CNA Explains: What is El Nino and what can Singapore expect if it returns in 2026?

What is the Indian Ocean Dipole?

The IOD is similar to ENSO, but events occur in the equatorial Indian Ocean and have a shorter duration.

The IOD varies between three phases – positive, negative and neutral.

A positive IOD event, which suppresses cloud formation over certain parts of the tropical Indian Ocean, typically brings drier and warmer conditions to many parts of southern Southeast Asia.

“Singapore and our surrounding regions tend to experience drier conditions as sea surface temperatures in the eastern Indian Ocean are cooler, resulting in less cloud formation,” said MSS, noting that Singapore’s driest year on record occurred in 1997 when both El Nino and positive IOD events occurred.

When is an El Nino event declared?

Singapore monitors ENSO conditions using the Nino3.4 index, which averages sea surface temperature anomalies in the central-eastern equatorial Pacific Ocean.

According to the ASEAN Specialised Meteorological Centre, the threshold for an El Nino event in the Nino3.4 region is a figure of more than 0.65°C above normal, according to the index. The threshold for a La Nina event is a figure of more than 0.65°C below normal.

What is the impact of El Nino on the weather in Singapore?

During an El Nino event, Singapore and the surrounding region can expect hotter and drier weather.

“El Nino events tend to have the greatest influence on Singapore’s rainfall during the southwest monsoon season from June to September, increasing the chance of dry conditions,” the Met Service said.

“During the last strong El Nino event in 2015/2016, Singapore’s total rainfall from June to September 2015 was about 35 per cent below the long-term average.”

Temperatures will also rise during such an event.

“El Nino events also bring warmer temperatures to Singapore. Impact to temperatures is the highest during the period the El Nino event weakens, which is typically in March to May the year following the start of the event,” the Met Service said.

“During the decay of the last strong El Nino event in 2016, average temperatures in March (to) May were 29.2°C, or 1°C above the long-term average for that period.”

This made it Singapore’s second-warmest March-to-May period on record, with 2016 remaining one of Singapore’s hottest years on record, tied with 2019 and 2024, MSS added.

It is, however, difficult to predict exactly how hot and dry the weather could get in Singapore, said Associate Professor Xianfeng Wang of the Asian School of the Environment and Earth Observatory of Singapore at Nanyang Technological University.

“There are two factors that limit our predictability. One, we don’t know yet how strong the coming El Nino can be. And two, we also don’t know how the El Nino event may interact with other weather phenomena,” he told CNA.

“For example, the development of a positive Indian Ocean Dipole event may amplify the hot and dry conditions. On the other hand, the northeast monsoon later this year may relieve the harsh conditions a bit.”

Assoc Prof Wang said that climate models from international climate centres are currently showing a wide spread in predictions of how intense an El Nino event this year could be. However, “most of them do suggest it could be stronger than the 2023/2024 El Nino event”.

“We will have a better idea in the next couple of months, when more field observations can be available to calibrate climate model projections,” he added.

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