Forecasters say the intertropical convergence zone is shifting south, signalling the return of the summer rainy season.
The first summer rains are expected soon, following a yellow level 1 warning for severe thunderstorms in parts of Limpopo, Mpumalanga and northern parts of Gauteng yesterday.
South African Weather Service senior forecaster Lehlohonolo Thobela said this weekend is expected to be partly cloudy and warm, with isolated showers and thunderstorms over the central and southern parts of the country.
Thobela said some areas in the north have a 60% chance of scattered showers and thunderstorms today, “On Sunday, partly cloudy and cool conditions are expected, with isolated showers and thundershowers possible, which may be scattered in places in the south,” he said.
It will be warm in the north of Gauteng, around Pretoria.
The intertropical convergence zone
Vox weather meteorologist Annette Botha said that the intertropical convergence zone (ITCZ) brings moist, unstable air from further south and, with the warmer weather expected during spring, causes thunderstorms to form over eastern South Africa.
Botha added that rainfall in Southern Africa was strongly influenced by the ITCZ.
The ITCZ changes position during the year, moving between the equator and the tropics of Cancer and Capricorn.
Seasonal rainfall patterns
Southern Africa normally receives the bulk of its annual rainfall from November through March as the ITCZ moves south.
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“The further south the zone moves, the more promising the rainy season. This does not mean there cannot be thunderstorms at all during spring.
“If the temperatures are high enough and there is just a little moisture in the air, thunderstorms will start to appear here and there, but usually Gauteng and the east’s first significant rain only arrives towards the end of October into November,” she said.
Botha said legend had it that the first summer rainfall in areas of Gauteng around Pretoria fell on 10 October, which was Paul Kruger’s birthday.
But there was some truth in it.
“Because it is usually in early October, close to Uncle Paul’s birthday, that the ITCZ begins to move south, bringing us summer rains,” she said.
Farmers ready for rain
TLU SA chair Bennie van Zyl said farmers were always 99.9 % ready for rain.
“But last year the rain arrived late and as a result, many farmers were only able to harvest late in the season.
“But it also left under-moisture, which can get the season started much quicker and with the first rainfall, it has a certain advantage.”
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