El Niño is often associated with heavy rains, floods and disruption, but the phenomenon begins thousands of kilometres away from Kenya, in the tropical Pacific Ocean.
At its simplest, El Niño is a large-scale warming of the tropical Pacific that alters the normal relationship between the ocean and the atmosphere.
It is part of the El Niño-Southern Oscillation (ENSO), a natural climate pattern that shifts between El Niño, neutral and La Niña phases.
But what causes the Pacific Ocean to warm, and why can that change weather patterns in Kenya?
Under normal conditions, strong easterly trade winds blow across the tropical Pacific from the coast of South America towards Indonesia and Australia.
These winds push warm surface water towards the western Pacific while allowing colder water from deeper in the ocean to rise in the east, a process known as upwelling.
During El Niño, the trade winds weaken. With less wind pushing the warm water westwards, it begins moving eastwards across the Pacific.
Consequently, the surface of the central and eastern Pacific becomes warmer than normal.
The change in ocean temperatures then feeds back into the atmosphere, altering patterns of rising air, pressure, clouds and rainfall.
This ocean-atmosphere interaction is the engine behind El Niño.
The warming of the Pacific does not simply remain over the ocean. It changes large-scale atmospheric circulation, including the Walker circulation, which normally helps distribute heat and moisture across the tropics.
Once that circulation is disturbed, rainfall and temperature patterns can shift across distant parts of the world.
That is why El Niño does not produce the same weather everywhere. Its effects depend on the strength and timing of the event, the season and other atmospheric and oceanic conditions.
Scientists also cannot assume that every El Niño will produce identical impacts.
The National Oceanic and Atmospheric Administration (NOAA) notes that the location, strength and structure of Pacific warming vary from one event to another, while normal atmospheric variability also influences the resulting weather.
The developing 2026 event is now attracting particular attention because international forecasts point to a potentially significant El Niño.
The World Meteorological Organisation says there is an 80 per cent likelihood of El Niño conditions during June-August 2026, with the probability of the event continuing until at least November near or above 90 per cent.
Although uncertainty remains over its peak strength and timing, most forecast models suggest the event will be at least moderate and possibly strong.
For Kenya, the concern is not simply whether El Niño exists, but how its influence interacts with the country’s own weather patterns.
The government has classified 18 of Kenya’s 47 counties as being at high risk as preparations intensify for the anticipated rains.
The potential consequences include flooding in vulnerable areas, damage to roads and other infrastructure, disruption of livelihoods and pressure on communities living in flood-prone locations.
Kenya’s weather, however, will not be uniform.
The Kenya Meteorological Department’s June-July-August (JJA) 2026 Seasonal Forecast, issued on May 30, points to near-average to below-average rainfall over the Highlands West of the Rift Valley, Lake Victoria Basin, Rift Valley and Northwestern Kenya.
The Coast is expected to receive near-average to above-average rainfall.
The Highlands East of the Rift Valley, including Nairobi, some parts of the Southeastern lowlands neighbouring Nairobi and a few high-ground areas of Marsabit and Taita Taveta counties, are expected to experience occasional cool and cloudy conditions with light rains.
Most of the Southeastern lowlands and the Northeastern region, meanwhile, are expected to remain generally sunny and dry.
Mean temperatures are forecast to be warmer than average over most parts of the country.
The more consequential rainfall outlook will emerge as Kenya approaches the October-November-December season, traditionally an important rainfall period for many parts of the country.
The Met Department says there is a near or above 90-96 per cent probability that the anticipated El Niño-related rains will affect the country and continue through the end of 2026.
The department has cautioned that the forecasts will be refined as more observations become available.
“KMD will issue the national October-November-December (OND) 2026 seasonal forecast in late August/early September 2026,” acting director Edward Muriuki said.
He added that the department remains committed to providing timely weather and climate information to safeguard lives, livelihoods and property through proactive planning and coordinated response measures.
“Members of the public are encouraged to stay informed through official weather updates and advisories. Further information will be issued as forecasts are refined and additional information becomes available,” he said.
Understanding El Niño is important because it is not a rain-making switch that can simply be turned on over Kenya.
It is a chain of interactions beginning with the Pacific Ocean, involving winds, ocean temperatures and atmospheric circulation, before influencing weather patterns far beyond the region where it develops.
For Kenya, El Niño does not occur in isolation. Kenya Met is also closely monitoring the Indian Ocean Dipole (IOD) signal, which modulates the occurrence of El Niño in the country.
The IOD, which Met said is currently neutral, is a natural climate pattern defined by the difference in sea-surface temperatures between the western and eastern tropical Indian Ocean.
It alters winds, clouds, and rainfall across Africa, Asia, and Australia.
“The combined effects of El Niño and a positive IOD significantly influence rainfall patterns over Kenya, potentially leading to enhanced rainfall during the October-November-December (OND) season,” Muriuki said.
The eventual impact will depend not only on how strong the El Niño becomes, but also on where and when rainfall occurs, how long it lasts and the ability of communities and authorities to respond to extreme weather.
