Tropical Storm KOPPU Advisory Sat Oct 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (KOPPU) WARNING NR 17//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 24W (KOPPU), LOCATED APPROXIMATELY 202 NM EAST-
NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 06 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
SHOWS THE SYSTEM HAS DEVELOPED A 13-NM EYE AS DEEP CONVECTIVE BANDS
WRAPPED TIGHTER INTO THE EYE. THE INITIAL POSITION IS BASED ON THE
EYE FEATURE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 105 KNOTS
IS BASED ON DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD AND REFLECTS
THE INTENSIFIED STATE OF THE TYPHOON. UPPER-LEVEL ANALYSIS INDICATES
THE SYSTEM REMAINS IN A HIGHLY FAVORABLE ENVIRONMENT WITH LOW
VERTICAL WIND SHEAR AND STRONG DUAL OUTFLOW. THE POLEWARD OUTFLOW
SURGED OVER THE LAST SIX HOURS, AS EVIDENT ON ANIMATED WATER VAPOR
IMAGERY. ADDITIONALLY, SEA SURFACE TEMPERATURES (SSTS) AT OVER 31
DEGREES CELSIUS IN THE PHILIPPINE SEA ARE HIGHLY CONDUCIVE FOR
FURTHER DEVELOPMENT. THE CYCLONE IS TRACKING ALONG THE SOUTHERN
PERIPHERY OF AN EXTENSION OF THE DEEP-LAYERED SUBTROPICAL 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 CONTINUE TO TRACK WESTWARD THROUGH TAU 24 ALONG
THE SOUTHERN PERIPHERY OF THE STEERING STR EXTENSION. UPPER-LEVEL
DYNAMICS AND SSTS WILL REMAIN FAVORABLE LEADING TO A PEAK INTENSITY
OF 120 KNOTS AT TAU 12. THE CYCLONE WILL MAKE LANDFALL AROUND TAU 24
NEAR CASIGURAN THEN RAPIDLY DECAY AS IT DRAGS THROUGH THE RUGGED
MOUNTAIN RANGES OF NORTHERN LUZON. AFTER TAU 24, TY 24W WILL TURN
POLEWARD AS THE STR EXTENSION RETREATS AND AN INDUCED RIDGE FORMS
BETWEEN TY 25W AND TY 24W AND ACTS AS THE WEAK PRIMARY STEERING
MECHANISM FOR THE REMAINDER OF THE FORECAST.
   C. IN THE EXTENDED FORECAST, TY KOPPU WILL EXIT INTO THE LUZON
STRAIT AT TROPICAL STORM STRENGTH AND CONTINUE TO TRACK NORTHWARD.
MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGH TAU 24, BUT
SIGNIFICANTLY SPREADS AFTERWARDS. IN VIEW OF THIS, THE JTWC TRACK
FORECAST CONFIDENCE LEVEL IS LOW.//
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