Today’s forecast for Kona is intimidating all by itself; 33 degrees, 70 per cent humidity, southwesterly gusts of 11 miles per hour. Just the ticket for lounging by the beach and admiring the glint bouncing off the Pacific. Not quite so much if preparing to plunge into the ocean while contemplating prolonged spells yet to come on bike and on foot where every ray of light will seemingly morph instantly into sweat.

David McNamee (almost) wouldn’t have it any other way. Ironman triathlon’s spiritual home is embedded within this Hawaiian idyll and its world championships provide the sport’s ultimate test. 2.4 miles swimming, 112 miles cycling and then a marathon to finish.

“The Tour de France is something else,” the 29-year-old from Ayrshire declares. “It’s over three weeks. But as a one-day event, you can’t really get a tougher challenge than this. Eight and a half hours of flat-out racing in sometimes horrific conditions. With a world title on the line.”

The contest, but also the charm, for an event mythically dreamt up by a US Navy Seal 40 years ago when those who competed in the inaugural edition were incentivised with the opportunity to “brag for the rest of your life."

For the 2000 amateurs – including Edinburgh-based past age-group medallist Ali Rowatt – who have qualified to pit their wits here via a series of global events, little has changed. For professionals, like McNamee, there is prize money and prestige but also, he says, a heightened sense of pushing right up against personal limitations – and then beyond.

“You have the sheer quality of the field,” he outlines. “With most Ironman events you have at most five to 15 really good athletes looking for the podium. Here it is the 50 best in the world, all in the best condition, and that raises the intensity to a whole new level. And there’s the course itself with all the heat and humidity. There’s no one section where you can ease off – in Hawaii it’s full-on for the longest time.”

A rigour much different from the Olympic distance of the sport and from the sprint version that will be utilised in next year’s Commonwealth Games. The Scot, seventh at Glasgow 2014, has firmly left both tracks behind, swapping raw speed for relentless endurance honed at the training base in Catalonia which he shares with Jan Frodeno, who will hope to secure a hat-trick of world crowns by this evening.

The German is one of the few to have conquered all forms of triathlon, having taken Olympic gold in Beijing in 2008. The demands have diverged so much since that any suggestion that McNamee might sign up for Gold Coast 2018 is quickly dismissed. “I’m too slow now. To train for a one-hour event after specialising on this, I’d be ok on the swim and bike but I’d get killed on the run.”

When he moved up in distance three years ago, it also meant erasing his Olympic dreams. There have been occasional whispers of fusing Ironman to the Games programme but little popular backing within the sport, he confirms. “The pinnacle of Ironman is and always will be Hawaii. You don’t want to dilute that. Look at golf coming into the Olympics – a lot of the people would rather win a Major. It’s the same here. I grew up watching this and wanted to win Kona not an Olympic Ironman title.”

Having come eleventh and thirteenth in his initial two ventures into Kona, the podium now feels a tangible goal. McNamee was third in the African Championships earlier this season and then landed three victories at the 70.3km half-Ironman distance with Edinburgh, where he sustained a puncture, providing his only deflation.

Everything, however, has been geared toward here. The past fortnight has been devoted to picking the course apart, familiarisation employed as a means to instil a modicum of comfort. And, still, the trepidation will still be there when he hits the water at 6.30am. Ironman is an examination from beginning to end.

“You can have a bad patch of five minutes where you lose 12 places because the field is so close together. That’s mentally tough. One minute, you can be feeling great and the next you’re feeling awful. The winds can make you go slow and you struggle. But then you turn out of it, you go quicker without doing much, and you feel awesome. Ironman is always a mental challenge but in Kona, there’s the conditions, the course and the fact it’s a world championship. A lot of it is about not giving up mentally before you do physically.”

Onward he will go, steeling himself that the spirit remains strong, that winds are as kind as they can be, that the legs do not buckle. “This is my third time here,” McNamee underlines, “and I understand now just how tough this is.”