The tropical Pacific Ocean’s sea surface temperature (SST) anomalies remained in La Niña conditions in January 2018 (Figure A). Atmospheric indicators of El Niño/La Niña (e.g. trade winds and the Southern Oscillation Index, SOI) showed patterns indicative of La Niña conditions. The 1-month Nino3.4 value for January 2018 was -1.1, while the 3-month average (November 2017 to January 2018) Nino3.4 was at -1.0 which is in the weak to moderate La Niña range (Figure B). Partial data in February 2018 show weekly SST anomalies plateauing or warming slightly.
Models suggest the tropical Pacific Ocean will remain cooler than average but gradually warming to neutral in the 2nd quarter of 2018 (Figure C). Models indicate around 60% chance of La Niña conditions to last up to the February-April 2018 season (Figure D).
Impact of El Niño/La Niña on Southeast Asia
Typically the impact from La Niña for Southeast Asia is wetter-than-normal rainfall conditions, especially during the Southwest Monsoon period (June – September), including October (Figure E) and especially over the Maritime Continent. During El Niño events the opposite, i.e. drier-than-normal conditions, normally occurs. For November – January season, the impact of El Niño/La Niña is less coherent for some part of the region example over mainland Southeast Asia, Borneo, Southern Sumatra, and Malay Peninsula (Figure F). Locally-specific impact differs from place to place and for different seasons.
No two El Niño events or two La Niña events are alike in terms of their impact on the region’s rainfall and temperature. Furthermore, the strength of events and the corresponding impact do not always scale. For example, there were years where relatively weaker El Niño/La Niña events induced more significant changes in rainfall than the stronger events.
El Niño/La Niña
For El Niño/La Niña updates, ASMC assesses information provided by the World Meteorological Organization (WMO) and various international climate centres, such as the Climate Prediction Center (CPC) US, the Bureau of Meteorology (BoM) Australia, as well information from the International Research Institute for Climate and Society (IRI) which has model outputs from various other centres around the world.
Frequently Asked Questions
What is El Niño/La Niña and how do they affect weather in South East Asia?
The El Niño phenomenon is a non-regular occurrence in the tropical pacific region where warmer waters develop over the Eastern Tropical Pacific Ocean along the coast of South America. In South East Asia, this brings drier weather and increases the risk of forest fires and smoke haze. The La Niña phenomenon is the reverse of the El Niño where cooler waters develop over the Eastern Tropical Pacific Ocean along the coast of South America.
In South East Asia, higher than normal rainfall tends to occur during a La Niña episode which may result in an increased occurrence of floods.
The correlation between El Niño/La Niña and its associated weather impacts on South East Asia differ from one place to another and for different seasons.
The image above shows the precipitation anomalies averaged over the El Niño and La Niña years. For instance, the impact of El Niño is typically stronger over the southern and eastern part of South East Asia during the months of Jun – Oct.