An ex-tropical cyclone climatology for Auckland, New Zealand

Auckland, New Zealand, is influenced by ex-tropical cyclones (ETCs); however, there is no established climatology for these weather systems at present. In this study, we present a climatology of ETCs for Auckland and investigate whether their spatio-temporal traits are influenced by large-scale climate modes such as the El Ni˜ no-Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). We utilize the South Pacific Enhanced Archive for Tropical Cyclone research (SPEArTC) to establish a climatology that covers the high-quality TC data period from 1970 to 2010. ETCs have entered a region within 550km of Auckland city regardless of ENSO or SAM phase, and on average one event per year occurs. Peak ETC season for Auckland is during March, preceded by an increase in activity during February, with a wide-range of meteorological impacts. Regional circulation patterns, including reduced blocking in the southwest Pacific and synoptic type presence, allow ETCs into the Auckland sector of the southwest Pacific while guiding them either to the east or west of the city.