Severe Weather Alerts issued by the Cape Town Weather Office

Hazard: Damaging Winds

Alert Level: Warning

Valid from (SAST): 29/10/18, 01h00 – Valid to (SAST): 30/10/18, 11h00

WARNING: Gale force W/SW winds of 65-75km/h is expected along the coast between Hermanus and Plettenberg Bay tonight (Monday), into tomorrow (Tuesday) morning.

ADVISORY: Strong interior winds (50-65km/h) are expected over the Matzikama Municipality, Breede River Valley, Central and Little Karoo today (Monday), into early tomorrow (Tuesday) morning.

Description: Strong damaging winds
Strong damaging winds often occur along coastal regions, but also often occur during thunderstorm activity. These winds are sudden and can cause much damage.

Precautions:  Strong damaging winds
Stay indoors where possible away from the windows that open towards the severe winds. Be aware of the following: – sudden cross winds if traveling especially between buildings, fallen trees or power lines and flying debris.
Small boats must stay away from the open sea and seek the shelter of a harbour, river estuary or protected bay.
Parked aircraft should be pointed into the direction of the wind and secured.  Listen to the radio or TV for warnings and obey the instructions from the Disaster Management Officers.

Description: Storm surges / High Seas

Generally heavy seas or damaging waves are a result of strong winds blowing over a large area called a fetch combined with low pressure systems. Long period swells are often very dangerous to tankers as they may literally snap them in half. Dangerous waves or surges may also be caused by storm surges and tsunami’s resulting in widespread coastal damage and loss of life.

In oceanography, a sea state is the general condition of the free surface on a large body of water—with respect to wind waves and swell—at a certain location and moment. A sea state is characterized by statistics, including the wave height, period, and power spectrum. The sea state varies with time, as the wind conditions or swell conditions change.

Precautions: Storm surges / High Seas

Ships should “idle” into the swell and wind so that the bow of the ship always faces the oncoming swell. If in a small sailing vessel reduce the sail area and steer into the oncoming swell. If along the shore-line stay well back from the highest high water mark as Secure all hatches, doors, windows and ports. Secure all loose items in the interior.

Pump the bilge’s dry and keep pumping them dry at regular intervals. Stow away all loose gear and lash down any large items that cannot be stowed. Break out your life preservers and inform your crew that everyone will be putting them on well in advance of their necessity.

Break out emergency gear like flares and first aid kit, sea anchor, safety harnesses, etc.  Check your position and update your course as plotted on your chart. Prepare alternative routes to more protected areas. If you think you will be in for relatively long haul prepare some hot soup, coffee or stew freak waves may run up beyond the normal high water mark.

If the sea recedes exposing rock and sea bed normally not exposed immediately seek higher ground at least 50m above your current position. Do not try swimming or fishing or other marine recreation during these events. Only extremely experienced surfers will temp their fate under these conditions.

Listen to the radio or TV for warnings and obey the instructions from Disaster Management Officers.