Ever wondered how a storm can push the sea inland? Here’s what you need to know about storm surges, high tides and King Tides.
If you live near the coast, you may hear weather officials talk about storm surges, high tides and King Tides. These terms can sound complicated, but they describe different things.
Understanding the difference is important because when they occur together, they can increase the risk of coastal flooding.
A storm surge is a temporary rise in sea level caused by a storm.
When a strong storm moves near the coast, its powerful winds can push large amounts of seawater towards the shoreline. The storm’s low atmospheric pressure can also cause the sea level to rise.
Instead of the sea staying around its normal level, the water is pushed towards land.
If the surge is strong enough, seawater can move beyond the beach and into roads, homes, businesses and other low-lying areas.
A high tide is the normal rise of the sea to its highest level during the daily tidal cycle.
Tides happen naturally because of the gravitational pull of the Moon and, to a lesser extent, the Sun.
Most coastal areas experience rising and falling tides throughout the day. When the water reaches its highest point, that is high tide.
On its own, high tide is not unusual or dangerous. The problem comes when a storm surge reaches the coast at the same time as high tide.
The sea is already higher than normal, so the storm has less distance to push the water before it reaches coastal areas.
On the other end a King Tide is an exceptionally high tide; it is basically still a natural tidal event and is not caused by a storm.
King Tides happen when the positions of the Earth, Moon and Sun create conditions that produce higher-than-usual tides.
King Tides can cause some minor coastal flooding in vulnerable areas even without a storm. But if a storm surge arrives at the same time, the two can combine and produce much more serious flooding.
A storm surge is when a storm pushes the sea towards the land and when that happens alongside high tides and large waves, the water can move much further inland and cause serious flooding.
Strong winds can push seawater towards the coastline, while the low pressure associated with a storm can cause the sea level to rise.
When large waves arrive with the surge, they can push water further inland and cause flooding.
The shape of the coastline also matters. Low-lying areas are generally more exposed because water can move inland more easily.
Low-lying coastal communities face the greatest risk, particularly areas close to beaches, estuaries, harbours and other exposed parts of the coastline.
Coastal roads and infrastructure can also be affected when seawater moves inland.
Keep an eye on South African Weather Service (SAWS) warnings for updates and also follow updates from local disaster-management authorities.
Stay away from shoreline and move to higher ground. Avoid beaches, estuaries and flooded roads, and never drive through moving water.
Do not go to the coast to watch the storm as large waves can arrive unexpectedly.
The safest option is simple: follow SAWS warnings, stay away from the shoreline and move to higher ground if flooding threatens.
