WDPN31 PGTW 151500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W WARNING NR 04//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 12W (FANAPI), LOCATED APPROXIMATELY 
335 NM SOUTH OF OKINAWA, JAPAN HAS TRACKED NORTHWESTWARD AT 03 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY AND A 
151009Z SSMIS 91 GHZ MICROWAVE IMAGE DEPICT TIGHTLY CURVED 
CONVECTIVE BANDING WRAPPING IN FROM ALL QUADRANTS WITH DEEP 
CONVECTION BUILDING OVER THE SYSTEM CENTER. OVER THE PAST SIX HOURS 
THE SYSTEM HAS SLOWED CONSIDERABLY DUE TO A WEAKENING STEERING 
ENVIRONMENT. THE CURRENT POSITION IS BASED ON THE AFOREMENTIONED 
MICROWAVE PASS WITH FAIR CONFIDENCE. THE CURRENT INTENSITY IS BASED 
ON DVORAK ESTIMATES FROM PGTW, KNES, AND PGTW OF 35 KNOTS. UPPER 
LEVEL ANALYSIS REVEALS TS 12W IS EXPERIENCING IMPROVED EQUATORWARD 
OUTFLOW ASSOCIATED WITH THE TROPICAL UPPER TROPOSPHERIC TROUGH 
(TUTT) CELL APPROACHING FROM THE EAST AND A TUTT CELL MOVING AWAY 
FROM THE SYSTEM TO THE WEST. ANIMATED WATER VAPOR IMAGERY INDICATES 
AN APPROACHING MID-LATITUDE UPPER LEVEL TROUGH MAY BE STARTING TO 
ENHANCE POLEWARD OUTFLOW. OVERALL THE SYSTEM IS IN A FAVORABLE 
ENVIRONMENT FOR DEVELOPMENT WITH AN ANTICYCLONE OVER THE SYSTEM 
CENTER, LOW VERTICAL WIND SHEAR, AND HIGH SEA SURFACE TEMPERATURES.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE FROM THE PREVIOUS PROGNOSTIC
REASONING MESSAGE.
   B. TS 12W IS CURRENTLY TRACKING ALONG THE SOUTHWESTERN PERIPHERY 
OF A LOW TO MID-LEVEL STEERING RIDGE ANCHORED SOUTH OF JAPAN. NEAR 
TAU 12, A MID-LATITUDE TROUGH IS FORECAST TO WEAKEN THE STEERING 
RIDGE CAUSING THE SYSTEM TO SLOW AND TRACK POLEWARD. WITHIN THIS 
WEAKENED STEERING ENVIRONMENT, TS 12W IS EXPECTED TO INTENSIFY AS 
POLEWARD OUTFLOW IS ENHANCED BY THE MID-LATITUDE WESTERLY FLOW 
DIGGING DOWN TOWARD THE SYSTEM, AND EQUATORWARD OUTFLOW CONTINUES TO 
IMPROVE DUE TO THE TUTT CELL TO THE EAST. AFTER TAU 48 THE SYSTEM IS 
EXPECTED TO TURN BACK TOWARD THE NORTHWEST AS THE SUBTROPICAL RIDGE 
BUILDS BACK IN NORTH OF THE SYSTEM. 
   C. BY TAU 72, TS 12W IS FORECAST TO CONTINUE TRACKING 
NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF THE REBUILDING 
SUBTROPICAL RIDGE EXTENDING INTO EASTERN CHINA. THE SYSTEM IS 
FORECAST TO CONTINUE INTENSIFYING THROUGHOUT THE FORECAST PERIOD DUE 
TO FAVORABLE ENVIRONMENTAL CONDITIONS. NUMERICAL MODEL GUIDANCE 
REMAINS IN GOOD AGREEMENT WITH THE OVERALL TRACK PHILOSOPHY, BUT 
CONTINUES TO DEPICT UNCERTAINTY WITH THE TIMING OF THE TURN BACK TO 
THE NORTHWEST. GFDN AND GFS DEPICT A SLOWER TURN, WHILE ECMWF AND 
NOGAPS DEPICT A MORE RAPID TURN. THIS FORECAST FAVORS A QUICKER TURN 
BACK TO THE NORTHWEST AND IS CLOSE TO MODEL CONSENSUS.//
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