WDPN31 PGTW 130300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (CHOI-WAN)/
WARNING NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. ANIMATED MULTISPECTRAL IMAGERY SHOWS MULTIPLE SPIRAL BANDS
WRAPPING INTO DEEP, CENTRAL CONVECTION. A 122104Z SSMIS MICROWAVE
IMAGE ALSO RELECTS A CENTRALIZED CONVECTIVE STRUCTURE WITH THE
DEEPEST CONVECTION WRAPPING INTO THE LOW LEVEL CIRCULATION CENTER
(LLCC) FROM THE SOUTHWEST AND EAST. THE MULTISPECTRAL IMAGERY IN
CONCERT WITH THE ANIMATED WATER VAPOR IMAGERY ALSO DEPICT A WELL-
ESTABLISHED POLEWARD OUTFLOW CHANNEL INTO A TROPICAL UPPER TROPO-
SPHERIC TROUGH (TUTT) CELL LOCATED AROUND 20N 170E. AS THE SYSTEM
IS TRACKING UNDERNEATH THE AXIS OF THE NEAR EQUATORIAL RIDGE, THERE 
IS ALSO GREAT EQUATORWARD OUTFLOW AND MINIMAL VERTICAL WIND SHEAR. 
TS 15W HAS TRACKED ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL 
RIDGE AT 08 KNOTS OVER THE PAST SIX HOURS. THE CURRENT INTENSITY IS 
BASED ON DVORAK ESTIMATES FROM PGTW (T3.O), KNES (T3.0) AND RJTD 
(JMA T2.5 EQUALS ABOUT 44 KNOTS). THE CURRENT POSITION IS SUPPORTED 
BY THE PGTW AND RJTD POSITION FIXES.
3. FORECAST REASONING.
    A. THE FORECAST PHILOSOPHY HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE THOUGH THE FORECAST INTENSITY HAS
BEEN INCREASED.
    B. TS 15W WILL CONTINUE TRACKING ALONG THE SOUTHERN PERIPHERY OF 
THE STEERING SUBTROPICAL RIDGE ANCHORED TO THE NORTHEAST. THE 
130000Z UPPER-LEVEL SOUNDING AT MINAMITORISHIMA (RJAM, 24.5N
154.0E) REPORTS EASTERLY WINDS THROUGHOUT THE COLUMN, CONFIRMING
THAT THE RIDGE IS STILL FIRMLY IN PLACE. THEREFORE, THE FORECAST
TAKES THE SYSTEM WESTWARD THROUGH TAU 24 BEFORE THE MID-LATITUDE
TROUGH CURRENTLY OVER JAPAN SLIGHTLY WEAKENS THE SUBTROPICAL RIDGE,
ALLOWING FOR A MORE NORTHWESTWARD TRACK BY TAU 48. IF THE TUTT CELL
TO THE NORTHEAST OF THE SYSTEM CONTINUES TO PUSH WESTWARD, THEN
TS CHOI-WAN WILL STEADILY INTENSIFY AS IT MOVES ALONG A FAVORABLE
ENVIRONMENT CHARACTERIZED BY LOW VERTICAL WIND SHEAR AND EXCELLENT 
OUTFLOW CHANNELS. 
     C. AFTER TAU 48 THE MID-LATITUDE TROUGH MENTIONED IN PARA 3.B
WILL LIFT TO THE NORTHEAST AND ENABLE TS 15W TO RESUME A NORTH-
WESTWARD TRACK ALONG A REORIENTED SUBTROPICAL RIDGE. AFTER TAU 96, A 
SECONDARY MID-LATITUDE TROUGH IS EXPECTED TO START TO BREAK DOWN THE 
SUBTROPICAL RIDGE ENOUGH TO ALLOW A GRADUAL RECURVE INTO THE MID-
LATITUDES. THE TIMING AND DEGREE OF THIS RECURVATURE (BEYOND TAU 
120) IS UNCERTAIN. AS THE ENVIRONMENT REMAINS FAVORABLE FOR 
DEVELOPMENT THROUGH TAU 120, THE SYSTEM IS EXPECTED TO INTENSIFY 
INTO A STRONG TYPHOON. THE BEST PERFORMING MODEL SOLUTIONS, SUCH AS 
ECMF, EGRR AND JGSM ARE IN STRONG AGREEMENT WITH THIS FORECAST 
SCENARIO. HOWEVER, THE SOLUTIONS PROVIDED BY THE GFS AND GFDN MODELS 
ARE DEPICTING A WEAKER SUBTROPICAL RIDGE AND QUICKER RECURVATURE 
SCENARIO TOWARDS IWO TO AFTER TAU 72. THIS FORECAST, AS WELL AS THE 
JTWC CONSENSUS, FAVORS THE BETTER PERFORMING MODELS THROUGH TAU 
120.//
NNNN