Wind is the movement of air from places where cold air is sinking to places where warm air is rising; it is nature’s way of maintaining equilibrium. This process is wonderfully demonstrated through the sea breeze, a result of land heating and cooling faster then the sea. As the sun rises, the land warms up and hot air rises, creating an area of low air pressure. Colder air from the sea then blows ‘onshore’ to fill the gap; the effect is strongest in the afternoon when the land is hottest. But as the sun sets, the land starts to cool and the colder air blows out to sea to replace the rising warmer air ‘offshore’. This offshore wind is strongest from midnight to dawn, when the land starts to warm up again and the cycle repeats.
The daily cycle of onshore and offshore winds has a huge effect on surfing waves. As a general rule, onshore winds make waves messy and offshore winds keep them clean. Surfers are happiest when the wind is offshore; clean waves are prettier, they last longer and the rides are better. This explains why bleary-eyed surfers are often seen squeezing into wetsuits at the crack of dawn; this is when the winds are best. Technically speaking, they’re actually better in the middle of the night, but a lack of light makes things a little tricky, if not outright dangerous. Inventive minds have toyed with solutions; in the iconic film Point Break the surfers parked their 4x4 on the beach with headlights illuminating the waves. My friend Simon is a fan of glow in the dark dog collars, but this doesn’t help you see when the waves are coming, or what way is up when you’re being tumbled around underwater in the pitch black [except for a gentle glowing from your neck]. In short, until someone comes up with a viable night surfing solution, dawn is best.
ANIMATION: ONSHORE/OFFSHORE WIND ON TIDE
The sea breeze has a profound effect on tides, too. When the wind is offshore it literally pushes back the sea and makes tides lower. In contrast, onshore winds blow water up the beach, making higher tides. On top of this, waves generated by the onshore winds surge up the beach even higher. At times of storm surge risk, the contrasting effects of these two winds can be the tipping point between a serious coastal flooding and a close call; offshore winds would keep the sea away, but onshore winds would enhance the surge. Interestingly, high spring tides [when storm surges happen] in my old hometown of Deal happen at mid-night and mid-day. Following the sea breeze theory, this makes it less likely for a flood to happen at mid-night because there should be an offshore wind.
The theoretical perfection of winds blowing perpendicular to the coast is not always what happens; in practice wind often blows parallel to the shore. We call this a cross-shore wind and if it’s blowing in the same direction the tidal currents are flowing, the sea will be calm. But when the currents turn and start flowing into the wind, the colliding forces create a choppy sea. This makes paddleboarding a challenge, and swimming becomes downright unpleasurable – particularly with front-crawl. There’s nothing worse than coming up for a much-needed gasp of air just as a little wavelet slaps you in the face. The upside of these conditions is that they’re ideal for kitesurfing and windsurfing, because the opposing wind and current make it easy to stay in one place while practicing water starts.
“when currents flow into the wind, the colliding forces create a choppy sea”
The reason coastal winds blow from all quarters is because we are often in the middle of larger, more powerful weather systems than the localised sea breeze. On the greatest scale, Britain is affected by global winds that blow all the way around the world. By understanding the concept of the sea breeze as a ‘cell’, we can apply it to the entire northern hemisphere with three cells at set latitudes. Between the equator [0N] and 30N there is the Hadley Cell, from 30N to 60N is the Ferrell Cell, and the Polar Cell lies between 60N and 90N [The North Pole]. Britain lies around 51 degrees north so is in the Ferrel Cell, where wind is blowing from a band of higher pressure at 30N to a band of lower pressure at 60N. If the world was stationary this wind would blow due north, but the spinning of the earth deflects masses to the right in the northern hemisphere [this is the Coriolis Effect] with the result that Britain’s prevailing global wind is the south-westerly.
This south-westerly wind contributes to powering the Gulf Stream, a warm water current from the Caribbean that flows up Britain’s west coast and keeps our winters mild. Within the current is a stream of creatures hitching a ride and one of the most spectacular is the Portuguese Man-O-War, named because its sail resembles a feared 18th century warship from Portugal. It is this sail catching the south-westerly wind that propels the Man-O-War all the way across the Atlantic to Britain, electrifying unwary beach-goers with its powerful sting.
PRODUCT VIDEO: TIDE WAVE MAP OF THE WORLD
If you do get stung, get out the water immediately and follow the three step guide opposite. We’ve all heard that weeing helps [scientific research disproves this] so it’s up to you to weigh up the probability of success against the emotional scarring of asking your friend [or even worse, a passer by] to wee on you.
ICON: PORTUGEUESE MAN OF WAR
For the ancient mariners who named the Portuguese Man-O-War, the south-westerly winds were both a friend and foe. Because square-rigged ships couldn’t sail ‘into the wind’ like modern yachts, the headwinds when trying to sail down the English Channel into the Atlantic made the journey almost impossible. One ingenious solution was to stow the sails, forget about the wind and travel with the tide instead.
Because the tidal currents flow for six hours at a time up and down the channel, ships would anchor when the current was flowing towards Dover, then drift with the currents when they were heading to Lands End. This technique was called ‘Tiding Over’ and is the origin of the modern term ‘tiding over’ enough cash to keep you solvent until the end-of-month paycheck. But this wouldn’t last long; they were soon out into the Atlantic, flying along with the ‘wind in their sails’. While engines have made this technique obsolete, the same factors make sailing passages more arduous heading west in the Channel, which is why sailors circumnavigating Britain choose the ‘counter-clockwise’ route around, bring them ‘up’ the channel with the prevailing winds.
In the next Sea Signs feature William will reveal the wealth of knowledge you can gain simply by observing air pressure.
About this series
Every day the sea is different, a result of the ever-changing interaction between the moon, sun, tides, wind, waves, buoys, boats and the beach. While the picture may appear complex, like a piece of classical music, it is essentially just an arrangement of simple elements, or notes. By dismantling the machine into its component parts and exploring each one in detail we can create order out of chaos; clarity out of confusion. That is the purpose of this series 'Sea Signs'.
When we are young we learn to navigate urban environments; what traffic lights mean or how to cross a road. What many of us aren’t taught is how to read nature’s signposts; how to judge wind by watching birds or what weather different clouds bring. Then there’s a whole technical world of buoys and boats with different light sequences, colours and signals communicating messages. My goal in this series is to share with you all the signs – both natural and man-made - that you may encounter in your adventures along the coast so you can read them as well as any yachtmaster skipper or crusty old seadog.
With this knowledge, nothing is going to slip under your radar.