La Nina triggered by a ‘pendulum effect’ which brings a rapid cool down in the eastern Pacific following months of El Nino warming.
It can last up to three years and comes with its own catalogue of weather effects which in the UK includes colder, wetter weather.
Britain could face a washout summer followed by another barrage of autumn storms and a bitterly cold winter as the atmosphere struggles to re-adjust.
El Nino has wrought havoc across the globe over the past year and although waning, experts warn now to brace for its La Nina counterpart.
Around the world La Nina is linked to heavier monsoons in Asia and persistent torrential rain in Australia which has previously sparked historic flooding.
Ocean warming in the Eastern Pacific intensified rapidly last year hitting a peak in December as temperatures rose 3C above average officially making it the strongest El Nino on record beating significant events in 1997/98 and 1982/83.
Although weakening, experts warn it won’t be long before the planet could start to experience the effects of La Nina.
According to satellite date from The National Oceanic and Atmospheric Administration (NOAA), the El Nino pattern is ending in dramatic fashion and could rapidly switch to La Nina.
La Ninas tend to generate colder than normal winters.
As La Nina strengthens the Atlantic becomes a spawning ground for violent hurricanes putting Britain on alert for another battering during the autumn.
The most immediate threat is on the summer with Britons waving farewell to any hopes of warm sunny weather if a La Nina pattern becomes established.
Like El Nino which means ‘the girl’, La Nina or ‘the boy’ causes a shift in global atmospheric circulation, atmospheric pressure and rainfall.
A strong event in 2010 coincided with the worst floods on record in Queensland, Australia, forcing more than 10,000 people from their homes.
La Nina is thought to have less of an impact in Europe and weather patterns can be unpredictable as records do not go far back enough to provide a definitive outcome.
Dr Nick Klingaman, climate scientist from the Department of Meteorology at the University of Reading said this El Nino has turned out to be the strongest on record.
Although not foregone conclusion, 90 per cent of El Nino events will trigger a subsequent La Nina, he added.
He said: “El Nino peaked in December with ocean temperatures in the Pacific hitting a 3C rise above average.
“Using this parameter, as opposed to the length of the peak, we can say that it ended up being the strongest on record.
“El Nino is weakening now and is forecast to do so over the rest of winter and spring decreasing the meteorological impacts.
“A La Nina event building up through the summer of 2016 before peaking in early winter is highly probably.”
He after El Nino peaks, there is a huge loss of heat from the Pacific into the atmosphere leading to a rapid cool down of ocean waters.
As systems try to rebalance, temperatures can dip lower than average triggering opposite or sometimes similar global effects to El Nino.
He said: “During El Nino, ocean temperatures are so warm and that is probably why 2015 was the warmest on record.
“The loss of heat from the ocean leads to systems over correcting themselves with temperatures dipping lower than normal and triggering a La Nina.
“About 90 per cent of El Ninos lead to La Nina and the effects are roughly opposite – flooding in Australia, South America and parts of Asia with milder effects in Europe.”
NOAA identifies this El Nino as having reached 2.3 on the Oceanic Nino Index (ONI) – an arbitrary index used to measure the strength of El Nino and La Nina events.
In 1982/83 it reached around 2.1 with the monster of 1997/98 hitting an unprecedented 2.4 on the scale.
Models show that by April a swing in the other direction will bring Pacific temperatures down to around 1.7C below average for the region.
On the ONI this equates to minus 1.5 similar to values seen after both of the previous major El Ninos.
In the months following the 1997/98 event Britain’s weather suffered major impacts now thought to have been driven by the resulting La Nina.
In January West Sussex was battered by a freak tornado while parts of the country were still shivering under thick snow by April.
A wet and miserable summer, which brought below-average temperatures during July and August in most places, was followed by a stormy run up to Christmas.
After the El Nino of 1983/84 the subsequent La Nina did not reach its maximum until the following January.
Consequently the summer was largely unaffected but the following winter saw Britain crippled by two major big freezes with heavy snowfall into April.
Climate models show La Nina will set in around March next year with Pacific Ocean temperatures showing a steady decline through to the summer.
David Parker, a climate research scientist at the Met Office, said: “La Nina has been linked to stronger monsoons in southern Asia and this can cause unsettled weather in northern Europe.”
El Nino starts when prevailing easterly ‘trade winds’ in the Pacific begin to weaken allowing warm water to build up around the coast of South America.
During a strong event the winds may reverse completely a with westerly currents becoming dominant for up to a year.
This stops ‘upwelling’ of deeper cooler water and the surface temperature rises unchecked with devastating consequences to marine life.