The scope of this article is limited to the Pacific Ocean, north of the equator between 100°E and the International Date Line.

Tropical storms that form in the entire Western Pacific basin are assigned a name by the Japan Meteorological Agency.

Tropical depressions that form in this basin are given a number with a "W" suffix by the United States' Joint Typhoon Warning Center.

In addition, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) assigns names to tropical cyclones (including tropical depressions) that enter or form in the Philippine area of responsibility.

For the PAGASA, 22 systems formed or entered in their area during 2009, which 12 of them directly made landfall over the Philippines.