After the 2020 Bank of America Chicago Marathon was canceled because of the pandemic, many runners looked ahead to the 2021 race.

       But runners should beware of intense heat this year as temperatures are expected to peak at 81 degrees Sunday, according to the National Weather Service.

       Jake Petr, a weather service meteorologist, said the normal high temperature for Oct. 10 in Chicago is about 65 degrees, putting Sunday well above the norm.

       When the first wave of runners begin at 7:30 a.m., the temperature will be near 70 degrees and will hit the upper 70s around noon when many runners will still be on the course. The mercury will continue to rise into the 80s in the afternoon, forecasters say.

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       Veteran runners still remember the extreme heat that prematurely ended the 2007 Chicago Marathon and sent over 300 runners to the hospital.

       Longtime marathon runner and coach Denise Sauriol said she “survived” the marathon in 2007, when temperatures reached 89 degrees. This Sunday will mark her 125th marathon and her 26th Chicago Marathon.

       Scott Sexton, of Stevens Point, Wisconsin, has his medal and a bag of ice on his head at the finish of the 30th LaSalle Bank Chicago Marathon in 2007, which was cut short because of the heat-related stresses and injuries to runners. (Chuck Berman / Chicago Tribune)

       While running to Sauriol is “life-igniting,” she also said the goal is to keep safe and to stay out of the medical tent.

       “When we exercise, our body generates heat,” Sauriol said. “The rule in running is whatever the temperature is outside you add 20 degrees to that.”

       Sauriol said the ideal temperature for her is between 50 and 55 degrees. While spectators at the White Sox playoff game at 7 p.m. might enjoy the high temperatures, Sauriol said anything above 70 degrees is dangerous for runners.

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       According to Bill Snyder, WGN’s weather producer, this October has been a trend-breaking month.

       “It’s been 142 years (1879) since an October logged this many consecutive days with low temps 60°+,” Snyder wrote on Twitter. “Remarkable considering the NORMAL low this time of year is in the upper 40s.”

       And these high temperatures may continue into next week.

       Sanja Pantic, right, brought out her garden house from her home on the 1500 block of West Jackson Blvd. to give water to marathon runners at the 2007 Lasalle Bank Chicago Marathon on Oct. 7, 2007. The runners were between mile 15 and 16. (Jos M. Osorio / Chicago Tribune)

       Sauriol, who has 160 running students in the marathon, said she recommends carrying a small Ziploc bag that runners can fill with ice as they move through the course. By pressing the bag to their wrists and neck, runners can keep their body temperature lower.

       Sauriol also recommended wearing light-colored clothing and drinking plenty of electrolytes leading up to the race.

       Most importantly, however, Sauriol said the goal of Sunday’s marathon should be to finish, not to beat the clock.

       “Run, don’t race.” Sauriol said. “Just remember that there are all kinds of races, and there is only one you, so just be careful.”

       While Sunday may see higher temperatures than normal, Thursday and Friday will have periods of heavy downpours that will keep the daily highs in the mid-70s.

       The rest of the weekend will be “breezy,” according to the weather service, with temperatures in the 70s and low 80s, which will may ideal for everyone — except runners in the marathon.

       sygoodman@chicagotribune.com

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