 For example, the Australian Bureau of Meteorology looks at the trade winds, SOI, weather models and sea surface temperatures in the Niño 3 and 3.4 regions before declaring that a La Niña event has started.However, the Japan Meteorological Agency declares that a La Niña event has started when the average five-month sea surface temperature deviation for the NINO.3 region is more than cooler for six consecutive months or longer.A timeline of all La Niña episodes between 1900 and 2019.