The El Niño effect, which can deal out both torrential rain and drought in different parts of the world, is underway in the tropical Pacific Ocean, with scientists suggesting it could be "substantial."
U.S. scientists with the National Oceanic and Atmospheric Administration announced the arrival of this year's event in March, but said at the time it appeared it would be a rather weak version.
Now, however, Australia's Bureau of Meteorology is predicting it could evolve to a "substantial" event later this year.
They are suggesting the possibility of a lasting event with severe weather implications for both sides of the Pacific Ocean.
The bureau has upgraded its monitoring status to El Niño level for the first time in 5 years, and warned the event was "likely to persist in the coming months."
El Niño events occur roughly every 4 or 5 years as prevailing trade winds in the Pacific weaken, allowing warmer water in the western ocean to move "backward" to the east, dragging rainfall with it.
The shift from usual patterns can bring major climatic impacts with drought in some countries in the Pacific region and heavy precipitation in others.
Past El Niños have brought wet winters to the U.S. Southwest while simultaneously afflicting northern Australia with drought.
The worst recent El Niño of recent years was in 1997-98.
Record temperatures around the world last summer had scientists expecting one to arrive then, but the phenomenon fizzled out.
While predictions of its strength in any year will always contain some element of uncertainty, "across the models as a whole we'd suggest this [year's] will be quite a substantial El Nino event," climate monitoring and prediction chief David Jones of the Australian bureau says.
Once an El Niño has started, scientists can use models to predict its development for the next 6 to 9 months with fairly good accuracy.
"As we move into summer we will get a much better idea of what the world may face with this particular El Niño," says Eric Guilyardi of the Department of Meteorology at England's University of Reading.
"The likelihood of El Niño is high but its eventual strength in the winter when it has its major impacts worldwide is still unknown," he says.
"We will know in the summer how strong it is going to be."
