Winter is not yet over in the Western Cape.
According to the South African Weather Service (Saws), while residents are looking forward to a fresh, spring season, the province is still experiencing cold, wet and windy weather from a series of cold fronts moving through the province.
The forecaster said conducive weather conditions colliding along with a spring tide event, resulted in a positive storm surge that wreaked havoc along the country's coastal areas at the weekend.
In a media statement, explaining the inclement weather, Saws unpacked the science behind the weather phenomena.
“Tides are long-period waves affected by the gravitational force of the sun, moon and earth's rotation. The timing and peak of tides are influenced by the wind and atmospheric pressure,” Saws said.
“Spring tide occurs every two weeks during the new and full moon and this causes high tides to be higher than usual.”
Saws added that spring tides brought in more water, up onto the coast, possibly resulting in coastal flooding and intense near-shore hazards like rip-currents.
It issued several weather alerts leading up to the weekend, including warnings of damaging waves along the Western Cape coastline.
Saws also issued an alert for a storm surge between Still Bay and Gqeberha.
Difference between storm surge and high waves
The forecaster explained that a storm surge is often widely confused with high waves.
“While they do frequently co-occur with waves, it should be noted that there is a distinction between the two phenomena.
“A storm surge is calculated as the difference between the expected or astronomical tide and the actual water level, including the effects of weather. Strong onshore winds and waves can further increase water levels at the coast.”
It added that when these waves occur during high tide or spring tide, they can exacerbate the impact on the coastline.
Therefore, storm surges can be severe and cause widespread impacts, but can also have little or no impacts when it coincides with a low tide.
Warning for damaging winds
Meanwhile, a Yellow Level 1 warning of damaging waves has been issued for areas between Cape Point and Struisbaai from Tuesday evening.
Saws stated that the first spring thunderstorms are possible for Gauteng, the North West, Free State and eastern Highveld.
Another cold front
“A weak cold front will approach the south-western Cape on Tuesday, resulting in showers and rain, while the atmosphere becomes conducive for isolated thunderstorm development from the afternoon over central SA, spreading eastwards reaching Gauteng and the eastern Highveld in the evening,” Saws said.