The weather phenomenon known as El Niño is poised to return, a development that threatens to drive up prices for food and other staples, investors and analysts say.

Temperatures in the Pacific Ocean are rising, prompting US government forecasters to predict a more than 65% chance for an El Niño by the end of the year. El Niño is set in motion when winds in the equatorial Pacific slow down or reverse direction. That warms the water over a vast area and can upend weather patterns around the world. In 1997, a record-breaking El Niño caused heavy rainfall and mudslides in California and a water shortage in Australia.