Water temperatures are rising in the central and eastern Pacific, Lerner said. As a result, warm, dry weather will occur from July through September, Lerner said today at an agricultural-investment conference in Chicago.

"The past few months, we've been in a warming trend," Lerner said. "The warm pocket in the Pacific has warmed another quarter-degree. This El Nino is coming on fast and it's coming on furious, and it will have an impact on world weather."

Parts of the southern U.S. from Texas to Florida will get less than the normal amount of rain in the next three months, Lerner said. Excessive rainfall and cooler temperatures will help plants in the U.S. Midwest, including Iowa and Illinois, he said.

"This is good for crops that were planted late," said Lerner, whose weather forecasting company is based in Kansas City. "We're going to dry out in the autumn. So people might be surprised by how well the crops do, despite being planted late."

Rainfall in India will decline during the critical monsoon season, which could affect crop development, Lerner said. India is the world's fifth-biggest grower of soybeans and third- largest rapeseed producer.