ByBen RichLead Weather Presenter and Simon King Lead Weather Presenter

The developing El Niño climate phenomenon is now the strongest on record, according to scientists monitoring Pacific Ocean temperatures.

Daily sea surface temperatures in a key region of the central-eastern Pacific were 3.05C above average on 19 September - exceeding the previous record of 3.02C set during the very strong El Niño of 2015.

Some longer-term measures of El Niño have not yet hit record levels but this is likely to change, with the peak not expected until later this year.

El Niño can cause major shifts in weather patterns around the world, with the Met Office saying many of the expected impacts are already being felt.

What is El Niño and how is it measured?

El Niño is a naturally-occurring pattern, which happens about every two to seven years and tends to last for around a year.

Trade winds that typically blow from east to west across the Pacific Ocean can weaken or even reverse, allowing warm water to spread eastwards.

Heat is then released from the ocean into the atmosphere which can boost global temperatures and drive changes in weather patterns around the world.

Forecasters track the development of El Niño by watching temperatures in a key region of the Pacific Ocean. When these are consistently 0.5C above normal, an El Niño is declared.

There are different ways of measuring the strength of El Niño, however.

The records that have now been broken relate to daily measurements of sea surface temperature compared with the long term historical average.

This is called the Oceanic Niño Index (ONI).

Many scientists - including forecasters in the USA and Australia - also consider an alternative measure known as the Relative Oceanic Niño Index (RONI).

This measures how warm the key El Niño region is relative to the rest of the tropical oceans, meaning it takes into account the background warming caused by climate change.

By the RONI index the current El Niño is not yet a record-breaker - but it is likely that more announcements will follow in the coming weeks.

Professor Adam Scaife, Head of Long Range Prediction at the Met Office, said: "We have been signalling for months that the developing El Niño will be an unprecedented event.

"The fact that it has already exceeded previous records – with several weeks to go before it peaks later this year – shows the enormity of this El Niño."

Impacts of El Niño already being felt globally

Every El Niño is different, therefore impacts on global weather patterns are not guaranteed.

And the unprecedented strength of this El Niño does not necessarily mean it will have unprecedented impacts on the weather.

Professor Scaife said: "Scientists are still assessing whether the impacts will be in proportion to its magnitude, but we are already seeing expected effects worldwide."

El Niño increases the odds of storms and floods in some regions and of drought and wildfires in others.

El Niño years tend to bring below-average monsoon rainfall in India, which is already being reflected in this year's data.

Statistics from the India Meteorological Department show that, until 22 September the southwest monsoon had brought 15% less rain than normal.

Another typical impact of El Niño is reduced hurricane activity in the Atlantic due to changes in wind patterns high in the atmosphere.

So far in 2026 there have been no Atlantic hurricanes, setting a new record for the latest date without a hurricane forming since satellite monitoring of storms began.

Other possible effects - some of which are already being felt - include the increased risk of floods in coastal parts of Ecuador, Peru and the southern USA, and the enhanced threat of drought and wildfires in Brazil, Australia and Indonesia.

These weather impacts can have significant knock on effects for on crop yields, food security and economies around the globe.

Will there be an impact on UK weather?

The UK is thousands of miles from the tropical Pacific and so the effects of El Niño tend to be less clear-cut than in other regions.

However, it does bring the increased chance of wet and stormy conditions across north-west Europe during the late autumn and early winter.

A forecast released by the Met Office this autumn stated that there were already "signals for increased rainfall and storminess in autumn here in the UK", especially into November and December.

The winter of 2015 and 2016, which coincided with a very strong El Niño, brought a succession of major storms delivering what experts at the time described as the most extreme flooding on record.

In addition to storminess, El Niño can also be associated with UK cold spells in the late winter - but the link is not a strong one and the past evidence is mixed.

The so-called Big Freeze of winter 2009/2010 was, at the time, the coldest in three decades - and this coincided with an El Niño.

However, 2006/2007 was also an El Niño winter and that was unseasonably warm.

As this unprecedented El Niño approaches its likely peak towards the end of 2026, scientists will continue to monitor its development - and its impact on weather around the world.