Tropical Storm KOPPU Advisory Tue Oct 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOPPU) WARNING NR
29//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 24W (KOPPU), LOCATED APPROXIMATELY 246 NM
NORTH-NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWARD AT 04
KNOTS OVER THE PAST SIX HOURS. ANIMATED MSI SHOWS A DISORGANIZED
SYSTEM THAT CONTINUES TO HUG THE LUZON COAST, WITH THE BULK OF THE
DEEP CONVECTION ON THE WESTERN SIDE OF THE RAGGED LLCC. A PREVIOUS
192008Z SSMIS IMAGE CONTINUES TO SHOW THE DEEP CONVECTION ON THE
WESTERN SIDE OF THE SYSTEM WITH LIMITED BANDING. DUE TO THE LOOSE
STRUCTURE OF THE LLCC, THERE IS LOW CONFIDENCE IN THE INITIAL
POSITION AND THE INTENSITY HAS BEEN DROPPED TO 50 KNOTS TO REFLECT
THE DISORGANIZED STRUCTURE OF THE SYSTEM. TS 24W REMAINS IN A
MARGINAL ENVIRONMENT WITH GOOD POLEWARD OUTFLOW WHICH ALMOST OFFSETS
THE 20+ KNOTS OF VWS. TS KOPPU IS TRACKING ALONG THE NORTHERN SIDE
OF A NER SOUTH OF THE SYSTEM AND AN INDUCED RIDGE BETWEEN TY 25W AND
TS 24W.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 24W WILL SLOWLY TRACK EAST-NORTHEASTWARD, NORTH OF LUZON
OVER THE NEXT 36 HOURS AS THE NER IS THE MAIN STEERING MECHANISM.
DUE TO CONTINUED LAND INTERACTION AND INCREASED VWS, THE SYSTEM WILL
SLOWLY DECREASE IN INTENSITY THROUGH TAU 36. BEYOND TAU 36, THE NER
WILL TRACK TO THE WEST, PROMOTING THE INDUCED RIDGE TO BECOME THE
MAIN STEERING MECHANISM, FORCING A POLEWARD COMPONENT TO THE TRACK.
ADDITIONALLY, THE SYSTEM WILL MAINTAIN ITS INTENSITY OF 40 KNOTS
THOUGH TAU 72 AS THE SLIGHTLY FAVORABLE INCREASED OUTFLOW WILL BE
OFFSET BY INCREASED VWS.
   C. IN THE EXTENDED TAUS, TS KOPPU WILL CONTINUE TO TRACK POLEWARD
ALONG THE WESTERN PERIPHERY OF THE BUILDING STR. THE SYSTEM WILL
CONTINUE TO SLOWLY WEAKEN AS IT ENCOUNTERS ADDITIONAL VWS BETWEEN
THE HIGHLY ZONALLY WESTERLIES TO THE NORTH AND THE STR TO THE EAST.
DYNAMIC MODEL GUIDANCE CONTINUE SO BE FAIRLY WIDELY SPREAD TRACKING
FROM THE EASTERN COAST OF TAIWAN TO EAST OF THE RYUKYU ISLAND CHAIN.
DUE TO THE COMPLEX STEERING ENVIRONMENT AND THE CONTINUED SPREAD OF
MODEL GUIDANCE, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK
WHICH IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS.//
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