Tropical Storm KOPPU Advisory nie., 18.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (KOPPU) WARNING NR 22//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 24W (KOPPU), LOCATED APPROXIMATELY 100 NM NORTH-
NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
DEPICTS A DEEP CENTRAL DENSE OVERCAST FEATURE OBSCURING THE LOW
LEVEL CIRCULATION CENTER (LLCC). AN 180632Z SSMI 85GHZ MICROWAVE
IMAGE CONTINUES TO SHOW A MICROWAVE EYE FEATURE THAT SUPPORTS THE
INITIAL POSITION WITH GOOD CONFIDENCE AND PROVIDES EVIDENCE THAT THE
LLCC REMAINS OVER LAND. THE CURRENT INTENSITY HAS BEEN DECREASED TO
85 KNOTS BASED ON THE DETERIORATING STRUCTURE OF THE SYSTEM DUE TO
LAND INTERACTION AS THE SYSTEM TRACKS THROUGH CENTRAL LUZON. UPPER
LEVEL ANALYSIS INDICATES THAT THE SYSTEM REMAINS IN AN AREA OF LOW
VERTICAL WIND SHEAR (VWS) AND EXCELLENT DUAL OUTFLOW CHANNELS.
HOWEVER, FRICTIONAL EFFECTS CAUSED BY THE RUGGED TERRAIN ARE CAUSING
THE RAPID WEAKENING OF THE SYSTEM. TY 24W IS TRACKING ALONG THE
SOUTHERN PERIPHERY OF AN EXTENSION OF THE DEEP-LAYERED SUB-TROPICAL
RIDGE (STR) TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 24W WILL TRACK ALONG THE SOUTHWESTERN PERIPHERY OF THE STR
OVER THE NEXT 12 HOURS PRIOR TO TURNING POLEWARD. THE CYCLONE WILL
TRACK POLEWARD AT A VERY SLOW PACE DUE TO A COMPETING STEERING
MECHANISM FROM A SECONDARY STR TO THE WEST. TY KOPPU WILL CONTINUE
TO WEAKEN DUE TO LAND INTERACTION AS IT MOVES ALONG THE WESTERN
COAST OF LUZON. JUST BEFORE TAU 72, TY KOPPU WILL RE-EMERGE OVER
WATER IN THE LUZON STRAIT AT TROPICAL STORM INTENSITY.
   C. IN THE EXTENDED TAUS, TY KOPPU WILL TRACK NORTHWARD AT A
SLIGHTLY FASTER PACE AS AN EXTENSION OF THE STR BUILDS IN NORTHEAST
OF THE SYSTEM. THE TYPHOON WILL BEGIN TO RE-INTENSIFY AS LOW VWS,
GOOD OUTFLOW, AND WARM SSTS PREVAIL, REACHING 60 KNOTS BY THE END OF
THE FORECAST PERIOD. DYNAMIC MODEL GUIDANCE SHOWS A BIFURCATION DUE
TO THE EXTENT OF THE STEERING STR WITH GFS, COAMPS-TC, AND HWRF
TRACKING THE SYSTEM WESTWARD TOWARDS HONG KONG AND THE BULK OF THE
GUIDANCE TRACKING THE SYSTEM NORTH TOWARDS TAIWAN. DUE TO THE
CONTINUED SPREAD IN MODEL SOLUTIONS AND THE CHALLENGING STEERING
ENVIRONMENT, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC FORECAST
TRACK WHICH IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS.//
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