Complex sentence: Hester quickly became a typhoon and rapidly intensified into a Category 5 typhoon on the modern-day Saffir-Simpson hurricane wind scale on December 30 south of Guam.
Split into simpler sentences: Hester quickly became a typhoon and rapidly intensified. Near the end of the year, Hester became a Category 5 typhoon on the modern-day Saffir-Simpson hurricane wind scale south of Guam.