If British weather has always been unpredictable, 2026 seems determined to turn unpredictability into an art form.
We began the year with periods of persistent rain and saturated ground. Summer brought repeated heatwaves, drought conditions, wildfires and weeks when meaningful rainfall seemed to have gone missing. Then, towards the end of August, the conversation abruptly changed again, with thunderstorms bringing intense rainfall and the risk of localised flooding.
Now something potentially extraordinary is happening thousands of miles away.
The tropical Pacific Ocean is becoming unusually warm.
El Niño is back. And this one could be exceptional.
On 3 September, the World Meteorological Organisation said El Niño was now firmly established and expected to strengthen into a very strong event, with a near 100 per cent probability that El Niño conditions will persist through February 2027. Its latest multi-model forecast puts the average sea-surface temperature anomaly in a key part of the tropical Pacific at around 3.6°C above the relevant baseline during September to November.
The Met Office has gone further, describing the forecast signal as “unprecedented” and saying 2026 could produce the largest El Niño in living memory, and possibly the largest since the 19th century.
You may hear this described as a “super El Niño”.
But what exactly does that mean?
When the Atlantic comes calling: Britain’s weather is shaped by an extraordinary combination of influences stretching from the tropical Pacific to the North Atlantic. A powerful El Niño can alter the odds of wet and stormy conditions, but what Britain actually experiences depends on how those influences interact with the jet stream and other atmospheric systems.
And, perhaps more importantly for those of us looking out of a British window, what does unusually warm water in the Pacific Ocean have to do with whether we need an umbrella, a hosepipe or a snow shovel?
The answer takes us through an extraordinary planetary weather machine.
First, what exactly is El Niño?
El Niño is part of a natural climate cycle known as the El Niño Southern Oscillation, or ENSO.
Under normal conditions, trade winds blowing across the tropical Pacific help push warm surface water westwards towards Asia and Australia. During an El Niño event those winds weaken, allowing unusually warm water to spread eastwards across the central and eastern Pacific.
That might sound like a relatively local phenomenon.
It isn't.
The tropical Pacific contains an enormous amount of heat. Changing where that heat is concentrated changes where tropical rainfall and thunderstorms develop. That, in turn, alters atmospheric circulation.
Those disturbances can influence weather thousands of miles away through connections meteorologists call teleconnections.
El Niño isn't alone. Meteorologists monitor other climate drivers including the North Atlantic Oscillation, the Madden-Julian Oscillation, the stratospheric polar vortex and conditions across the Atlantic and Indian Oceans.
Our atmosphere, unsurprisingly, doesn't recognise national borders.
Something happening in the Pacific can ultimately influence the probabilities of particular weather patterns developing over the Atlantic and Europe.
But the important word is probabilities.
El Niño doesn't determine Britain's weather.
It loads one of the dice.
So what makes this El Niño different?
El Niño itself isn't unusual. It is a naturally occurring phenomenon and has been influencing the world's climate since long before industrialisation.
Its strength, however, varies considerably.
And the 2026 event is beginning to attract attention precisely because of how powerful it could become.
NOAA said in August that there was a greater than 90 per cent chance of a very strong El Niño during the Northern Hemisphere autumn and winter. More strikingly, it calculated a 69 per cent chance that the event during October to December could exceed the strength of any El Niño in its records dating back to 1950.
The latest WMO assessment is similarly remarkable. It expects El Niño to strengthen towards the end of 2026, with impacts continuing into 2027. The organisation warns that a very strong event can significantly alter rainfall and temperature patterns around the world, increasing risks from drought, flooding and extreme heat.
That doesn't mean everywhere experiences more extreme weather simultaneously.
Some regions become wetter.
Others become drier.
Some become warmer.
Storm tracks can change.
Agricultural conditions can shift.
And the strength of El Niño alone doesn't determine how severe the consequences will be in any individual country. Other oceans and atmospheric systems can reinforce, weaken or alter its influence.
That caveat becomes particularly important when we reach Britain.
How does the Pacific reach Britain?
From the Pacific to Britain: El Niño begins thousands of miles away, but changes in tropical rainfall can influence atmospheric circulation across the globe. By the time those signals reach the North Atlantic they interact with the jet stream, the North Atlantic Oscillation and ocean circulation. El Niño influences the probability of particular weather patterns. It does not determine the forecast.
There isn't an El Niño weather system that begins somewhere near Peru and eventually arrives over Portsmouth.
Instead, changing tropical rainfall alters enormous patterns of rising and sinking air. Those changes can send disturbances through the atmosphere, influencing circulation much farther north.
Eventually, some of those influences reach the North Atlantic.
But by then they are competing with numerous other forces.
And one of the most important is roaring several miles above our heads.
Britain's high-altitude weather conveyor belt
Around five to seven miles above the Earth's surface is a fast-flowing current of air called the jet stream.
It travels broadly from west to east and helps steer areas of high and low pressure.
When the jet stream is strong and positioned across the Atlantic towards Britain, low-pressure systems can follow it, bringing successive spells of wind and rain.
When it moves north, high pressure can dominate Britain instead.
And sometimes the jet stream buckles and meanders.
That's when weather patterns can become stuck.
A persistent area of high pressure can produce a beautiful summer day.
Then another.
And another.
Eventually, what began as pleasant weather becomes a heatwave. Without rain, soils dry, river flows fall and reservoirs decline. Vegetation dries sufficiently for wildfire risk to increase.
The reverse can happen too.
Low-pressure systems and rain-bearing fronts can become slow-moving, repeatedly soaking the same areas.
Sometimes the most important thing about extreme weather isn't simply how hot, wet or dry it becomes.
It's how long the pattern stays there.
Then there's the North Atlantic Oscillation
Another major influence has the rather intimidating name of the North Atlantic Oscillation, usually shortened to NAO.
Fortunately, the basic idea is simpler than its name.
The NAO describes differences in atmospheric pressure between the region around Iceland, where pressure is typically lower, and the Azores, where it is generally higher.
When that difference strengthens, producing what meteorologists call a positive NAO, Atlantic westerlies tend to strengthen too. Low-pressure systems are more readily driven towards Britain and northern Europe, often bringing wetter, windier conditions.
When the pattern weakens or reverses, blocking can become more likely.
So even with an extraordinarily powerful El Niño developing in the Pacific, what happens over Britain will still depend heavily upon what the atmosphere decides to do over the Atlantic.
This is why seasonal forecasting is about likelihood rather than certainty.
It can tell us that the dice are loaded.
It cannot tell us what number they will land on.
What about the Gulf Stream?
Then we reach one of the biggest pieces of the climate machine.
Britain sits much farther north than its generally mild climate might suggest. One reason is the enormous movement of heat through the Atlantic Ocean.
The Gulf Stream forms part of a much larger circulation system known as the Atlantic Meridional Overturning Circulation, or AMOC.
Scientists expect the AMOC to weaken as the climate changes. A complete collapse would have much more dramatic consequences, potentially including substantial regional cooling around the North Atlantic and major changes to rainfall patterns.
But weakening and collapse are not the same thing.
Nor does climate change mean Britain is inevitably heading towards dramatically colder winters.
The broader expectation remains that UK winters become warmer and wetter on average, while summers become hotter and drier.
AMOC nevertheless illustrates an important point.
Climate change doesn't mean every place simply gets warmer. It changes the distribution of heat through an extraordinarily complicated planetary system.
So where does climate change fit?
Perhaps the easiest way to understand all this is to imagine Britain's weather as a game of cards.
El Niño, La Niña, the NAO, the jet stream and other natural variations have always shuffled the deck.
They help determine whether Britain gets a wet winter, dry spring, cool summer or weeks of glorious sunshine.
Climate change is doing something different.
When the rain stays away: prolonged dry weather can rapidly expose the pressures on Britain’s water resources. Natural weather cycles continue to determine whether particular seasons are wet or dry, but they are now operating against a warmer background that can intensify evaporation, soil-moisture loss and drought stress.
It is changing the cards in the deck.
Natural variability hasn't disappeared.
A cold spell doesn't disprove global warming. A heatwave isn't automatically caused by climate change. Neither can every flood or drought simply be attributed to global warming because it occurred in a warmer world.
But today's weather is happening within an atmosphere and oceans containing more heat.
Warmer air can hold more water vapour. Higher temperatures increase evaporation and can intensify soil moisture loss. Warmer seas can provide additional energy and moisture to weather systems.
The natural cycles continue.
The background conditions against which they operate are changing.
And that's what makes the developing El Niño particularly fascinating.
We are about to watch one of the world's most powerful natural climate cycles play out against an already unusually warm global background.
Does that mean Britain faces an extreme winter?
Not necessarily.
And this is perhaps the most important point.
An exceptionally strong El Niño does not automatically mean an exceptionally extreme British winter.
The WMO itself stresses that the strength of an El Niño doesn't determine the severity of its effects in individual countries.
For Britain, the Pacific signal has to interact with the Atlantic.
The position of the jet stream matters. The NAO matters. Atlantic sea temperatures matter. The polar vortex and other atmospheric processes matter.
So headlines predicting precisely what Britain will experience months ahead should be treated cautiously.
Seasonal forecasting isn't really telling us whether it will snow in Birmingham on Christmas Day.
It is telling us whether particular types of weather have become more or less likely.
That's much less satisfying than a definitive forecast.
But it's much more useful.
Britain's weather isn't broken
After a year of saturated ground, heatwaves, drought, wildfires and sudden downpours, it is tempting to ask what has happened to British weather.
Perhaps the better question is what is happening to the system surrounding it.
El Niño will eventually fade.
At some point, La Niña will return.
The North Atlantic Oscillation will switch phases. The jet stream will wander north and south, occasionally behaving with the apparent determination to ruin a bank holiday.
Britain's weather will remain variable.
But those variations are now playing out against a background that is no longer stationary.
The oceans are warmer. The atmosphere is warmer. The water cycle is changing.
That matters whether we are managing reservoirs, designing drainage systems, fighting wildfires, farming the land or simply wondering what on earth to plant in the garden.
In our recent WaterMatters article, we asked how we build a garden capable of coping with both drought and intense rainfall.
The answer to why we increasingly need to ask questions like that lies partly in the Pacific, partly in the Atlantic, partly several miles above our heads and partly in the changing climate surrounding them all.
And now, with an El Niño developing that forecasters believe could be among the strongest we have ever observed, we are about to get an extraordinary demonstration of how those systems interact.
We don't yet know exactly what weather it will bring Britain.
That's rather the point.
The weather hasn't stopped being variable. The climate in which that variability happens has changed.
