WDPN31 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TEMBIN) WARNING NR 
37//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (TEMBIN), LOCATED APPROXIMATELY 125 NM 
SOUTH OF TAIPEI, TAIWAN, HAS TRACKED NORTHEASTWARD AT 15 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A 
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH STREAMING 
DEEP CONVECTION FLARING OVER THE SOUTHERN PORTIONS OF THE LLCC. 
RADAR IMAGERY FROM TAIWAN INDICATES THE LLCC IS BEGINNING TO EXPAND 
SLIGHTLY OVER THE PAST SIX HOURS, AND WEAKEN ALONG THE NORTHERN HALF 
OF THE SYSTEM. THE CURRENT INTENSITY OF 55 KNOTS HAS BEEN MAINTAINED 
BASED ON THE DVORAKS FROM PGTW REMAINING STEADY AT A 3.5/3.5 FOR THE 
PAST SIX HOURS. UPPER LEVEL ANALYSIS INDICATES TS 15W IS LOCATED TO 
THE SOUTHWEST OF AN ANTICYCLONE LOCATED OVER OKINAWA. UPPER LEVEL 
RIDGING EXTENDING FROM THE ANTICYCLONE OVER TAIWAN IS CREATING 
MODERATE LEVELS OF NORTHEASTERN VERTICAL WIND SHEAR (VWS) AND IS 
CAUSING THE DISLOCATION OF CONVECTION ALONG THE NORTHERN HALF OF THE 
SYSTEM. THERE IS HIGH CONFIDENCE IN THE POSITION BASED ON AVAILABLE 
RADAR DATA AND THE PARTIALLY EXPOSED LLCC. TS 15W IS TRACKING ALONG 
THE NORTHERN PERIPHERY OF A DEVELOPING NEAR EQUATORIAL RIDGE. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 15W IS FORECAST TO REMAIN ON A NORTHEASTWARD TRACK FOR THE 
NEXT 12 HOURS, TRANSITIONING TO A GENERAL NORTHWARD TRACK BEYOND TAU 
12 THROUGH TAU 72 AS A BUILDING SUBTROPICAL RIDGE (STR) TO THE EAST 
BECOMES THE DOMINANT STEERING INFLUENCE. THE INTENSITY IS EXPECTED 
TO DECREASE OVER THE NEXT 24 HOURS AS IMPACTS FROM THE PROXIMITY TO 
TAIWAN DISRUPTS LOW LEVEL INFLOW. BETWEEN TAU 24 AND 72 A SLIGHT 
INTENSIFICATION PERIOD IS EXPECTED AS THE SYSTEM REORGANIZES IN A 
FAVORABLE SURFACE ENVIRONMENT. THE UPPER LEVEL WILL REMAIN MARGINAL 
WHICH WILL LIMIT STRONGER INTENSIFICATION THROUGH TAU 48 WITH THE 
OVERALL ENVIRONMENT BECOMING LESS FAVORABLE BETWEEN TAU 48 AND 72 AS 
SEA SURFACE TEMPERATURES (SSTS) DECREASE AND VWS INCREASES. MODEL 
GUIDANCE IS IN GOOD AGREEMENT WITH THE FORECAST THROUGH TAU 48, BUT 
BEGINS TO SEPARATE SIGNIFICANTLY BY TAU 72. THERE IS HIGH CONFIDENCE 
IN THE TRACK THROUGH TAU 48, BUT BECOMES LOW CONFIDENCE BY TAU 72.
   C. DYNAMIC MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT OVER THE 
PAST SIX HOURS WITH THE MAJORITY SHOWING A SLIGHT SHIFT WESTWARD 
WITH THEIR RESPECTIVE SOLUTIONS SHOWING THE SYSTEM TRACKING INTO 
COASTAL NORTH KOREA, SIMILAR TO THE CURRENT TRACK OF TS 16W 
(BOLAVEN). THE CURRENT EXTENDED FORECAST REMAINS ALONG THE WESTERN 
SIDE OF THE ENVELOPE OF AVAILABLE MODEL GUIDANCE. THERE EXISTS 
SIGNIFICANT UNCERTAINTY WITHIN THE MODEL FIELDS REGARDING THE 
DEVELOPMENT OF THE DEEP LAYERED STR THAT IS EXPECTED TO STEER TS 15W 
AS TS 16W (BOLAVEN) MOVES INTO THE MID-LATITUDE FLOW. THE INTENSITY 
IS EXPECTED TO CONTINUE WEAKENING AS THE SSTS DECREASE AND VWS 
INCREASES. EXTRA-TROPICAL TRANSITION IS EXPECTED TO BEGIN BY TAU 96 
WITH COMPLETE TRANSITION BY TAU 120. BASED ON THE COMPLEX STEERING 
PATTERN AND LARGE SPREAD OF THE DYNAMIC MODELS IN THE EXTENDED TAUS, 
THERE IS LOW CONFIDENCE IN THE FORECAST TRACK BEYOND TAU 72.//
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