There is a greater than 70% chance that an El Niño event will kick off in the equatorial tropical Pacific Ocean during the next four months, the Australian Bureau of Meteorology (BOM) said in a long-range forecast released on Tuesday.

El Niño events are characterized by above average sea surface temperatures in a portion of the tropical Pacific Ocean, and can bring major changes to global weather patterns from the Western U.S. to sub-Saharan Africa.

The Australian forecast comes as scientists studying surface and sub-surface conditions across the tropical Pacific have picked up signs of a potentially rapid transition to what could wind up being a more intense El Niño event than average.

"... Surface and sub-surface ocean temperatures have warmed considerably in recent weeks, consistent with a state of rapid transition," the BOM statement said. "International climate models surveyed by the Bureau indicate continued warming of the central Pacific Ocean in coming months. Most models predict sea surface temperatures will reach El Niño thresholds during the coming winter season," the Bureau stated, referring to the Southern Hemisphere winter period, or the summer in the Northern Hemisphere.

In Australia, El Niño events often lead to below average rainfall during the second half of the year, sometimes resulting in widespread droughts. In the U.S., El Niño events tend to have their biggest influence on winter weather, bringing wetter conditions to the West and Southern tier of the country. This would be potentially good news to drought-stricken areas like California and Texas, although there is no guarantee that an El Niño would break the drought conditions.

While the BOM said that "It is too early to determine the strength of this potential El Niño," other scientists have told Mashable that recent developments point toward the upcoming event being a moderate to strong one, if it does indeed take place. The sub-surface ocean conditions in the tropical Pacific resemble conditions in April of 1997, when a record El Niño was just beginning to develop. Ocean buoys have picked up on an area of unusually mild ocean waters that are moving eastward, past the International Dateline, in a movement known as a downwelling Kelvin Wave. Depending on a variety of factors at the surface and sub-surface, these mild waters may reach the surface of the eastern equatorial Pacific during the next few months.

Image: Australian Bureau of Meteorology

"Since January, a large volume of warmer-than-average water ... has progressed from the western Pacific sub-surface to the central Pacific sub-surface and warmed, eroding the cooler waters in the east," the BOM stated.

"Water below the surface in the central Pacific is now more than 7.2 degrees Fahrenheit warmer than average in some places." As Mashable reported in March, the Kelvin Wave itself may rank as one of the strongest in the observational record.

Some scientists think this event may even rival the record El Niño event of 1997-1998. If that does happen, then 2015 would almost be guaranteed to set a record for the warmest year on Earth, depending on the timing of the El Niño conditions. El Niño events tend to work in tandem with manmade global warming, both adding heat to the oceans and atmosphere, raising the odds of setting a new temperature record. However, forecasting the intensity of these events months in advance is fraught with uncertainty

Scientists at the BOM and at the National Oceanic and Atmospheric Administration (NOAA) in the U.S. had already put the world on notice that an El Niño event might be taking shape, but the Australian projection is the most confident of any statements issued to date. Making it even more noteworthy is the fact that unlike NOAA, which requires tropical Pacific Ocean waters to be at least 0.9 degrees Fahrenheit above average for at least three straight months before declaring that an El Niño is underway, the Australians use a tougher standard. The BOM requires three consecutive months with water temperatures of at least 1.44 degrees Fahrenheit above average before they will declare an El Niño event in progress.

This means that if the Australians are saying there is a 70% chance of an El Niño developing by winter, it is likely that the next NOAA El Niño update, which will be released on Thursday, may also raise the odds in favor of such an event.

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