| ORLANDO, Florida
ORLANDO, Florida The U.S. government forecaster warned on Thursday that La Nina, the weather phenomenon blamed for searing drought in the southern United States and South America, may last longer than expected into the Northern Hemisphere spring.
In a trend that one analyst likened to the start of the Dust Bowl 80 years ago, the Climate Prediction Center said sea-temperature data suggests La Nina "will be of weak-to-moderate strength this winter, and will continue thereafter as a weak event until it likely dissipates sometime between March and May".
In its monthly report in December, it had said La Nina should dissipate "with the onset of the northern spring".
The prolonged phenomenon, although weaker than it was a year ago, threatens to roil commodity markets from corn to coffee as dry conditions in Argentina and Brazil whither crops while the southern United States -- a prime growing area for cotton and some wheat -- suffers through a once-a-century drought.
La Nina, which can last for several years, is the opposite number of the more infamous El Nino anomaly and is caused by an abnormal cooling of waters in the equatorial Pacific Ocean.
El Nino leads to warming of those waters. Both wreak havoc in weather patterns from South and North America to India and possibly even Africa.
"During December 2011 - February 2012, there is an increased chance of above-average temperatures across the south-central and southeastern U.S. below-average temperatures over the western and north-central U.S.," said the report from the CPC, part of the National Oceanic Atmospheric Administration (NOAA).
"Also, above-average precipitation is favored across the northern tier of states, excluding New England, and drier-than-average conditions are more likely across the southern tier of the U.S."
The effects of the current phenomenon are already being felt keenly in Latin America, where estimates for the 2011/12 corn crop from Argentina, the world's No. 2 supplier, have been slashed by as much as a fifth, while Brazil's soybean crop is also withering due to a prolonged dry spell.
Without persistent rains within the next two months, Argentina's soybean crop could also be at risk.
In the United States, an extended dry period could cause problems for farmers from the Carolinas to Kansas planning for sowing cotton in the spring, anlaysts said, particularly in top growing state Texas.
Ron Lawson, managing director of brokerage logicadvisors.com in Sonoma, California, said La Nina is worrying because conditions in parts of Texas are worse this year and could easily spread into the U.S. grain belt.
"The conditions that exist today are identical to what existed before the Dust Bowl," he said.
The Dust Bowl hit the United States and Canada from 1930 to around 1940, giving birth to huge dust storms that whipped farms in the U.S. Midwest.
Hector Galvan, senior market strategist for RJO Futures in Chicago, added that "if La Nina does create dry conditions ... we would see the domestic grain markets move significantly in the spring".
Although recent storms have helped restore moisture in Kansas, the severe Southern drought in Oklahoma and Texas has already drained the soil there, Sterling Smith, senior analyst at Country Hedging Inc said.
"If that were to happen and the dry pattern that usually accompanies La Nina were to occur, then it adds to an already challenging situation, particularly for Texas because they're starting the year in a moisture deficit," said Gary Adams, chief economist of industry group National Cotton Council.
He made the comment at the annual Beltwide Cotton conference in Orlando, Florida.
In leading palm grower/exporter Malaysia, severe monsoon rains from La Nina could disrupt harvesting and boost palm oil prices.
The same rains could hit top robusta coffee producer Vietnam and leading rice importer the Philippines.
Rains in the December to March period are also posing a threat to the coffee crop in Colombia, the world's top source of high quality beans.
La Nina lasting until the Northern Hemisphere spring would also bring it to the cusp of the start of the annual Atlantic hurricane season on June 1.
In the last two years when La Nina was present, more storms formed in the Atlantic Ocean, but most veered away from the U.S. mainland, with the exception of Hurricane Irene and the severe damage it caused in states from New Jersey to Vermont.
"There are more markets that would be affected by dry La Nina conditions, but I would say that the grains are where many would concentrate their fears," said Galvan.
(Reporting By Rene Pastor; Editing by David Gregorio)