circulation with a good outflow. The JMA later recognized the same area of convection as a tropical depression on October 9. At 14:00 UTC the same day, the JTWC issued a TCFA for the invest as it developed a flaring convection which was circulating over the obscured LLCC. By midnight of the next day, the JMA upgraded it to a tropical storm and named it Namtheun. The JTWC recognized it as a tropical depression, three hours later, and six hours later, the JTWC upgraded it to a tropical storm. Namtheun managed to maintain its intensity for two days, until at 09:00 UTC of October 13, it was downgraded to a tropical depression by the JTWC, as it started moving westwards because of the presence of a subtropical ridge towards the southeast of the system. Satellite imagery showed that the deep convection had been displaced towards the northeast and the LLCC of the system had become less defined. However at 15:00 UTC of the next day, the JTWC re-upgraded it to a tropical storm, as it entered over warm sea-surface temperatures which allowed the system to maintain its intensity despite high wind shear. Satellite imagery also indicated that it developed subtropical characteristics. Unexpectedly, Namtheun further intensified into a severe tropical storm according to JMA at 06:00 UTC of October 16, and a Category 1-equivalent typhoon according to JTWC at 09:00 UTC of October 16. Satellite imagery depicted that the system had developed a compact core with improved convection structure near its center. It also developed an eye-like feature. The weakening of the vertical wind shear was main reason for the intensification and also the presence of marginally favorable sea-surface temperatures (). A few hours later, both JMA and JTWC downgraded to a tropical storm, as its convection had weakened significantly because of further cooling of sea-surface temperatures and strengthening of the wind shear. Namtheun managed its intensity as it continued north-northwards but since it was interacting with the baroclinic zone, it started its extratropical transition between 00:00 and 15:00 UTC. For the next several days, the system moved eastward across the North Pacific, before undergoing explosive intensification and developing into a bomb cyclone on October 21, reaching an extratropical peak of , while situated off the coast of the Pacific Northwest. Afterward, the system curved northward and then north-northwestward, while gradually weakening, before being absorbed into another approaching extratropical cyclone from