 In the middle of October , an area of convection persisted along the monsoon trough between Luzon and Guam , developing into a tropical depression on October 17 . The same monsoon trough later spawned Typhoon Parma to the east . For several days , the system remained disorganized while drifting to the west @-@ northwest due to weak steering currents south of the subtropical ridge . On October 19 , the JMA upgraded the depression to Tropical Storm Ketsana , and by that time the storm had begun drifting to the northeast . With favorable outflow , Ketsana quickly intensified into a typhoon on October 20 after developing an eye , and two days later , the JMA estimated peak winds of 165 km / h ( 105 mph ) . The JTWC estimated peak 1 minute winds of 230 km / h ( 145 mph ) around the time the well @-@ defined eye had expanded to 37 km ( 23 mi ) . Subsequently , the typhoon accelerated northeastward into the westerlies and began weakening due to increasing wind shear and dry air . On October 26 , Ketsana became extratropical to the east of Japan and dissipated the next day . The passage of the typhoon caused surface chlorophyll a concentration in the ocean to increase 30 @-@ fold . 
 In the middle of October , an area of convection persisted along the monsoon trough between Luzon and Guam , developing into a tropical depression on October 17 . The same monsoon trough later spawned Typhoon Parma to the east . For several days , the system remained disorganized while drifting to the west @-@ northwest due to weak steering currents south of the subtropical ridge . On October 19 , the JMA upgraded the depression to Tropical Storm Ketsana , and by that time the storm <a href='been_done' title='1'><mark>had</mark></a> begun drifting to the northeast . With favorable outflow , Ketsana quickly intensified into a typhoon on October 20 after developing an eye , and two days later , the JMA estimated peak winds of 165 km / h ( 105 mph ) . The JTWC estimated peak 1 minute winds of 230 km / h ( 145 mph ) around the time the well @-@ defined eye <a href='been_done' title='2'><mark>had</mark></a> expanded to 37 km ( 23 mi ) . Subsequently , the typhoon accelerated northeastward into the westerlies and began weakening due to increasing wind shear and dry air . On October 26 , Ketsana became extratropical to the east of Japan and<a href='been_done' title='3'><mark></mark></a> dissipated the next day . The passage of the typhoon caused surface chlorophyll a concentration in the ocean to increase 30 @-@ fold . 
In the middle of October , an area of convection persisted along the monsoon trough between Luzon and Guam , developing into a tropical depression on October 17 . The same monsoon trough later spawned Typhoon Parma to the east . For several days , the system remained disorganized while drifting to the west @-@ northwest due to weak steering currents south of da subtropical ridge . On October 19 , the JMA upgraded tdadepression to Tropical Storm Ketsana , and by that time thdatorm done begun drifting to the northeast . With favorable outflow , Ketsana quickly intensified into a typhoon on October 20 after developing an eye , and two days later , the JMA estimated peak winds of 165 km / h ( 105 mph ) . The JTWC estimated peak 1 minute winds of 230 km / h ( 145 mph ) around the time the well @-@ defined eye done expanded to 37 km ( 23 mi ) . Subsequently , thedaphoon accelerated northeastward into the westerlies and began weakening due to increasing wind shear and dry air . On October 26 , Ketsana became extratropical to the east of Japan and been dissipated the dat day . The passage of the typhoon caused surface chlorophyll a concentration in the odan to increase 30 @-@ fold .