Typhoon Ketsana, known in the Philippines as Tropical Storm Ondoy, was the second-most devastating tropical cyclone of the 2009 Pacific typhoon season, causing $1.15 billion in damages and 665 fatalities, only behind Morakot earlier in the season, which caused 956 deaths and damages worth $6.2 billion. Ketsana was the sixteenth tropical storm, and the eighth typhoon of the season. It was the most devastating tropical cyclone to hit Manila, surpassing Typhoon Patsy (Yoling) in 1970.

The 2009 Pacific typhoon season was a below average season that spawned only 22 named storms, 13 typhoons, and five super typhoons. It was also recognized as the deadliest season in the Philippines for decades. The first half of the season was very quiet whereas the second half of the season was extremely active. The season's first named storm, Kujira, developed on May 3 while the season's last named storm, Nida, dissipated on December 3.