The climate outlook up to April 2023 will likely see a rare occurrence of what is known as a three-peat La Nina event, where the El Nino Southern Oscillation (ENSO) status will be within La Nina thresholds for the third consecutive Tropical Cyclone season since the 2020-2021 TC season.
Climate models generally agree that this status is likely to remain through most of the TC season, and can have a significant impact on the climate of Samoa.
Although ocean observations in mid-2022 declined slightly to La Nina Alert levels, trade winds intensity increased there on after, resulting in an establishment of a La Nina in September 2022.
Sea surface and sub sea surface temperatures continue to show La Nina features in recent months, and according to seasonal outlook models, will continue on for most of the wet season.
The atmospheric indicators of ENSO are well within La Nina thresholds as well, which further supports the longevity of the La Nina phase to 2023.
Taking into consideration the current outlook status of ENSO, rainfall for the upcoming season is anticipated to be Normal to Above Normal conditions.
The impacts of La Nina vary from country to country, with the Melanesian countries (Solomon Islands, Vanuatu and New Caledonia) having higher than usual risks of tropical cyclones while countries such as Fiji and Polynesian neighbors in the eastern part of the South Pacific are likely to experience fewer than average tropical cyclones.
For Samoa, a La Nina event normally provides more rainfall than usual and a reduced number of tropical cyclones owing to the southwest displacement of the so-called birthplace of tropical cyclones known as the South Pacific Convergence Zone (SPCZ).
Potential Impacts Tropical cyclones are associated with torrential rainfall, flash flooding, flooding of low-lying areas, coastal flooding, storm surges, water spouts and strong to damaging winds.
Additionally, there is a high possibility for potential landslides and river flashing this coming season. Moreover, La Nina which is the positive phase of ENSO is sometimes known as the “opposite of El Nino”.
When a La Nina phase of ENSO strikes, it is generally associated with above-normal rainfall for Samoa which may lead to flooding of low-lying areas, higher than normal sea levels and increased potential of waterborne diseases due to flooding.
These events can cause loss of life and a great deal of damage to property.
The Samoa Meteorology Division will continue to closely monitor changes in the climate system and advise the public accordingly. Members of the public are urged to remain vigilant, alert and prepared throughout the 2022-2023 TC season and take heed of TC alerts, warnings and advisories issued.