Simply look at a flag and you can reckon one of the most important surf factors. If it’s pointed toward the Ocean or hanging slack, quicken your pace towards the sea. It has an enormous impact on our daily surf conditions, and in fact it is mostly responsible surf’s existence. Moving air. We call it wind. The creator and sometimes destroyer of our waves.

The atmosphere from space. Image: NASA

The atmosphere from space.     Image: NASA

The Earth’s atmosphere is roughly 60 miles of gases that surround the planet. If Earth were the size of a classroom globe, the atmosphere would only amount to a couple layers of paint. Composed mostly of nitrogen and oxygen, the atmosphere is held in place by Earth’s gravity. We live and surf in the very base known as the troposphere. 

Atmospheric pressure is the measure of how much air is pressing down on a given region on Earth’s surface. The movement of air from areas of high pressure to areas of low pressure is the primary cause of Earth’s surface winds. The Sun heats the Earth unevenly, so the atmosphere always contains different temperature gradients. As air molecules lose energy, they cool down, becoming more dense and sink through the atmosphere. As air molecules gain energy, they heat up, becoming less dense and rise in the atmosphere. This flow is called convection and its happening all around all the time.

Strong low pressure with surrounding areas of high pressure over the North Pacific.  Image: NWS

Strong low pressure surrounded by areas of high pressure over the North Pacific.     Image: NWS

Atmospheric convection creates the high and low pressure that we associate with our weather. As the warm air rises, the pressure on the surface drops. When cool air descends, the pressure on the surface increases. High pressure generally brings clear skies, light wind and stable weather. Low pressure generates precipitation, strong winds and unstable weather.

When the pressure drops, air rushes in and wind speed increases as the atmosphere attempts to find equilibrium. The rotation of the Earth causes the wind to also move in a circular pattern. Counter clockwise in the Northern and clockwise in the Southern Hemisphere: this is called the Coriolis effect.  

Capillary waves.

Capillary waves.

When air moves over water, the water’s surface is disturbed. A phenomenon known as capillary waves are formed. These ripples begin the swell generating process. Gravity pulls the ripples downward but they also provide extra surface area for the wind to transfer energy into the water.

As stated before: the stronger the wind, the bigger the area (fetch) and the longer they blow- the bigger the swell. Wind speed is measured by the Beaufort Scale:  from calm- breeze (4-30mph)- gale (31-63mph)- storm (64-72mph)- hurricane (72mph+). With extreme low pressure at their core, hurricanes and tornadoes contain the strongest winds on Earth, sometimes measured between 200-300mph! The planet Neptune has the strongest known winds in the solar system at 1,300mph+. Imagine the swell that would generate!  

Trade winds on the North Shore of Oahu

Trade winds on the North Shore of Oahu.

Prevailing winds are the predominant day to day winds of an area. In general, westerly winds blow across the mid-latitudes and easterly trade winds blow across the tropics. Hawaiian trade winds act like a big air conditioner for the whole island chain. Blowing from the northeast, they blow gently offshore to many famous beaches on the north coasts of the Islands. Kona winds develop from the south when the trades slow down. They often lead to muggy hot weather and volcanic fog (vog) blowing in from Kilauea on the Big Island.

Sea Breeze and land breeze Image: ncsu.edu

Sea Breeze and land breeze.            Image: ncsu.edu

Diurnal temperature variation is responsible for the daily land and sea breeze cycle that impacts many coastlines across the globe. Offshore at first light, perfectly glassy at 9am, onshore- blown out by noon and glassing off as the sun sets. The Ocean remains a more consistent temperature than the land during the day-night cycle. The gradient between land and sea temperatures decreases at night as the land cools down. Land breezes, blowing from the land to the sea, accompany many mornings with favorable surf conditions. As the sun rises and heats the land more than the water, the temp rises and pressure decreases over the land. The sea breeze picks up as air moves from the water to the land, frequently blowing out and negatively impacting surf conditions. As the sun sets, the land cools down and the evening glassoff can occur.  

As coastlines vary, so too the wind’s impact on different surf spots. Nicaragua is known for all-day offshore winds because Lake Nicaragua sits just 10 miles inland and keeps the land breeze blowing most of the day. Regions with bending coastlines can be a blown out mess at one spot while around the corner is offshore. Protected coves can shelter surf spots from wind.  Areas with large kelp beds are less impacted by afternoon onshores because the kelp cuts the wind and smooths the sea surface outside the lineup. Katabatic winds, meaning “downhill,” like Southern California’s Santa Ana winds can change the pattern for days at a time. When fire-free, Santa Ana, offshore winds meet swell at the coastline, SoCal waveriders rejoice.

Santa Ana winds can create magic.

Santa Ana winds can create magic.

 -KS

Sources:
National Center for Atmospheric Research
United Kingdom Meteorological Office
NOAA

Bodysurfing yarns woven 'tween crest & trough