When sea breezes cool hot beaches on sweltering days, and when stronger winds cause waves to kick up, we enjoy different experiences beneath the water’s surface. Besides adding to our physical comfort or causing us to marvel at nature’s power, these winds can help us to determine which days are best for diving, as well as which dive site to choose.
Where Wind Comes From and How it Works
Wind is simply air movement in response to temperatures on the earth’s surface, but once it starts to blow, even lightly, more changes take place. As the air moves, it heads toward areas of low pressure from areas of higher pressure, working in concert with the earth’s rotation, centrifugal force, and surface friction to determine its speed. The sun plays a part in this process as well, as its heat directly contributes to pressure differences by heating surface air and causing it to rise. When this happens, new areas of low pressure are created, encouraging air masses to move in.
If you have ever stood and watched clouds moving above you, but felt no air movement around you, you are watching upper air wind in action. When that wind spreads out, surface air rises to replace it, and an area of low pressure forms at the surface. After a while, surface winds pick up again. When you think of wind on a global scale, consider the way various regions are heated and cooled as the seasons pass. Warm air rises from the equatorial region, all the way to about 20,000 feet above the earth’s surface. Then, as it reaches cooler areas, it sinks, and the cycle starts all over again. Wind patterns are complicated and they create complicated climate and weather patterns, but they can often be counted on – just think of the trade winds early sailors relied on for seasonal travel. Local sea breezes work just like global weather patterns, but on a smaller scale; on sunny days, the wind picks up in the afternoon as warm air rises and cooler air sinks to replace it.
How Wind affects Diving
Wind affects diving in many different ways. The most noticeable way is by the creation of waves as it runs across the water’s surface, creating ripples or chop, or contributing to larger sea swells. You can see this in action on days when the water’s surface changes from glassy to choppy as air temperatures change; once you begin to see a bit of white as wind speed increases to speeds between 11 and 16 knots, you’ll know that it’s time to wait for smoother conditions before attempting a dive. The harder the wind is blowing, the more turbulent the upper layer of water will be, and the more difficult surface swimming will be, unless you’re blessed with a wind that is pushing the water in the direction you need to go.
Familiarizing yourself with the Beaufort Scale and learning about linear wave characteristics can help you determine what conditions will be like underwater. In recreational diving depths, when waves at the surface increase, surge at the bottom increases as well, which not only affects the amount of effort divers must expend, it also affects visibility in areas with sandy or silty bottoms. The best weather for diving occurs when surface pressure is stable, with no extreme highs or lows, and when temperatures are stable as well; in other words, when winds are calm, it’s probably the ideal time to dive.