A spell of very cold and rainy
weather is expected to affect the Western, Northern and Eastern Cape later this
week, extending into the weekend.
This rainy spell will be heralded by the
arrival of a cold front over the south-western part of the Western Cape on
Thursday morning. Daytime temperatures are expected to drop significantly over
the southern half of the country, while a range of wintry weather can be
anticipated, including widespread significant rainfall and snowfalls over
mountainous terrain as well as marine gales and very rough seas over the
southern oceanic areas.
Upper-air
troughs, as well as closely related cut-off lows are a familiar feature of
weather over southern Africa and are associated with prolonged episodes of
rainfall, often of an extreme nature. It is noteworthy that the extreme
rainfall and flooding which affected KwaZulu-Natal (KZN) during April and May
2022 were associated with cut-off low weather systems on both occasions.
Firstly,
a well-developed upper-air trough will start nearing the Western and Northern
Cape from Thursday onwards, subsequently cutting off and establishing a cold
core, characteristic of cut-off upper-air systems.
Secondly, a particularly
strong southern Atlantic high-pressure system is expected to extend a ridge
eastward in the wake of the cold front, introducing pronounced and sustained
onshore flow along the southern coastline of Western Cape as well as the
Eastern Cape during the weekend. Moreover, the presence of coastal mountain
ranges (such as the Outeniqua and Swartberg) will enhance vertical motion of
air, thus enhancing the likelihood of heavy orographically-induced rainfall. It
is therefore this combination (or juxtaposition) of surface and upper-air
systems which is expected to raise the likelihood of significant, widespread
and heavy rainfall, especially over the coastal mountain regions, leading to
localised flooding.
Day-time
temperatures for this week are expected to drop significantly from Friday into
Saturday, where maximum temperatures may be below 10°C in places. Light
snowfall is possible over the south-western mountains of the Western Cape as
well as the southern high ground of Northern Cape on Friday afternoon into
Saturday.
The sea
state will also be affected with wave heights of 4.0 to 5.0 m between Alexander
Bay and Plettenberg Bay from Friday into Saturday. Strong to near gale force
south-easterly winds are expected north of Cape Point on Friday, while
spreading along the south coast on Saturday. These strong winds, accompanied
with significant wave heights, will result in very rough and choppy sea conditions.
Cloudy
and cold to very cold weather will dominate the Northern and Western Cape from
Friday onwards, spreading to include most of the Eastern Cape during the
weekend.
Widespread rain and showers will accompany this system, with the
likelihood of heavy rain and localised flooding being of particular concern for
the southern and south-eastern coastline and adjacent interior, as alluded to
earlier.
Given the expectation of an extended spell of cold, wet weather as
well as the possibility of snowfalls over mountainous parts of Western,
Northern and Eastern Cape, farmers of small stock are advised to move animals
to dry shelters at lower elevations. Moreover, only experienced, well-prepared
hikers and climbers should venture into the mountains and hiking trails of
Western and Eastern Cape this weekend. The risk of hypothermia in mountainous
terrain, especially if lost, injured or ill-prepared could prove to be
life-threatening.
