Cold, wet, windy weather here for the week

A well-developed, fast-moving cold front arrives over the Western Cape Wednesday, introducing very cold, rainy weather to all three of the Cape provinces. In addition, strong, gusty westerly winds over the interior are expected to accompany the passage of the cold front. Given the dramatic drop in temperature, combined with persistent wet and windy conditions in the days ahead, small stock farmers are strongly encouraged to take action to prevent stock losses due to exposure.

The arrival of the cold frontal system Wednesday will be the first in a succession of such systems, expected to pass through the Cape provinces in the week ahead, on an almost daily basis. Cold, windy conditions with occasional showers will therefore be a persistent feature of the weather over the southern half of the country, continuing until well after the long weekend.

The latest output from Numeric Weather Prediction (NWP) models, in particular the Unified Model (UM) (refer Figure 1 below) suggest that heavy rainfall may occur over parts of Western Cape tomorrow Wednesday 14 June, persisting on Thursday 15 June. Typically, the presence of higher topography and especially mountainous areas tends to markedly enhance local rainfall through orographic uplift. The western, or windward, side of hills and mountains of the Western and Northern Cape can therefore expect to receive upwards of 100 mm of rainfall on Wednesday, with further significant rainfall of the order of 50mm or more, persisting on Thursday. This NWP guidance has prompted SAWS to issue a Level 6 Orange warning for disruptive rainfall, expected to affect particularly the Cape Town CBD and Metropole as well as the Winelands area (see additional details below).

Strong, gusty winds (possibly gusting beyond gale-force) are anticipated over much of the interior of Western Cape and Eastern Cape tomorrow and Thursday. High-sided vehicles travelling along major roads and highways could be at risk of being severely buffeted by crosswinds. Drivers of such vehicles are encouraged to reduce speed and to exercise due caution in this regard.

Figure 1: Numerically modelled 24-hour rainfall in mm, based on the Unified Model (UM), valid for Wednesday, 14 June and Thursday, 15 June 2023 (at top left and top right respectively). Source: Meteologix.com

Strong to gale force winds are expected to occur along the Western Cape coast between Saldanha Bay and Plettenberg Bay on Wednesday and Thursday, combined with very rough sea conditions of 4,5 to 5,0m, which will lead to difficulty in navigation at sea and may cause problems for small marine vessels.

Impact-Based weather warnings have been issued by the South African Weather Service (SAWS) for two areas in the Western Cape.

A Yellow Level 2 Warning for disruptive rain leading to localised flooding of roads and settlements can be expected over the southern West coast, south-eastern Cape Winelands and western Overberg districts on Wednesday and Thursday (14-15/06/2023).

Impacts may include difficult driving conditions and minor motor vehicle accidents due to slippery roads.

An Orange Level 6 Warning for disruptive rain leading to major disruption of traffic flow can be expected over the City of Cape Town and most parts of Cape Winelands on Wednesday and Thursday (14-15/06/2023).

Impacts may include flooding of roads and settlements and damage to property and infrastructure.

Furthermore, members of the public are encouraged to regularly follow weather forecasts on television, radio as well as social media platforms. Updated information in this regard will regularly be available at www.weathersa.co.za as well as via the SA Weather Service Twitter account @SAWeatherServic