Monitoring informs action
El Niño and La Niña are opposite phases of the El Niño–Southern Oscillation (ENSO); one of the most powerful naturally occurring climate patterns on Earth.
El Niño is characterized by a warming of ocean surface temperatures in the central and eastern Equatorial Pacific. It typically occurs every two to seven years and lasts around nine to twelve months.
It generally begins developing between March and June and reaches its peak intensity between November and February, with impacts on global temperatures typically being most pronounced in the second year after development.
The effects of each El Niño/La Niña event vary depending on the intensity, duration, time of year when it develops, and also how it interacts with other climate variability modes (such as the Indian Ocean Dipole). Not all regions of the world are affected, and even within a region, impacts can be different. Even when ENSO is neutral, extreme weather can still occur.
The strength of an ENSO event is highly significant – whether it is classed as weak, moderate, strong or very strong. Even a moderate El Niño makes some weather and climate extremes more likely.
WMO does not use the term “super El Niño” because it is not part of standardized operational classifications.
There is no evidence that climate change increases the frequency or intensity of El Nino events. But it can amplify associated impacts because a warmer ocean and atmosphere increases the availability of energy and moisture for extreme weather events such as heatwaves and heavy rainfall.
Typical impacts
Each El Niño event is unique in terms of its evolution, spatial pattern and impacts.
However, it is typically associated with increased rainfall in parts of southern South America, the southern United States, parts of the Horn of Africa and central Asia, and drier conditions over Central America, northern South America, the Caribbean, Australia, Indonesia, and parts of southern Asia.
During the Boreal summer, El Niño’s warm water can fuel hurricanes in the central/eastern Pacific Ocean, while it hinders hurricane formation in the Atlantic Basin. Thus, the US National Oceanic and Atmospheric Administration (NOAA) is forecasting a below-normal hurricane season for the Atlantic basin this year.
National Meteorological and Hydrological Services and WMO Regional Climate Centres and Regional Climate Outlook Forums issue regularly updated information to inform national and regional decision-making. WMO is also providing regular briefings to humanitarian agencies via the WMO Coordination Mechanism.
For example, the Greater Horn of Africa Climate Outlook Forum (GHACOF) predicts a high likelihood of below-normal rainfall across much of the northern Greater Horn of Africa during the critical June–September rainy season.
Similarly, South Asia is expected to receive below average monsoon rainfall, according to the South Asian Climate Outlook Forum.
The Central America region expects drier and warmer conditions according to the Central America Climate Outlook Forum.
Global Seasonal Climate Update
WMO also issued a complementary Global Seasonal Climate Update which takes into account ENSO and other key climate drivers, such as the North Atlantic Oscillation, the Southern Annular Mode and the Indian Ocean Dipole – which correlates closely with El Niño in the Pacific and which may develop into a positive phase, peaking concurrently with the intensifying El Niño.
For the June-July-August season, forecasts project a nearly universal dominance of above-normal temperatures in nearly all parts of the globe. These increase risks of heat stress and compounding hazards in some regions and accelerate the development of drought conditions where rainfall is reduced.
Rainfall probabilities are typical of El Niño patterns and this is likely to contribute to a greater probability of extremes (e.g. increased rainfall and flooding, as well as drier conditions and droughts.
