WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (THIRTEEN) WARNING 
NR 14//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 13W (THIRTEEN), LOCATED APPROXIMATELY 840 NM NORTH-
NORTHWEST OF WAKE ISLAND, HAS TRACKED NORTHWESTWARD AT 14 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) 
DEPICTS INCREASING CENTRAL CONVECTION THAT IS BEGINNING TO WRAP 
AROUND THE LOW LEVEL CIRCULATION CENTER (LLCC). A 072202Z SSMIS 
37GHZ IMAGE AND A 072305Z AMSU 89GHZ IMAGE BOTH DEPICT A TIGHTLY 
WOUND SYSTEM WITH FRAGMENTED DEEP CONVECTIVE BANDING WRAPPING INTO 
THE LLCC. TS 13W IS MAINTAINING AS A TROPICAL, WARM-CORE SYSTEM AS 
THE MOST RECENT (071800Z) AMSU CROSS-SECTION INDICATES A 
STRENGTHENING +2C WARM-CORE TEMPERATURE ANOMALY AND A RECENT 072305 
ASCAT PASS STILL SHOWS A SYMMETRIC WIND FIELD. INITIAL POSITION IS 
BASED ON THE AFOREMENTIONED IMAGERY AND A PGTW FIX. INTENSITY IS 
HEDGED HIGHER THAN THE PGTW DVORAK ESTIMATES OF 35 KNOTS DUE THE 
ASCAT PASS AND RECENT IMPROVEMENT IN STORM STRUCTURE. UPPER-LEVEL 
ANALYSIS INDICATES THAT TS 13W IS LOCATED SOUTH OF THE SUBTROPICAL 
RIDGE, IS UNDER WEAK (05-10 KNOT) VERTICAL WIND SHEAR, AND THE UPPER 
LEVEL LOW THAT HAD BEEN SUPPRESSING THE CENTRAL CONVECTION HAS MOVED 
TO THE SOUTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 13W IS EXPECTED TO TRACK UNDER THE SOUTHWESTERN PERIPHERY 
OF THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST. THE SYSTEM IS 
FORECAST TO TRACK OVER INCREASINGLY COOLER SEA SURFACE TEMPERATURE 
(< 25C) AT 38 DEGREES NORTH (SHORTLY AFTER TAU 36) AND WILL BEGIN TO 
INTERACT WITH THE EASTERN PERIPHERY OF A SHORTWAVE TROUGH WHICH IS 
EXPECTED TO DEEPEN EAST OF JAPAN. THIS SHORTWAVE TROUGH IS 
ASSOCIATED WITH THE SUBTROPICAL JET AND HAS WEAK BAROCLINICITY, 
THEREFORE, THE SYSTEM IS NOT EXPECTED TO UNDERGO EXTRA-TROPICAL 
TRANSITION AND SUBTROPICAL TRANSITION IS THE MOST LIKELY RESULT. 
SLIGHT WEAKENING IS FORECAST BUT TS 13W IS EXPECTED TO MAINTAIN GALE 
FORCE INTENSITY THROUGH TAU 48 AND COMPLETE TRANSITION INTO A 
SUBTROPICAL LOW. ALTHOUGH THE FORECAST CONFIDENCE FOR THE TIMING OF 
TRANSITION TO SUBTROPICAL LOW IS LOW THE TRACK AND INTENSITY 
FORECAST CONFIDENCE IS HIGH AS MODELS ARE IN TIGHT AGREEMENT.//
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