Subtropical Cyclone Katie, unofficially named by researchers, was an unusual weather event in early 2015. After the 2014–15 South Pacific cyclone season had officially ended, a rare subtropical cyclone was identified outside of the basin near Easter Island, during early May, and was unofficially dubbed Katie by researchers. Katie was one of the few tropical or subtropical systems ever observed forming in the far Southeast Pacific, outside of the official basin boundary of 120°W, which marks the eastern edge of RSMC Nadi's and RSMC Wellington's warning areas, during the satellite era. Due to the fact that this storm developed outside of the official areas of responsibility of the warning agencies in the South Pacific, the storm was not officially included as a part of the 2014–15 South Pacific cyclone season. However, the Chilean Navy Weather Service issued High Seas Warnings on the system as an extratropical low.

The 2014–15 South Pacific cyclone season was a slightly-below average tropical cyclone season, with five tropical cyclones occurring within the basin between 160°E and 120°W. The season officially ran from November 1, 2014, to April 30, 2015. During the season, tropical cyclones were officially monitored by the Regional Specialized Meteorological Center (RSMC) in Nadi, Fiji and the Tropical Cyclone Warning Centers in Brisbane, Australia and Wellington, New Zealand. The United States Armed Forces through the Joint Typhoon Warning Center (JTWC) also monitored the basin and issued unofficial warnings for American interests. RSMC Nadi attaches a number and an F suffix to tropical disturbances that form in or move into the basin while the JTWC designates significant tropical cyclones with a number and a P suffix. RSMC Nadi, TCWC Wellington and TCWC Brisbane all use the Australian Tropical Cyclone Intensity Scale and estimate windspeeds over a period of ten minutes, while the JTWC estimated sustained winds over a 1-minute period, which are subsequently compared to the Saffir–Simpson hurricane wind scale (SSHWS).