The weather pattern known as La Niña could lead to a crisp, cold winter, followed by severe flooding in February, the Met Office has warned.
La Niña refers to the cooling of ocean surface temperatures coupled with winds and rainfall in the Pacific, but it can have knock-on effects on weather around the world.
The government is embarking on an awareness campaign, and says that two-thirds of people at risk of flooding were still unaware of the issue.
La Niña – Spanish for 'little girl' – often has the opposite impact on weather and global climate as the better-known El Niño, which is the warm phase of the so-called El Niño southern oscillation (ENSO).
Will Lang, the head of situational awareness at the Met Office said that La Niña leads to a higher chance of cold and dry conditions from November to January, but says that this may change in February.
Lang said: “The risk of unsettled weather increases as we head into 2023. This is another La Niña winter, as it was last winter, so it would not be unusual if the wettest and stormiest part of the season with the greatest flood risk again at that end of the season, in February, as it did last winter.”
“That pattern is broadly in line with what happens in the UK when we have La Niña in the tropical Pacific, so we get the knock-on effects that can tend to promote high pressure, which builds to the west of the UK in early winter,” he said.
Watch: What's the difference between El Niño and La Niña?
“That can in turn block the Atlantic rain-bearing systems reaching us in that first part of the winter. And then we tend to get a return to low pressures when that higher pressure fades, and we get all our wet conditions in late winter.”
The Met Office says that during La Niña strong trade winds blow warm water towards the west Pacific causing an upwelling of cool water from the ocean depths in the east Pacific.
This leads to variations in global weather – and the Met Office says it can influence the Atlantic jet stream and our weather here in the UK.
Professor Adam Scaife, head of long range prediction at the Met Office said in 2020, said: “La Niña has a profound effect on weather across the globe with us even seeing impacts that extend across the UK.
“In late autumn and early winter it historically promotes high pressure in the mid-Atlantic, which stops Atlantic weather systems from delivering mild air to the UK, and therefore can allow cold conditions to intensify.
“However, in late winter La Niña can drive a shift of the jet stream towards the poles increasing storminess and heavy rainfall, while bringing milder conditions”.
This year has seen the third cooling La Niña event in a row in the Pacific – known as a ‘triple dip’.
World Meteorological Organization (WMO) secretary-general Petteri Taalas said earlier this year: "It is exceptional to have three consecutive years with a La Niña event. Its cooling influence is temporarily slowing the rise in global temperatures – but it will not halt or reverse the long-term warming trend,"
La Niña is one of the three phases of the phenomenon known as the ENSO: El Niño or the warm phase; La Niña, the cool phase, and lastly the neutral phase.