La Nina expected to dominate this rainy season

THIS rainy season will likely see the third consecutive year where South Africa’s weather is dominated by a La Nina system.

Three in a row is almost unheard of, say the weather experts, but the La Nina phenomenon is still largely unknown.

“We haven’t really been watching these La Nina much longer than about 25 to 30 years. And because they come once every five or seven years, there’s not that many for us to go back to and correlate with the rainfall,” says Professor Peter Johnston, a climate scientist at UCT.

La Nina is supposed to bring wet weather to South Africa.

It has to do with the cooling of sea surface temperature thousands of kilometres away in the Pacific Ocean.

El Niño is the opposite, when warming in the Pacific causes lower than average rainfall.

But sometimes La Nina doesn’t bring extra rainfall.

“Sixty times out of 100 it will affect the rainfall in the interior of South Africa and it will move the rainfall to the higher than normal category,” said Johnston.

This La Nina is expected not to be as strong as last year’s.

“We are expecting above normal rainfall, but it might not be as extreme as it was last year. And we are expecting above normal temperatures too,” said South African Weather Service (Saws) senior forecaster Dipuo Tawana.

The La Nina is expected to take hold later in the summer.

September, October and November are predicted to have lower than average rainfall.

What weather forecasters can’t predict is if there is going to be any flooding, such as that seen in KwaZulu-Natal in April. Johnston warned that the wet season had left the soil saturated and susceptible to possible flooding.

However, according to Saws, the predicted above-normal rainfall is not likely to benefit water reservoirs in areas of South Africa – like the Eastern Cape – that are experiencing ongoing droughts.

Why La Nina doesn’t bring extra rain to the Eastern Cape is not fully understood, said Johnston. But the hope is that it will do so this time and with it break the eight-year drought.

The summer ahead could also see heatwaves, says Tawana, with Limpopo and Mpumalanga experiencing temperatures in the 40s.

“From the beginning of September we are probably going to see isolated showers popping up here and there,” Tawana predicted.