For the third year in a row the World Meteorological Organisation (WMO) has de-clared a La Niña in the Pacific.
The warning means the trad-itional weather pattern will be disrupted, with some parts being drier than normal while others can expect flooding.
It is the first time since the 1950s that such weather patterns have occurred three years in a row.
Dr Simon McGree, of the Aust-ralia Bureau of Meteorology, said people needed to heed warnings of weather changes in their regions.
“La Niña is a normal part of our climate system. El Niño and La Niña events swing back and forth every three to seven years on average but recently we have seen a series of three La Niña events, which is very unusual,” he said.
La Niña refers to the large-scale cooling of the ocean temperatures in the central and/or eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely wind, pressure and rainfall.
During La Niña Pacific countries in the west, including Palau, mainland Papua New Guinea,
Solomon Islands, New Caledonia, Vanuatu, Fiji, Tonga, Wallis and Futuna, Samoa, American Samoa, Niue, southern Cook Islands and southern French Polynesia tend to receive higher than normal rainfall.
The opposite impact is ex-perienced in countries in the central Pacific.
These include Nauru, Kiribati, Tuvalu, Tokelau, northern Cook Islands and northern French Polynesia.
Experts are warning of a risk of water borne diseases in some places, possible drought and shortage of water in others.
Infrastructure, crops and live-stock, and food security generally could be under threat.
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