La Nina expected to dominate this rainy season

SOON those first thunder clouds will be stacking on the horizon ready to send one of those famous Highveld thunderstorms to drench Joburg.

Thunder showers aren’t that unusual for the Highveld, but the invisible hand helping form them this year might be.

This rainy season will likely see the third consecutive year where our weather is dominated by a La Nina system. Three in a row is almost unheard of, say the weather experts, but then again, the La Nina 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 and correlate with the rainfall,” said Professor Peter Johnston, a climate scientist at UCT.

La Nina is supposed to bring wet weather to South Africa and it all has to do with the cooling of sea surface temperature thousands of kilometres away in the Pacific Ocean. El Nino is the opposite, the warming of 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,” explained 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 what was seen in Kwazulu-natal in April. Johnston warns that the previous wet season has 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 the 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, says 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. But that is all in the months ahead.

Here on the Highveld, that rain has yet to arrive. But the wait shouldn’t be long.

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