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The current El Nino weather phenomenon is expected to peak between October and January and could turn into one of the strongest on record, experts from the World Meteorological Organization have warned.
Climate models and experts suggest surface waters in the east-central Pacific Ocean are likely to be more than 2 degrees hotter than average, potentially making this El Nino one of the strongest ever.
Typically, the warm air above the eastern Pacific is causing increased precipitation over the west coast of South America and dry conditions over the Australia/Indonesia archipelago and the Southeast Asia region, said Maxx Dilley, director of the WMO's Climate Prediction and Adaptation Branch.
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Pictured is a comparison of sea surface height in the Pacific as measured at the end of July in 1997 and 2015. Comparing the two years, 1997 seems slightly less intense. But trade winds collapsed and the eastern Pacific warmed dramatically from August through November 1997, setting the stage for a turbulent winter
El Niño is caused by a shift in the distribution of warm water in the Pacific Ocean around the equator.
Usually the wind blows strongly from east to west, due to the rotation of the Earth, causing water to pile up in the western part of the Pacific.
This pulls up colder water from the deep ocean in the eastern Pacific.
However, in an El Niño, the winds pushing the water get weaker and cause the warmer water to shift back towards the east.
This causes the eastern Pacific to get warmer.
But as the ocean temperature is linked to the wind currents, this causes the winds to grow weaker still and so the ocean grows warmer, meaning the El Niño grows.
This change in air and ocean currents around the equator can have a major impact on the weather patterns around the globe by creating pressure anomalies in the atmosphere.
Dilley said: 'we have a well-established El Nino event under way,' and farmers, rescue officials and reservoir operators would be among officials bracing for its rise.
El Nino can also bring higher rainfall and sometimes flooding to the Horn of Africa, but causes drier conditions in southern Africa, Dilley said.
'A mature and strong El Niño is now present in the tropical Pacific Ocean,' the WMO said.
Climate scientists are better prepared than ever with prediction models and data on El Nino patterns, but the impact of this El Nino in the northern hemisphere is hard to forecast because there is also an Arctic warming effect at work on the Atlantic jetstream current.
'The truth is we don't know what will happen. Will the two patterns reinforce each other? Will they cancel each other? Are they going to act in sequence? Are they going to be regional? We really don't know,' said David Carlson, the director of the World Climate Research Programme.
This El Nino could also be followed abruptly by a cooling La Nina, which, along with the advance of global warming, was adding to the uncertainty, Carlson said.
'I think we all think that there's some climate warming signals starting to show up in the El Nino record,' he said.
But he added that it is still unclear how global warming is affected the frequency or magnitude of El Nino events.
Scientists said earlier this summer conditions in the Pacific are now as intense as they were in the summer of 1997, when a massive El Niño was brewing.
While this could be good news for drought-stricken areas such as California, researchers warn it may also lead to torrential and hazardous downpours elsewhere.
El Nino events tend to warm the Earth's atmosphere by supressing the upwelling of cold water from the ocean that can absorb excess heat.
But as well as bringing relief, El Niño can have devastating consequences for agriculture.
It can trigger heavy rains and floods in South America and scorching weather in Asia and as far away as east Africa.
Pattern of sea surface temperature deviation from average (°C) associated with a unit value of the C index (top) and the E index (bottom), based on Takahashi et al., 2011. The Niño 3.4 and 1+2 regions are indicated as dashed boxes. Most El Niño events can be described as a combination of these two patterns. Image from Ken Takahashi.
'We have not seen a signal like this in the tropical Pacific since 1997,' said Bill Patzert, a climatologist at Nasa.
'It's no sure bet that we will have a strong El Niño, but the signal is getting stronger. What happens in August through October should make or break this event.'
The pulses of warmer water moving across the ocean are Kelvin waves.
Shown here are snapshots of average sea surface height changes at four different moments since March 2015. Shades of red indicate where the ocean stood above normal sea level because warmer water expands to fill more volume. Shades of blue show where sea level and temperatures were lower than average
Sea level is naturally higher in the western Pacific; in fact, it is roughly 40 to 50cm (15-20 inches) higher near Indonesia than off of Ecuador.
Much of this difference is due to tropical trade winds, which predominantly blow from east to west across the Pacific Ocean, piling up the water near Asia and Oceania.
When those trade winds ease and bursts of wind come out of the west, warm water from the western Pacific sloshes east in vast and deep waves and evens out sea level a bit.
As the warm water piles up in the east, it suppresses the natural upwelling that usually keeps waters cooler along the Pacific coasts of the Americas.
The seas and skies have been doing just that in 2015.
According to observations compiled by the National Oceanic and Atmospheric Administration (NOAA), at least three sizable west wind bursts have occurred in the Pacific since March.
Each came shortly before a Kelvin wave rolled across the basin.
Those waves have raised water temperatures in the central and eastern Pacific by as much as 1.6 degrees Celsius (2.9° Fahrenheit) above normal, making for a 'strong' El Niño.
The warmers waters off the west coast of the Americas have led to warmer and more humid weather ashore, as well as soaking bursts of rain.
At the same time, Indonesia and other parts of the western Pacific have been unusually dry.
'Sea surface temperatures in the eastern Pacific have been waxing and waning,' Patzert said. 'Right now they are waxing.'
But will sea surface conditions and winds amplify the warming signal and produce an El Niño to rival 1997–98?
'This El Niño is getting billed as the 'great wet hope.' Many people in the American West are looking to El Niño to save them from drought,' Patzert noted.
But he cautioned that '1997 was mayhem,' and drenching rains on a parched landscape are just as hazardous as a drought.
El Niño typically peaks between December and April, so only time will tell if this event will be potent.
The US National Oceanic and Atmosopheric Administration has detected warmer than average water surface temperatures around the equator of the Pacific Ocean (shown above) which indicates the arrival of El Niño
The National Weather Service's Climate Prediction Center said there is a 90 per cent chance that El Nino would continue through this winter
Many of the models and observations suggest it will be, but other factors such as the 'warm blob' in the North Pacific and the apparent shift in the Pacific Decadal Oscillation could affect further development.
'With hopes for drought relief running so high in California, it can't be stressed enough that El Niño shifts the odds but doesn't guarantee the roll of the meteorological dice in any particular winter,' wrote meteorologist and blogger Bob Henson.
Scientists from Nasa's Goddard Space Flight Center and other institutions recently found that California has accumulated a 'rain debt' of about 50 centimeters (20 inches) between 2012 and 2015. That is the amount that would normally fall in an entire year in the state.
And even if the rains come, they do not necessarily solve drought problems in areas that rely on snow pack for summer supplies.
'It took a long time to get into this drought,' Patzert added, 'and it is more of a systemic problem than just a lack of rain or snowfall.'
Earlier this year, the National Weather Service's Climate Prediction Center said there is a 90 per cent chance that El Nino would continue through this winter.
It added that it could help relief the drought in California and that there is an 80 per cent likelihood it would last into the Northern Hemisphere's early spring.
The forecast could be good news for a drought-stricken California. In previous strong El Niño events, California has seen a 150 per cent to 200 per cent increase in rainfall