It may not be the kind of news growers like to hear, but rain during the period when California farmers harvest cotton and tree nuts this year is more likely than not, as the Pacific Ocean transitions into a short-lived El Niño pattern.

Forecasters are growing confident in the likelihood that El Niño will impact weather patterns this winter across California. Just how much and to what extent is uncertain. El Niño does not always portend wetter-than-average years.

WeatherBell, a private weather forecasting service, and the National Weather Service (NWS), suggest the likelihood of an El Niño will be 70 percent by September and closer to 80 percent by November.

What does it mean for California agriculture?

According to WeatherBell Chief Meteorologist Joe D’Aleo, the chances of an early rainy season in central and southern California are more likely than not, with a good chance that the weak to moderate El Niño event will peak by late in the calendar year. D’Aleo expects the rainy season to stretch into early 2015.

D’Aleo expects the short-lived El Niño could expand to bring above-normal precipitation to all of California by the January-February period before ocean temperatures cool below the El Niño threshold and West Coast weather patterns return to near normal.

The potential September start to this year’s rainy season could impact California’s cotton harvest plus tree nuts and rice, though D’Aleo says northern California could remain in a drought pattern until later in the year, thus possibly sparing California’s rice crop from rain.

“We’ll likely see our first Pacific El Niño system by October,” he said.