WHAT IS A SEA BREEZE?
Sea breezes are a geographically localised wind effect; a mesoscale front which may extend along a coastline but only move inland by a few kilometres. They are far more localised than prevailing winds and can cause an increase in wind speed in a local area beyond what has been forecast.
To understand a sea breeze, it is important that we first understand the effect of temperature on air pressure:
- Air pressure is the force exerted on a given area by the impacts of gas particles in constant motion.
- Cool air is greater in density than warm air, meaning that a warm air mass will expand and rise and a cool air mass will fall.
- As warm air rises in an area, this results in the area having low surface pressure.
- When cool air falls, this results in an increase in surface air pressure in that area.
- Air masses move from areas of high pressure to areas of low pressure.
- Convection is a form of heat transfer; warm air rises and cool air sinks. Convection is a natural way that heat moves from one area to another.
WHAT CAUSES A SEA BREEZE?
It takes longer for the sea to warm than it does for land to warm under the sun due to their comparative size. On a sunny day, solar radiation causes the temperature of land to rise creating a temperature gradient between land and water. As the temperature of the land increases, the air above it heats by convection. The warm, less dense air rises and causes a decrease in pressure over land. You can often spot this by the appearance of cumulus clouds.
Oversea, the air remains more dense and cool because the sea is cooler than land. This cool dense air is higher pressure than the air over land causing movement of the air mass (wind) from high pressure to low pressure. The strength of the sea breeze is proportional to the temperature difference between the land and the sea.
Its speed depends on whether it is assisted or hampered by the prevailing wind, and the strength of the thermal contrast between land and sea.
If a strong offshore wind is present that is greater than 8 knots, the sea breeze is not likely to develop.
When the wind is already blowing onshore, the combination of the original wind and the sea breeze means that the wind strength will increase dramatically. It can result in winds 1.5 or even 2 times the forecast strength.
It takes time for land to heat up and a temperature gradient to form. Sea breezes tend to start in the late morning/midday and can continue until sunset.
WELL KNOWN SEA BREEZE EXAMPLES
A well-known example of a sea breeze is the ‘Freemantle Doctor’ in Safety Bay, Australia. A Seabreeze so reliable that it made safety bay one of the number one winter training grounds for pro riders in recent years.
The mistral winds of the Med bless the Greek Islands every afternoon on hot summer days. The nearby mountains are so cold that they create a large temperature differential with the warm Mediterranean Sea. In the afternoons the warm rising air over the Med is replaced by a strong Landbreeze.
WHAT IS A LAND BREEZE?
As the sun sets, the land temperature begins cooling, and the wind dies down as the pressure gradients equalise. If the land cools off and the temperature falls below the temperature of the ocean, a land breeze may form on the same basis.
Sea breezes and land breezes are defined by where the wind comes from, and in both cases, the cooler air is the air that is moving.
HOW SEA BREEZES AFFECT KITESURFING?
It is important to recognise the conditions that may result in a sea breeze as the increase in wind speed may require a reduction in kite size. It takes time for the gradient conditions for a sea breeze to develop, but once it occurs the effects are quick and can result in a rapid and drastic increase in wind speed.
Sea breezes affect kitesurfing with positive and negative consequences. As they can so unpredictable kitesurfers can get caught out as their kites suddenly become too big. The wind can go from very low speeds, or even nothing, to blowing 20 – 30knots in a matter of minutes. Alternatively they may even need to self-rescue when the wind drops completely. It can be worth waiting for an hour or so to check how the wind is building so that you can know which size kite to take. Throughout your kitesurfing session, it is important to keep an eye on the formation of clouds and increasing wind speeds so that you can be prepared to downsize your kite as you recognise a sea breeze building.
SEA BREEZE TOP TIPS FOR KITESURFERS
- Watch for signs of a seabreeze such as low level cloud development over land on a clear, hot and sunny day. Consider sea breezes along with the rest of your kite spot assessment prior to kitesurfing.
- Be prepared to downsize your kite when a seabreeze comes in.
- Use caution, seabreezes can be unpredictable at times, light cloud cover may briefly dull a seabreeze but pick up again after the cloud has gone.
- Know how to self-rescue when the wind suddenly increases at the mid day or drops completely with the setting sun.