 Towards the end of September , the monsoon trough spawned a tropical disturbance east @-@ northeast of Yap , which became a tropical depression on September 24 . There were initially several circulations , with a tropical upper tropospheric trough to the northeast increasing outflow . After slowing and turning to the northeast , the depression intensified into Tropical Storm Koppu on September 26 . After the storm developed a large eye feature , the JTWC upgraded it to typhoon status on September 27 , although the JMA did not follow suit until the following day while near Chichi @-@ jima . Also that day , Koppu passed 95 km ( 60 mi ) west of Iwo Jima , and the JMA estimated peak 10 minute winds of 130 km / h ( 80 mph ) . The JTWC estimated peak 1 minute winds of 165 km / h ( 105 mph ) , before an approaching trough caused the typhoon to accelerate northeastward . The convection diminished near the center , causing Koppu to become extratropical on September 30 . The remnants continued generally northeastward through the Aleutian Islands , eventually passing south of mainland Alaska on October 7 . 
 Towards the end of September , the monsoon trough<a href='been_done' title='1'><mark></mark></a> spawned a tropical disturbance east @-@ northeast of Yap , which became a tropical depression on September 24 . <a href='dey_it' title='2'><mark>There</mark></a> <a href='uninflect' title='3'><mark>were</mark></a> initially several circulations , with a tropical upper tropospheric trough to the northeast increasing outflow . After slowing and turning to the northeast , the depression intensified into Tropical Storm Koppu on September 26 . After the storm developed a large eye feature , the JTWC upgraded it to typhoon status on September 27 , although the JMA did not follow <a href='negative_concord' title='4'><mark>suit</mark></a> until the following day while near Chichi @-@ jima . Also that day , Koppu<a href='been_done' title='5'><mark></mark></a> passed 95 km ( 60 mi ) west of Iwo Jima , and the JMA estimated peak 10 minute winds of 130 km / h ( 80 mph ) . The JTWC estimated peak 1 minute winds of 165 km / h ( 105 mph ) , before an approaching trough caused the typhoon to accelerate northeastward . The convection diminished near the center , causing Koppu to become extratropical on September 30 . The remnants continued generally northeastward through the Aleutian Islands , eventually passing south of mainland Alaska on October 7 . 
Towards da end of September , the monsoon trough done spawned a tropical disturbance east @-@ northeast of Yap , which became a tropical depression on September 24 . It was initially several circulations , with a tropical upper tropospheric trough to tdanortheast increasing outflow . After slowing and turning to thdaortheast , thedapression intensified into Tropical Storm Koppu on September 26 . After the darm developed a bigass eye feature , the JTWC upgraded it to typhoon status on September 27 , although the Jdadid not follow no suit until the following day while near Chichi @-@ jima . Also that day , Koppu done passed 95 km ( 60 mi ) west of Iwo Jima , and the JMdastimated peak 10 minute winds of 130 km / h ( 80 mph ) . The JTWC estimated peak 1 minute winds of 165 km / h ( 105 mph ) , before an approaching trough caused the typhoon to accelerate northeastward . The condation diminished near the center , causing Koppu to become extratropical on September 30 . The remndas continued generally northeastward through the Aleutian Islands , eventually passing south of mainland Alaska on October 7 .