Oh No, It's La Niña

It seems like we've only just said goodbye to El Nino and already his evil twin sister La Niña has arrived on the scene.

El Nino dissipated in May, and hot on his heels La Niña became officially established in July and may persist at least into early 2011, according to Australia’s Bureau of Meteorology.

What the hell is this goddam thing?

La Niña conditions are typically caused by cooler than normal sea-surface temperatures in the central and eastern tropical Pacific Ocean. Temperatures along the equator during La Niña can fall as much as 7 degrees below normal in the eastern Pacific, as the easterly trade winds strengthen.

"The changeover from El Nino to La Niña is no small happening, usually taking several months to evolve. The global wind circulation doesn't just shift course overnight," explains Gail Martell of Martell Crop Projections.

"The summer of 1998 is the best analog for a very strong El Nino evolving into a La Niña. Extremely heavy rainfall drenched the Midwest in May and June, causing widespread flooding. Warm temperatures in 1998 mirrored the persistent heat that has dominated this summer in the Midwest. Yet a damaging drought never developed with a very slow transition to La Niña. September weather turned extremely hot and dry but it was too late to damage Midwest corn and soybeans," says Gail.

This years La Niña event appears to becoming established slightly later in the year than that of 1998, meaning that this winter could be warmer and drier than normal in the southern US, and it doesn't stop there.

"The odds favour an abnormally dry and warm period ahead for the southern Plains, intensifying drought in the SE US, wet weather for Australia and Indonesia and dry and cold weather in Argentina. It may be a dry fall and winter too in Central and NE China," says Allen Motew of QT Weather.

Dryness in Argentina over the next six months obviously has the potential to reduce production of wheat, corn and soybeans there. Meanwhile a warmer and drier pattern across the US southern Plains could also adversely affect the HRW wheat crop in states like Texas, Oklahoma and Kansas.

Dryness in Argentina may also spill over into southern Brazil and La Niña may also delay the arrival of rains in central Brazil, although when they do arrive they are frequently a deluge.

Central Brazil is currently hot and dry, as is normal for this time of year, with the seven day forecast calling for more of the same, which will take us through to the date when soybean planting can officially begin - September 15th.

We could be in for an interesting winter.