As a result, Pacific islands in the central Pacific region such as Kiribati, Nauru and Tuvalu may experience below normal rainfall which could lead to drought.
Islands in the South-West Pacific will experience higher than normal rainfall, such Fiji, Niue, Palau, Papua New Guinea, Samoa, Solomon Islands, Southern Cook Islands, Tonga and Vanuatu which might see flooding, landslides or possibly cyclones.
La Niña is expected to last right through to the first quarter of 2021.
The La Niña weather pattern is where the trade winds become stronger, enhancing the warm pool in the western Pacific and causing the sea surface temperatures in the Central and eastern Pacific become cooler.
La Niña is part of the El Nino Southern Oscillation, which is a major climate driver that influences normal rainfall, temperature, and sea level patterns across the Pacific.
"These phenomenon's may sound scientific, but the fact is that these terms and what they are will have direct impact on our lives in the Pacific," said Tagaloa Cooper, Director of Climate Change Resilience at SPREP.
"They will affect our food crops, our hygiene in the time of Covid-19, and our safety with the impacts of tropical cyclone season and floods or landslides in some parts of the region and potential drought in others," she said.
"We must all make an effort to know what is happening with our weather and climate and prepare ourselves for what may come, the more we can prepare, the more resilient we will be."
Multiple climate monitoring systems have all shown indications of the arrival of La Niña.
This month Australia's Bureau of Meteorology officially declared a La Niña, after changes in both sea surface temperature and atmospheric pressure was observed.