Ricochet News

Significant drop in temperatures expected from Wednesday onwards

Aug 14, 2017
Significant drop in temperatures expected from Wednesday onwards

South Africans can expect a cold snap to affect most the country during the latter part of this week - from Wednesday onwards, the South African Weather Service said on Monday.

"Particularly cold daytime temperatures are expected to dominate the south-western parts on Wednesday, 16 August 2017, spreading to include the central and eastern parts on Thursday. Some places in the high-lying central and eastern interior are likely to experience daytime temperatures of the order of only 5 to 10 degrees Celsius for up to 3 consecutive days," described the weather office in a statement.

"Significant snowfall can also be expected over the southern and central Drakensberg. Snowfall could be heavy over the north-eastern parts of the Eastern Cape, possibly leading to the closure of the majority of mountain passes in the region as well as associated disruption of traffic flow.

"Rain and showers are expected over the south-western parts of the country on Tuesday and Wednesday.

"By Thursday, rainfall is expected to move eastwards, with the Eastern Cape and KwaZulu-Natal particularly well-favoured to receive widespread rainfall. These provinces may even experience heavy rainfall as well as localised flooding, especially along the coast and adjacent interior regions."

Along much of the southern coastline, periods of strong, gusty winds combined with moderate seas are expected. There is, however, a strong likelihood that gale force winds of a damaging nature as well as rough to very rough sea conditions may develop along the Wild Coast and KwaZulu-Natal on Thursday.

These extreme weather conditions are due to the development of an intense trough (an extension of a low pressure) in the upper portions of the atmosphere, which is expected to move over the country on Wednesday. Thereafter, the trough is likely to intensify further, becoming a so-called cut-off low pressure system on Thursday, 17 August 2017.

"By Friday, this weather system is expected to exit the country, when rainfall will be restricted to the eastern extremities of the country, heralding a return to dry, settled weather this weekend," the Weather Offcice said.

What is a cut-off low? A low pressure system, located in the upper portions of the atmosphere, which has separated away from the band of westerly winds in the upper-air and which dominates the midlatitudes of the northern and southern hemispheres respectively.

During a relatively short life span (typically a duration of a few days) a cut-off low generally drifts equatorward (northwards) and develops winds which are oriented clockwise around the core (or vortex) of the low. Cut-off lows are a
fairly common occurrence in the weather of South Africa, especially during winter.

A cut- off low is characterised by a cold core and is also referred to as an extra-tropical, mid-latitude cyclone. In contrast, tropical cyclones are an entirely different phenomenon, being characterised by a warm core and being restricted to tropical regions.

The South African Weather Service will continue to monitor further developments during this period and will issue subsequent updates as required. Furthermore, the general public are urged to regularly follow weather forecasts on television and radio. Updated information may also be accessed on www.weathersa.co.za  as well as via the South African Weather Service Twitter account @SAWeatherServic