Storms and Gale-force Wind
Severe storms in the south-western Cape
Severe storms, linked to cold front and low-pressure systems, moving from west to east, occur mainly during the winter months in the south-western Cape. A frontal system or an inland cut-off low pressure system may have a surface wind gusting up to 100 kph or higher and may cause structural damage - roofs are blown off and trees uprooted. These storm systems are also intense rainfall producers and flooding (rivers bursting their banks and widespread urban and seepage flooding) can occur. Cold, including snow on the higher mountains, may also occur. Those living in low-cost housing or informal settlements are the most vulnerable.
Hailstorms may also occur when cumulonimbus clouds are present. Agriculture, gardens, buildings, vehicles, people, animals and birds may be affected.
Sea Surges and high waves may also cause some beach erosion and boat damage.
Gale-force winds may blow for a number of consecutive days during the summer months. Known as the “Cape Doctor”, these south-easterly or southerly winds can reach up to Gale-force in strength, usually blowing on clear, hot and sunny days and they are characterised by the “table cloth” over Table Mountain and the Hottentots-Holland mountains to the east of Cape Town. Caution needs to be taken, especially when walking in the Cape Town CBD and other areas where the wind may be unpredictable!
These windy conditions are also favourable for runaway fires that could easily become major blazes. The Fire Danger Index of a Red Warning for the Cape Metropole will most probably be in force during days with a Gale-force wind forecast. The general public are requested to apply fire-safe practices during these weather conditions - it is advisable not to make fires during this time, but especially not in open areas where the risk of a wildfire may be very high.
Precautionary measures to prevent wind damage
- Install straps or additional clips to your roof to secure it to the frame structure, in order to prevent roof damage.
- Trim trees and shrubs around your home.
- Determine how and where to secure your boat, should you own one.
- Maintain exterior walls.
- Protect windows and doors with covers or wind shutters.
- Reinforce double entry doors.
- Reinforce or replace damaged garage doors.
- Secure metal siding and metal roofs.
- Secure built-up and single-ply roofs.
- Brace gable-end roof framing.
- Ensure adequate insurance cover for possible storm damage.
- Motorists must watch out for fallen trees, branches and broken power lines along roadways.
- Exercise extreme caution in mountainous areas.
||Wind speed (km/hr)
||Wind speed (knots)
||Effects on land and sea
||Effects on land|
||< 1 kph
||Still, calm air, smoke will rise vertically. Water is mirror-like.
||Rising smoke drifts, wind vane is inactive. Small ripples appear on water surface.
||Leaves rustle, can feel wind on your face, wind vanes begin to move. Small wavelets develop, crests are glassy.
||Leaves and small twigs move, light weight flags extend. Large wavelets, crests start to break, some whitecaps.
||Small branches move, raises dust, leaves and paper. Small waves develop, becoming longer, whitecaps.
||Small trees sway. Whiotste crested wavelets (whitecaps) form, some spray.
||Large tree branches move, telephone wires begin to "whistle", umbrellas are difficult to keep under control. Larger waves form, whitecaps prevalent, spray.
||Moderate or strong Gale
||Large trees sway, becoming difficult to walk. Larger waves develop, white foam from breaking waves begins to be blown.
||Gale or Fresh Gale
||Twigs and small branches are broken from trees, walking is difficult. Moderately large waves with blown foam.
||Slight damage occurs to buildings, shingles are blown off of roofs. High waves (6 metres), rolling seas, dense foam, blowing spray reduces visibility.
||Whole Gale or Storm
||Trees are broken or uprooted, building or Storm damage is considerable. Large waves (6-9 metres), overhanging crests, sea becomes white with foam, heavy rolling and reduced visibility.
||Extensive widespread damage. Large waves (9-14 metres), white foam, with visibility further reduced.
||Extreme destruction, devastation. Large waves over 14 metres, air filled with foam, sea white with foam and driving spray and little visibility.
Advice on severe storms in the Cape
During the severe (winter) storms often experienced in the Cape, high wind speeds and heavy rain do not tell the whole story – localised or even wide-spread flooding and sea or storm surges along the coastline may also occur! By drafting your own Family Emergency Plan (refer to the Family Disaster Preparedness Guidelines) Link to relevant document in Resources and identifying all your risks, including those hazards affecting your own environment, you can make a positive contribution to preparedness.
Observe these common sense recommendations:
During a storm
- Remain indoors during the effects of a storm.
- Should you experience the passage of a storm's eye, you will be under violent storm winds and then all of a sudden lull or almost total calm. Do not go outside unless emergency repairs are absolutely necessary. The other side of the storm’s eye will approach and the winds will rise very rapidly to what they were, possibly from the opposite direction.
- The electricity, water, gas and telephone service may be interrupted. Stay calm and listen to your radio for the "All Clear." Do not leave your house to sight see.
After a storm (if you remained at your residence)
- When you go outside, do so during daylight hours. High water can drive snakes, animals and insects to high ground.
- Avoid downed wires, escaping gas, downed trees and structurally damaged buildings, puddles, etc.
- If you are tired, do not attempt to do anything but the most critical forms of repair. Remember, far more people are injured, and possibly killed, after a storm while trying to fix things.
- Notify relatives and interested friends that you are safe as it may be impossible for them to contact you.
- Check out all utility systems to be sure they are safe before turning them back on.
- If you are on city water, continue to use bottled water until authorized to use the water system. If you have your own well, continue to use bottled water until you can have your water tested.
- If power has been interrupted, check for the possibility of food spoilage.
- If power is out in your neighbourhood, be patient, the City’s Electricity Services / Eskom will be aware of it. However, if power comes on in your neighbourhood, but not in your residence, call your electricity service.
After a storm (if you evacuated your residence)
- Do not attempt to enter a disaster area unless it has been opened and you are a resident or worker in that area. If your area is under a curfew, be sure to honour its times.
- If your home has been damaged, enter with extreme caution. If you have gas connections do not light a match or smoke until you are sure there are no leaks.
- If your home has received damage contact your insurance company. If necessary, make arrangements to stay in alternative accommodation.