WDPN31 PGTW 181500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W WARNING NR 08//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. REMARKS: TROPICAL STORM 06W, LOCATED 230 NM EAST OF MANILA, 
PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 10 KNOTS DURING THE PAST 
SIX HOURS. ANIMATED INFRARED IMAGERY SHOWS TS 06W IS STILL 
STRUGGLING AGAINST THE COMBINED EFFECTS OF VERTICAL WIND SHEAR (VWS) 
AND SUPPRESSED POLEWARD OUTFLOW. ANIMATED WATER VAPOR IMAGERY 
REVEALS AN EXTENSIVE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) ALONG 
THE 20TH LATITUDE, WHICH IS PRODUCING SUBSIDENCE TO THE NORTH OF THE 
STORM. AN 180929Z 37 GHZ SSMIS IMAGE SHOWS THE MAJORITY OF LOW LEVEL 
BANDING IS OVER THE WESTERN SEMICIRCLE OF THE STORM, WHICH SUGGESTS 
THAT VWS IS HIGHER THAN ANTICIPATED  BY GUIDANCE. RECENT INFRARED 
ANIMATION DOES SHOW SOME COOLING CLOUD TOPS AND A BURST OF 
CONVECTION NEAR THE LOW LEVEL CIRCULATION CENTER (LLCC). THE CURRENT 
INTENSITY ANALYSIS IS BASED ON AN AVERAGE OF DVORAK ESTIMATES FROM 
PGTW, KNES, AND RJTD, AND IS SUPPORTED BY SHIP AND LAND REPORTS 
PROXIMAL TO THE SYSTEM. TS 06W IS STEERING ALONG THE SOUTHWESTERN 
PERIPHERY OF THE SUBTROPICAL RIDGE TOWARDS AN AREA OF DECREASING VWS 
AND FAVORABLY DIFFLUENT FLOW ALOFT.
3. FORECAST REASONING.
   A. THERE IS A SLIGHT REDUCTION IN THE INTENSITY FORECAST DUE TO 
THE SLOWER THAN EXPECTED RATE OF DEVELOPMENT, BUT OTHERWISE THERE 
ARE NO SIGNIFICANT CHANGES TO THE FORECAST PHILOSOPHY. 
   B. NORTHWESTWARD MOVEMENT ALONG THE SOUTHWESTERN PERIPHERY OF THE 
SUBTROPICAL RIDGE WILL CONTINUE FOR THE NEXT 48 HOURS. TS 06W WILL
CONTINUE A SLOW YET STEADY INTENSIFICATION TREND DUE TO THE 30-31 
DEGREE WATERS, FAVORABLE EQUATORWARD OUTFLOW, AND DECREASING 
VERTICAL WIND SHEAR ALONG ITS TRACK. IN THE NEAR TERM, TS 06W WILL 
ALSO GET A BOOST TO POLEWARD OUTFLOW AS IT APPROACHES THE TUTT, BUT 
AS THE SYSTEM MOVES INTO THE LUZON STRAIT THE SUBSIDENCE ASSOCIATED 
WITH THE TUTT WILL SUPPRESS OUTFLOW AND BEGIN TO WEAKEN THE SYSTEM. 
THIS WEAKENING PROCESS IS EXPECTED TO BEGIN BY TAU 48 AND WILL 
COINCIDE WITH FALLING OCEAN HEAT CONTENT VALUES. MODEL GUIDANCE IS 
SPLIT, WITH NOGAPS/GFDN/WBAR TRACKING THE SYSTEM INTO EXTREME 
NORTHEASTERN LUZON, AND ECMWF, EGRR, AND JGSM MOVING THE SYSTEM 
TOWARDS SOUTHERN TAIWAN. BASED ON THE INTENSITY OF THE ANTICYCLONE 
PLANTED OVER EASTERN CHINA, THE MID-RANGE FORECAST STAYS RIGHT OF 
CONSENSUS, FAVORING ECMWF AND JGSM OVER NOGAPS/GFDN AND WBAR. 
   C. IN THE EXTENDED RANGE, LOWER OCEAN HEAT CONTENT, RESTRICTED 
OUTFLOW ALOFT, AND INCREASING VERTICAL WIND SHEAR FROM THE NORTHEAST 
WILL WEAKEN THE CYCLONE. TS 06W WILL BEGIN WEAKENING OVER WATER 
NORTH OF 20 DEGREES NORTH LATITUDE. THE PRIMARY STEERING MECHANISM 
THROUGH THE LONG RANGES WILL BE THE SOUTHWESTERN PERIPHERY OF THE 
SUBTROPICAL RIDGE. THE EXTENDED FORECAST HEDGES CONSENSUS TOWARDS 
ECMWF AND JGSM.//
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