El Niño back in the Pacific

The El Niño weather pattern is returning to the Pacific Ocean.

It usually brings drought conditions to the Asia-Pacific region, but wetter-than-usual weather to Latin America and the continental US, currently suffering its worst drought in 56 years. It causes wetter-than-normal weather in East Africa, including Kenya, Tanzania, and the White Nile basin.

Conversely, there are drier conditions from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique, South Africa and Botswana. In its latest climate outlook, New Zealand’s National Institute of Water and Atmosphere (Niwa) said that sea surface temperatures in the equatorial Pacific are warming, and tropical sea temperatures are near El Niño levels.

“Sea surface temperatures continue to warm in the equatorial Pacific, and tropical sea temperatures currently verge on the accepted El Niño threshold,” said Niwa. The majority of climate models it monitors predict El Niño will likely develop between August and October. However, Niwa said the Southern Oscillation remained close to zero in July, indicating the ocean-atmosphere feedbacks necessary for El Niño development are not yet fully in place.

Despite the looming El Niño, lower pressures to the north of New Zealand and higher pressures to the south are likely to dominate for the period between August and October. This means that the stronger-than-normal westerly spring winds often associated with El Niño periods aren’t expected to be very prominent during this period, said NIWA.

El Niño is defined by prolonged differences in Pacific Ocean surface temperatures when compared with the average.
This involves a warming of at least 0,5°C averaged over the east-central tropical Pacific Ocean. The first signs of El Niño are a rise in surface pressure over the Indian Ocean, Indonesia and Australia, and a fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean. The warm water spreads from the west Pacific and the Indian Ocean to the east Pacific, taking the rain with it and causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.