICAL MODEL GUIDANCE IS IN FAIR 
AGREEMENT THROUGH TAU 36. AFTER TAU 36, THE UNCERTAINTY BEGINS TO 
INCREASE AS THE MEMBERS DIFFER ON WHEN THE STR TAKES OVER THE 
PRIMARY STEERING. BY TAU 72, THE SPREAD IS QUITE LARGE WITH SEVERAL 
MEMBERS BRINGING THE TRACK FURTHER SOUTH, TOWARD IWAKUNI, WHILE 
THERE IS ONE MEMBER (HWRF) THAT BRINGS THE CYCLONE NORTH OF TOKYO. 
CONFIDENCE IS LOW IN THIS PORTION OF THE JTWC FORECAST TRACK.
   C. AFTER TAU 72, UNCERTAINTY IN THE NUMERICAL MODEL GUIDANCE 
CONTINUES TO BE LARGE AS TS 15W BEGINS TO BE STEERED WESTWARD BY 
ANOTHER STR TO THE NORTHWEST. THE JTWC FORECAST TRACK IS HEDGED 
SLIGHTLY NORTH OF THE MULTI-MODEL CONSENSUS, CLOSE TO THE ECMWF 
FORECAST TRACK. JUST PRIOR TO TAU 72, TS 15W IS FORECAST TO PASS 
OVER HONSHU INTO THE SEA OF JAPAN AND WEAKEN SIGNIFICANTLY DUE TO 
INTERACTION WITH THE UPPER LOW AND THE FRICTIONAL EFFECTS OF LAND. 
OVERALL, FORECAST CONFIDENCE IS LOW, PARTICULARLY IN THE LATER 
PORTIONS OF THIS FORECAST.//
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