Surfer’s guide to science of Wind

Introduction to Science of Wind & Waves

The sun is the source of all energy. The laws of physics dictate that energy cannot be lost or destroyed – only transferred or transformed. The sun’s energy is transferred into heat, which causes differences in air temperature and pressure, leading to the movement of air—wind. Wind is kinetic energy that transfers its energy to the ocean’s surface, generating capillary waves. These small ripples can grow into larger, set waves as they travel long distances.

In summary, the Sun’s heat drives the formation of wind. If the wind blows long enough and with sufficient strength, it generates ocean waves. Ocean waves are similar to other types of waves in physics, but they are unique in that they travel long distances across the ocean and release their energy near the shoreline. It is the energy of these breaking waves that surfers ride.

Introduction to effect of Wind on Waves

The quality of the wave created for surfing is dependent on the size of the fetch and the duration the wind was blowing for. A bigger ocean surface area with wind blowing for longer makes better quality waves. Also, the longer the distance the waves travel before arriving at the shoreline, the more the wave quality improves.

If the source of the storm is too close then the surf will be wind swell and not good for surfing. Many surfing destinations in the world are too close to the storms that created the waves to get clean long range ground swells, and are affected by the winds from these storms.

Bali and other Indonesian islands are far away from the source of the storms (which are in the Southern Indian Ocean at latitudes typically between 40 and 50 degrees south). However, the surf will be very much affected by local winds, which is why you will frequently hear surfers talking about onshore and offshore winds. In summary, offshore winds are good for surfing and onshore winds are bad. Side shore can be as bad or worse as onshore, while cross offshore can be as good as offshore.

Convection currents

When there is stable weather present, think of California or France in summer, then the local winds at the beach are determined by convection currents. In the night time the land will cool off, while the sea water temperature does not change. When the land is cooler than the water the wind will blow offshore. Early or mid-morning, when the sun warms up the land to the same temperature as the sea, the wind will stop. As the sun gets stronger and the land warmer, the wind will turn onshore and get strongest in the afternoon when maximum land temperature is reached. Before sunset the land will cool down and the winds will get lighter. The same cycle is repeated daily, giving the very best surfing conditions in the early morning. Before sunset the wind will usually drop down and could turn offshore.

Trade winds

Trade winds are a consistent feature of tropical regions under stable weather conditions, driven by the Earth’s rotation and pressure systems. During local storms or weather disturbances, wind patterns become more variable and less predictable. Additionally, wind forecasts in tropical regions can be less reliable compared to temperate zones because tropical weather systems tend to be more dynamic and rapidly changing, influenced by the complex interactions of solar heating, ocean currents, and atmospheric conditions.

Now that you understand wind and its effect on surfing, you are ready to read about Swell Period and how to read a swell forecast. Note when looking at wind forecast information that tropical regions can be less reliable compared to temperate zones because tropical weather systems tend to be more dynamic and rapidly changing. In Bali the mountains, ocean and sun combine to make wind forecasts unreliable, particularly in the rainy season.

Onshore winds

Onshore winds are particularly unfavourable for surfing because they tend to chop up the waves and make them difficult to surf. When the wind blows from the ocean toward the shore, it disrupts the formation of clean, well-shaped waves, and can make the conditions unrideable. Light onshore winds can have little effect, but in general, onshore conditions diminish the quality of the surf, making the waves break sooner than they would otherwise.

Side shore winds have basically the same effect on surfing conditions unless there are local factors like piers or headlands that protect the surf break. For example, Baby Padang and Balangan have headlands, so they have some protection from side winds.

Offshore winds

Offshore winds are much more desirable for surfing because they help to shape and clean up the waves. When the wind blows from the land toward the ocean, it causes the waves to become more well-formed, smooth, and easier to ride. Offshore winds hold the wave face, making the waves break cleaner and more predictably. Light offshore winds can enhance wave quality without causing problems, but strong offshore winds might create other challenges such as spray in your face. Depending on the distance from shore, a strong offshore wind can chop up the waves in a way very similar to an onshore wind. Overall, offshore conditions significantly improve the quality of the surf by allowing the waves to break more predictably, and for longer. It also helps to form barrels.

The distance a break sits from the shoreline matters here, because that distance gives the offshore wind a fetch of its own. A break close to the beach has almost no fetch for the offshore wind, so even a strong land breeze simply grooms the wave face. The Airport reefs are the opposite case: they break a long way out to sea, so a strong offshore wind has a long stretch of water to blow across before it reaches them. With enough fetch the offshore wind builds its own chop and ruffles the wave face, so a wind that cleans up a beachfront break can actually make the Airport reefs unrideable. As a rule, the further out a break is, the lighter the offshore wind needs to be to stay clean.

Cross-offshore is similar to offshore but the distance from the shoreline is more acute, and it then depends on the absolute direction of wind and strength, along with local conditions. Offshore or cross-offshore – go surfing!

Conclusion

Wind not only makes the waves, but also affects how they will break at your local spot. Understanding winds, and how they affect the wave quality, is crucial along with swell forecasting to plan surf sessions.

If you want to know more about the science of waves then read why Bali is the world’s most consistent surf destination.

If you want to surf Bali with a leading surfing company who understands winds and the science of surfing, then please get in contact or book a surf session online.

Included with a stay at Padang Padang Surf Camp is onsite surf coaching and tutorials for beginner, intermediate and advanced surfers.