This year’s El Niño weather pattern could be the most powerful on record, federal forecasters said, while warning that the effects of the weather system are never certain.

“We’re predicting this El Niño could be among the strongest El Niños in the historical record,” said Mike Halpert, the deputy director of the Climate Prediction Center for the National Oceanic and Atmospheric Administration, in a teleconference with reporters. This year’s El Niño is already the second strongest for this time of year in more than 60 years of record-keeping, he said.

El Niño, which begins with warmer-than-usual water temperatures in the Eastern Pacific, can affect weather around the world — in the United States, it can bring heavy winter precipitation in California and across the South. El Niño events have also been linked to droughts in Australia and India, more numerous hurricanes in the Pacific Ocean (but fewer in the Atlantic), and a warmer planet over all.