COEUR d’ALENE — An Ironman, with 140.6 miles of swimming, biking and running, is difficult.

Add high heat to the mix, and it becomes dangerous.

The weather forecast for this weekend is 99 degrees on Saturday and even hotter on Sunday for Ironman CDA, at 100 degrees.

“If we remain cloudless and it’s over 100 degrees, it’s going to be really tough,” Coeur d’Alene climatologist Cliff Harris said Monday. “The toughest conditions we’ve ever seen for Ironman.”

Ironman Regional Director Dave Christen said they are taking precautions.

“We are focused on making sure the health of the athletes stays in our focus and ensuring that our supply chain and operating teams are ready for the warm day,” he wrote in an email to The Press on Monday.

He said they're enacting a large number of heat protocols. Additional ice, additional hydration, additional support and additional education. He said Ironman will have “more ice and water than people will be able to consume.”

The 2015 Ironman CDA reached 105 degrees and the 2006 race was in the 90s.

“This is not the first time it has got warm on us in CDA so we are lucky that we have an experienced team ready to scale up,” Christen said.

Around 3,000 athletes will face challenging conditions, with the pro men leading things off at 5 a.m. on the 2.4-mile swim in Lake Coeur d’Alene, followed by the pro women at 5:05. The rest of the field will go in waves starting at 5:35 a.m.

The heat will come into play when athletes bike 112 miles, much of the course on U.S. 95 south of Coeur d’Alene, where there is no shade to offer relief from the heat.

It doesn’t get much better when they finish off their day with a 26.2-mile run, which includes the Sanders Beach area and the North Idaho Centennial Trail.

Participants should prepare for the soaring temperatures, Christen said.

”Our advice to athletes will be around rest, hydration and electrolyte focus. Water alone will not be enough for athletes and making sure you have the right mix of water and electrolyte will be important,” he said.

Suzanne Endsley, one of North Idaho’s top triathletes and Ironman veteran, who will be competing Sunday, joked about what awaits her and others.

“Oh boy, aren't we gluttons for punishment!” she wrote.

Endsley said she's had some Ironman failures in the heat and also had success racing in 103 degrees. 

"It's all about throwing out your original plan to have a fast bike and a fast marathon,” she wrote. “Instead, I plan to really dial back the power on the bike, take in as much HEED (electrolyte drink) as I can and primarily go with watery nutrition (gels w/water) to help with digesting in the heat.”

She said she plans to wear a cooling visor and a cooling neck towel on the run and keep getting them wet. She also plans to carry HEED mixed with Endurolyte Extremes in a hand carry bottle with several refill options, which is something she doesn’t normally like to do.

“It’s coming down to survival instead of running fast,” she wrote.

Chicken broth, in a water bottle or gel flask, helps get extra salt in, Endsley wrote.

She added that locals in Sunday’s Ironman tend to “suffer the worst because our wet, cool spring temps don't offer us the opportunity to do any type of heat acclimation. Probably the only good thing about this unusually warm spring is that we locals have been able to do some heat training and that will be helpful. But 100+ is still brutal.”

According to the Centers for Disease Control and Prevention, from 2004 to 2018, there were an average of 702 heat-related deaths (415 with heat as the underlying cause and 287 as a contributing cause) in the United States annually. 

Heatstroke is a concern in the conditions that athletes will compete in on Sunday. It causes the body to overheat "usually as a result of prolonged exposure to or physical exertion in high temperatures. This most serious form of heat injury, heatstroke, can occur if your body temperature rises to 104 F or higher. The condition is most common in the summer months," according to the Mayo Clinic's website.

"Heatstroke requires emergency treatment. Untreated heatstroke can quickly damage your brain, heart, kidneys and muscles. The damage worsens the longer treatment is delayed, increasing your risk of serious complications or death," it said.

Harris said with a high-pressure ridge causing this heatwave and no rain in sight, he’s not expecting the weather forecast to change. He said there's a slight possibility of afternoon clouds, but he's doubtful.

"It’s a tough pattern,” he said, noting that in Arizona, temperatures recently hit 120 degrees.

He said the bike segment of Ironman CDA could be the most difficult, considering the course, the long stretch on U.S. 95, the heat and the dry conditions awaiting athletes late morning into the afternoon.

“It’s going to be mighty tough,” he said.

Harris, too, urged Ironman participants to prepare for dehydration.

“We need to warn people about that,” he said.