La Nina to Vanish by June, Returning Pacific to Normal

The cooling in the Pacific Ocean known as La Nina, which can influence Atlantic hurricanes and U.S. drought, is expected to keep fading and vanish by June, according to U.S. forecasters.

Observations and computer models agree on the weakening of the phenomenon, which also has been blamed for flooding in Australia, the U.S. Climate Prediction Center said today in a report on its website. Forecasters can’t predict whether it will remain weak or pick up strength after July, the agency said.

Neutral temperatures in the Pacific won’t do anything to diminish the number of Atlantic hurricanes this year, said William Gray, who makes seasonal hurricane forecasts at Colorado State University in Fort Collins.

“We’re forecasting a pretty active season for this year and we probably won’t change that much,” Gray said. “We can have very active seasons when it is neutral.”

The phenomenon peaked in early January and has diminished since, according to the Australian Bureau of Meteorology, which also tracks La Nina.

Global Impact

Rain linked to La Nina halted coal shipments and swamped cotton crops in Queensland earlier this year, after wet weather last year cut sugar output and downgraded east Australian wheat quality. La Nina has soaked rubber plantations in Southeast Asia, disrupted Indonesian tin output and brought dry conditions to corn and soybean areas in Argentina.

Photographer: Torsten Blackwood/AFP/Getty Images

Rain linked to La Nina halted coal shipments and swamped cotton crops in Queensland earlier this year, after wet weather last year cut sugar output and downgraded east Australian wheat quality. Close

Rain linked to La Nina halted coal shipments and swamped cotton crops in Queensland... Read More

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Photographer: Torsten Blackwood/AFP/Getty Images

Rain linked to La Nina halted coal shipments and swamped cotton crops in Queensland earlier this year, after wet weather last year cut sugar output and downgraded east Australian wheat quality.

“La Nina will continue to have global impacts even as the episode weakens through the Northern Hemisphere spring,” the U.S. center said. In the U.S., the effects from March through May may include below-normal rain across the South and Plains, and higher temperatures for the southern half of the country.

On average, La Nina occurs every three to five years and lasts nine to 12 months, with some persisting as long as two years.

The phenomenon has been blamed for enhancing hurricane development in the Atlantic by limiting wind shear there that can tear budding storms apart.

In December, Colorado State predicted 17 named storms, with winds of at least 39 miles per hour, would form in the Atlantic this year, nine of them becoming hurricanes with at least 74 mph winds. The university will update its forecast in April.

Hurricane Season

Last year, while La Nina gained strength, 19 named storms formed in the Atlantic, tying it for the third-most-active season on record with 1995 and 1887, according to the U.S. National Hurricane Center. A record 28 storms formed in 2005.

Hurricane season starts on June 1 and ends on Nov. 30.

Some forecast models predict the Pacific will return to neutral conditions, between a La Nina and the above-average warming known as El Nino.

Gray said getting an accurate read on what La Nina will do in three months’ time is difficult because forecasting confidence falls during March, April and May. Those three months are often called the “spring barrier” by U.S. forecasters.

“It is a tough barrier, you don’t know what is going to happen,” Gray said.

Meteorologist Allen Motew said he thinks La Nina won’t fade at all. While it may weaken, the Pacific will likely stay cool through next year, said Motew, a forecaster at QT Weather in Chicago.

“It may get near neutral around July but not quite make it and then go into a stronger La Nina in late summer and fall,” Motew said.

That would mean agricultural areas across the southern U.S. may face drought, he said.

The next Australian update on La Nina will be March 16, while the U.S. will revise its forecast in April.

To contact the reporter on this story: Brian K. Sullivan in Boston at Bsullivan10@bloomberg.net;

To contact the editor responsible for this story: Dan Stets at dstets@bloomberg.net.

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