Sarika was first noted by the United States-based Joint Typhoon Warning Center (JTWC) as a disorganized tropical disturbance on Octoberxa011, while it was about  southeast of Manila. The system quickly consolidated within a favorable environment of low wind shear and high sea surface temperatures of about , leading the JTWC to issue a Tropical Cyclone Formation Alert. By 00:00xa0UTC on Octoberxa013, the systems low-level circulation center became increasingly symmetric as it tracked northwestwards and the Japan Meteorological Agency (JMA) upgraded the disturbance to a tropical depression. The JTWC followed suit six hours later. Intensification slowed thereafter as an upper-level anticyclone suppressed outflow on the eastern side of the system. However, the system managed to intensify into a tropical storm by 18:00xa0UTC on Octoberxa013 as it traveled west-northwestwards along a subtropical ridge. At this point, the system was given the name Sarika by the JMA. The Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA), which had been tracking the storm since Octoberxa012, assigned it the local name Karen.