The season officially started on May 15, 1991 in the Eastern Pacific—designated as the area east of 140°W—and on June 1, 1991 in the Central Pacific, which is between the International Date Line and 140°W.

These dates typically limit the period of each year when most tropical cyclones form in the eastern Pacific basin.

This timeline documents all the storm formations, strengthening, weakening, landfalls, extratropical transitions, as well as dissipation.

Delores, Ignacio and Marty threatened the coast of Mexico, coming close enough to require tropical cyclone watches and warnings.

Public advisories were issued for four other systems due to the threat of heavy rain along the Mexican coast.