WDPN31 PGTW 180300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W WARNING NR 27//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM 18W (ROKE), LOCATED APPROXIMATELY 180 NM EAST-
SOUTHEAST OF KADENA AB, JAPAN, HAS TRACKED NORTHEASTWARD AT 04 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS TIGHTLY CURVED BANDING WRAPPING INTO THE LOW 
LEVEL CIRCULATION CENTER (LLCC). A 172035Z TRMM MICROWAVE IMAGE 
DEPICTS A SMALL DEEP CONVECTIVE EYE WITH A LARGE CONVECTIVE BAND ON 
THE SOUTHERN PERIPHERY. HOWEVER, A MORE RECENT 172333Z SSMIS IMAGE 
INDICATES THERE IS NO LONGER A MICROWAVE EYE AND ONLY CURVED 
CONVECTION ALONG THE SOUTHERN PERIPHERY. THE INITIAL POSITION IS 
BASED ON THE AFOREMENTIONED MICROWAVE IMAGERY AND MSI WITH FAIR 
CONFIDENCE. THE INITIAL INTENSITY IS BASED ON A RCTP DOTSTAR FIX 
REPORTING 60 KNOTS CLOSE TO THE CENTER OF THE LLCC. WATER VAPOR 
IMAGERY INDICATES A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) IS 
WRAPPING AROUND FROM THE NORTHEAST AND CAUSING SUBSIDENCE ALONG THE 
NORTHERN PERIPHERY. THE POLEWARD OUTFLOW CHANNEL HAS WEAKENED, 
ALTHOUGH EQUATORWARD OUTFLOW REMAINS FAVORABLE. TS 18W HAS LOOPED 
NORTHEASTWARD WITHIN A WEAK STEERING ENVIRONMENT BETWEEN A 
SUBTROPICAL RIDGE TO THE NORTHEAST AND NORTHWEST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. TS 18W IS EXPECTED TO CONTINUE TURNING POLEWARD IN THE WEAK 
STEERING ENVIRONMENT OVER THE NEXT 24 HOURS. THE SYSTEM IS THEN 
FORECAST TO TURN NORTHEASTWARD AS A MID-LATITUDE TROUGH WEAKENS THE 
STEERING RIDGE TO THE NORTHEAST. TS 18W SHOULD CONTINUE TO INTENSIFY 
SLIGHTLY DUE TO HIGH SEA SURFACE TEMPERATURES AND GOOD EQUATORWARD 
OUTFLOW. HOWEVER, THE TUTT INTERACTION SHOULD LIMIT INTENSIFICATION.
   C. AT TAU 72, TS 18W WILL BEGIN TO INTERACT WITH THE BAROCLINIC 
ZONE AND TRANSITION INTO A STRONG EXTRA-TROPICAL LOW BY TAU 120. THE 
AVAILABLE NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH THE INITIAL 
TURN NORTHWARD. HOWEVER, UKMO, JGSM, AND GFS TRACK THE SYSTEM 
FARTHER WESTWARD BACK TOWARDS OKINAWA. THE MODELS ARE ALSO IN 
AGREEMENT WITH THE TURN TO THE NORTHEAST ALTHOUGH THEY VARY IN THE 
TIMING OF THE TURN.//
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