The extraordinary rescue this week in Geographe Bay, Western Australia has been described as heroic. A 13-year-old boy swam four hours to shore in rough seas after his family was swept far from the beach. This boy’s bravery in raising the alarm is to be commended.

For the public, it’s useful to consider how the family found itself in this predicament. The boy’s mother told the ABC the weather conditions had rapidly changed. This is similar to other recent marine rescues.

According to the boy’s mother, conditions were calm when she and her three children set out on inflatable paddle boards and a kayak. But in a short time, strong winds and waves pushed them steadily out to sea, leaving them clinging to a board about 14 kilometres from shore.

How does weather change so quickly at sea – and why does it catch even careful people by surprise?

Read more: The ocean can look deceptively calm – until it isn’t. Here’s what ‘hazardous surf’ really means

Coastal weather is notoriously dynamic. Unlike conditions on land, which are shaped by friction from terrain, the atmosphere over the ocean can change rapidly as wind systems move unobstructed across large distances.

In southern WA, afternoon sea breezes are a key factor, such as the Fremantle Doctor. On warm days, air rises over land and draws cooler air in from the ocean. These sea breezes can strengthen rapidly in the late afternoon or early evening, sometimes........

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