Fu­ri­ous 122km/h swells ...

Weekend Argus (Saturday Edition) - - SPORT - STEVE PIKE

WHAT a strange sum­mer we have had. Not only has the south­easter been scarce, but we’ve had a lot of cooler weather, with plenty of cloud and even some wel­come rain.

When the Cape Doc­tor has blown, even in the peak of sum­mer, it has blown more southerly, a wind di­rec­tion nor­mally as­so­ci­ated with au­tumn as the South At­lantic high be­gins to move north, and the on­com­ing low pres­sure sys­tems shift into the breech, caus­ing the preva­lent winds to shift from SE to SW, punc­tu­ated by in­creas­ingly more reg­u­lar bursts of NW.

But what re­ally brought home weather pat­terns that in the words of Al­ice in Won­der­land are be­com­ing “cu­ri­ouser and cu­ri­ouser” was the groundswell we grate­fully re­ceived this week af­ter a long and slow flat spell.

An un­usu­ally fierce sum­mer storm about 2000 nau­ti­cal miles from Cape Town peaked last week Fri­day with core winds across a fetch of about 500 miles blast­ing to 80 knots, which is more than dou­ble gale-force.

From the end of this con­veyor belt of wind marched a swell that had fore­cast­ers such as me ‘froth­ing’ with ex­cite­ment, as younger surfers might say. The rea­son for the ex­cite­ment, shared by many surfers around the Cape, was some­thing that even in win­ter is as rare as fos­silized hens’ teeth from the Protero­zoic eon.

The un­usual at­tribute was all about in­ter­val. Af­ter ra­di­at­ing out from the gi­gan­tic pres­sure bomb that went off in the deep, the swells took three days to reach us, and when they did, each oc­curred ev­ery 22 sec­onds, other­wise known as wave pe­riod. Swells from hur­ri­cane-force storm winds are the most pow­er­ful, cer­tainly in terms of those formed by wind. To look for any­thing more pow­er­ful, you have to look at other types of orig­i­nat­ing force, such as un­der­sea earthquakes or space de­bris slam­ming into the ocean.

A 22-sec­ond swell, which is a man­i­fes­ta­tion of the wind ve­loc­ity that cre­ated it – has a math­e­mat­i­cally con­stant wave­length of 755 me­tres. On top of all this vol­ume of ocean that is be­ing moved as the swell glides through it, ex­tremely long swells have mas­sively ex­po­nen­tially more en­ergy than shorter pe­riod swells, and they’re mov­ing at in­cred­i­ble speeds.

An in­di­vid­ual 22-sec­ond swell moves through the ocean at 122 km/h. When it reaches the coast, this en­ergy and speed are ex­pressed in the sheer vol­ume and power of the even­tual wave that breaks. Even small waves at these pe­ri­ods are in­or­di­nately pow­er­ful, of­ten mov­ing too fast for our puny arms to catch them. Early Mon­day, an in­trepid group of surfers in the deep south ex­pe­ri­enced this. At a pow­er­ful reef break, they waited for the sets to come for up to 20 min­utes, and then got caught up in a mad blast of ocean power they strug­gled to deal with.

Un­usu­ally spaced long pe­riod swells pose the most dan­ger to ter­res­tri­ally based peo­ple be­cause of their de­cep­tion. A fish­er­man could lit­er­ally un­pack his box of tricks, bait up, and clam­ber over to a rock, with the mis­taken be­lief that the sea is flat.

These lulls also make long pe­riod swell con­tro­ver­sial to surfers. The surfers who watched their spot for 15 min­utes and left will claim the ocean was flat to friends who will smugly claim other­wise. While this par­tic­u­lar swell was smaller than I thought, the en­ergy was in­sane when the sets came on Mon­day. By Tues­day, I pad­dled out at the same reef break, and even though the pe­riod had eased, I saw sev­eral waves of im­mense power. With the vol­ume and power be­hind it, a swell can quadru­ple in size. Some wave faces were eas­ily four or five times over­head.

Many surf­boards were bro­ken in the car­nage, and some peo­ple paid their dues in the im­pact zone. It was fas­ci­nat­ing to be part of it.

WEATHER TIP

A lovely burst of cooler NW wind and some rain overnight to­day brings a solid 6-8 foot swell in light to calm NW left­overs from the fierce burst of win­tery weather yes­ter­day. The NW goes mod­er­ate to fresh to­day, break­ing up the sea but Muizen­berg looks su­per fun 3’ and clean off­shore. To­mor­row, a new swell builds to a solid 8 foot by dusk in mod­er­ate to fresh NW. An­other great surf day for Muizen­berg.

WSL / Ces­tari

Long pe­riod swells move with such power and speed, some­times they are hard to catch. Ryan Cal­li­nan wipes out at Pipe­line, Hawaii, at the Pipe­line In­vi­ta­tional he won in De­cem­ber. /

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