WDPN31 PGTW 260300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (TEMBIN) WARNING NR 29//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 15W (TEMBIN), LOCATED APPROXIMATELY 350 NM SOUTHWEST OF
TAIPEI, TAIWAN, HAS TRACKED SOUTH-SOUTHEASTWARD AT 04 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON A 252214Z SSMIS 
IMAGE AND RECENT RADAR FIXES FROM HONG KONG. THE CURRENT INTENSITY 
OF 85 KNOTS IS CONSISTENT WITH A 252332Z DVORAK T-NUMBER ESTIMATE 
FROM PGTW AND RECENT AUTOMATED INTENSITY FIXES. ANIMATED INFRARED 
SATELLITE IMAGERY SHOWS CONVECTION DEEPENING AROUND AN INCREASINGLY 
ORGANIZED, 20 NM EYE. A POLEWARD OUTFLOW CHANNEL HAS SUPPORTED 
INTENSIFICATION OVER THE PAST SIX HOURS. TY 15W IS TURNING EASTWARD 
UNDER THE STEERING INFLUENCE OF A NEAR-EQUATORIAL RIDGE CENTERED TO 
THE SOUTHEAST OF THE SYSTEM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY 15W WILL MOVE GENERALLY EASTWARD TO NORTHEASTWARD OVER THE 
UPCOMING 48 HOURS UNDER THE STEERING INFLUENCE OF THE NEAR-
EQUATORIAL RIDGE. THE PROJECTED NORTHEASTWARD TRACK WILL CARRY TY 
15W OVER TAIWAN BETWEEN TAU 48 AND TAU 72. PRIOR TO LANDFALL, LOW 
VERTICAL WIND SHEAR AND FAVORABLE POLEWARD OUTFLOW WILL ENABLE THE 
SYSTEM TO INTENSIFY, PARTICULARLY DURING THE NEXT 24 HOURS. LAND 
INTERACTION WITH THE MOUNTAINOUS TERRAIN OF TAIWAN SHOULD WEAKEN THE 
CYCLONE UNTIL IT REEMERGES OVER WATER TO THE NORTHEAST OF TAIWAN. 
   C. AFTER TAU 72, SUBTROPICAL RIDGING BUILDING IN THE WAKE OF TY 
16W WILL EXERT AN INCREASING INFLUENCE ON THE TRAJECTORY OF TY 15W 
AND IS EXPECTED TO NUDGE THE SYSTEM WESTWARD. THE EXACT TRACK OF TY 
15W DURING THE EXTENDED PERIOD REMAINS UNCERTAIN, DEPENDING UPON HOW 
QUICKLY THE SUBTROPICAL RIDGE BUILDS IN THE WAKE OF TY 16W AND HOW 
MUCH TY 15W WEAKENS DURING ITS TRANSIT ACROSS TAIWAN. IF THE 
SUBTROPICAL RIDGE BUILDS IN QUICKLY OR TY 15W WEAKENS MORE THAN 
FORECAST DUE TO LAND INTERACTION, THE SYSTEM WILL LIKELY FOLLOW A 
MORE WESTWARD TRACK INTO CENTRAL CHINA SOUTH OF SHANGHAI. DUE TO 
THESE UNCERTAINTIES, THERE IS LOW CONFIDENCE IN THE FORECAST TRACK, 
WHICH NOW LIES SLIGHTLY WEST OF THE MULTI-MODEL CONSENSUS NEAR THE 
ECMWF SOLUTION.//
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