Niwa's principal climate scientist says that if an El Nino weather pattern develops this year, it could have a significant impact on east coast farmers.
El Nino - a natural pattern that occurs when the Pacific Ocean warms and trade winds ease - can bring with it extreme weather events. Climate experts in the United States are now officially on watch for it (the alert status up to now has been "not active").
Niwa's Brett Mullan says water temperatures in the western Pacific have been rising, "and the big change we've seen in the last month is this region of warmer water...has now extended almost all the way across the Pacific, and that's a fairly significant development."
Dr Mullan says there's a 50-50 chance of an El Nino but that could change quickly.
"A lot of farmers might be a little bit concerned if one develops," he says. "What happens with an El Nino is we tend to get more south-westerly winds and they tend to not only be a little bit cooler but drier as well."
Of more immediate concern to North Island farmers is a cyclone that could hit this weekend.