Complex sentence: On September 20, the JTWC downgraded Malakas to a tropical storm, while the JMA downgraded it to a severe tropical storm, because at around 00:00 JST on September 20 (15:00 UTC on September 19), Malakas made landfall over the Ōsumi Peninsula in Japan.
Split into simpler sentences: On September 20, the JTWC downgraded Malakas to a tropical storm, while the JMA downgraded it to a severe tropical storm. At around 00:00 JST on September 20 (15:00 UTC on September 19), Malakas made landfall over the Ōsumi Peninsula in Japan.