Meteorological history Typhoon Koppu

map plotting track , intensity of storm, according saffir–simpson scale

a tropical disturbance formed in monsoon trough late on october 10, on enewetak atoll. 1 day later, japan meteorological agency (jma) upgraded low-pressure area tropical depression, yet low-level circulation center exposed owing strong vertical wind shear. on october 12, system kept consolidating convection sheared west, joint typhoon warning center (jtwc) issued tropical cyclone formation alert; half day after, jma started issue tropical cyclone warnings tropical depression. jtwc upgraded system tropical depression on october 13, although fragmented convective bands wrapping tighter broad llcc remained exposed. @ noon, tracking westward along southern periphery of deep-layered subtropical ridge, system intensified tropical storm , named koppu jma.

early on october 14, storm entered philippine area of responsibility , received name lando pagasa, , deepened convection obscured llcc late on same day, shortly before being upgraded severe tropical storm jma. under favorable environment of low vertical wind shear , radial outflow, koppu deepened rapidly , intensified typhoon in afternoon of october 15, when tightly-curved convective band wrapping eye revealed microwave imagery. intensification slowed down until apparent ragged eye formed 1 day later, sea surface temperature on 31 °c (88 °f) in philippine sea. 35 km (25 miles) eye became sharper on october 17, prompting jtwc upgrading koppu super typhoon one-minute maximum sustained winds @ 240 km/h (150 mph) in afternoon, equivalent category 4 of saffir–simpson hurricane wind scale. around 01:00 pht on october 18 (17:00 utc on october 17), koppu made landfall on casiguran, aurora in philippines; however, jma reported koppu reached peak intensity ten-minute maximum sustained winds @ 185 km/h (115 mph) , central pressure @ 920 hpa (27.17 inhg).

frictional effects land interaction luzon started erode typhoon rapidly after landfall, despite excellent dual outflow channels. before noon or in afternoon on october 18, koppu emerged south china sea disorganized system had begun encounter stronger easterly vertical wind shear. tracking northward along western periphery of extension of deep-layered subtropical ridge east-northeast, proximity luzon inhibiting system consolidating, leading jma downgrade koppu severe tropical storm when main convection had been sheared west on october 19. both jtwc , jma downgraded highly unorganized system ragged llcc tropical storm in afternoon. continuing hugging coast of luzon on october 20, koppu drifted northeastward , east-northeastward due embedded within weak complex steering environment near-equatorial ridge south , induced ridge between typhoon champi , koppu; convective organization hampered being embedded in mid-level trough along western periphery of subtropical ridge.