“You plan for the knowns. You prepare for the unknowns.”
That is how Ted Metellus, the New York Road Runners’ chief event production officer and race director, describes the challenge of organizing many of New York City’s races.
The distance is known. The course is known. The weather, however, is not.
“You prepare for it as best you can,” Mr. Metellus said.
He oversees the production and logistics of dozens of races each year, including the TCS New York City Marathon.
Weather is “front of line” in the planning, Mr. Metellus said, with heat becoming an increasing focus, especially after an unusually warm marathon in 2022.
That race was an outlier, with temperatures at the Central Park finish about 22 degrees warmer than the year before. The average finishing time was 11 minutes slower, according to data from the Road Runners.
Mr. Metellus said the 2022 race was an important lesson for the organization, prompting it to expand its preparations, including by increasing the number of misting stations ready to deploy regardless of the temperature.
The New York City Marathon has faced the problem before with more extreme consequences. Between 1976 and 1985, the race was held in late October. During the 1984 marathon, the temperature reached 79 degrees with humidity over 90 percent.
Of the 16,315 people who started that race, 14,590 of them crossed the finish line. The New York Times reported that hundreds of runners had been treated for heat-related illnesses. The race also had its first fatality. Jacques Bussereau, a French runner, collapsed in Queens about 14 miles into the event and died later of cardiac arrest. The race founder and director, Fred Lebow, described that marathon as “the disaster of 1984.”
This year, the forecast is for mostly cloudy skies and dry conditions, according to the New York office of the National Weather Service. But temperatures are expected to be abnormally warm for early November, with highs approaching 70 degrees in Central Park on Sunday.
So what kind of conditions allow runners to perform their best?
Research has found that the temperatures associated with the fastest marathon performances vary according to runners’ sex and whether they are elite runners or recreational ones.
A 2012 study examined nearly 1.8 million finishers and looked at how environmental conditions affected performance across six major marathons: Berlin, Boston, Chicago, London, Paris and New York. The researchers looked at temperature, as well as humidity, dew point and atmospheric conditions. They found what many runners knew already: Air temperature has a “major influence” on human running capacity and how runners adapt to conditions on race day.
Among the fastest 1 percent of male runners, the optimum temperature associated with the fastest performance was, on average, 39 degrees; for women, it was 50 degrees. The most favorable temperatures for recreational runners were more even: 43 degrees for men and 44 degrees for women.
Chris Tyler, an associate professor in environmental physiology at the University of Roehampton in London, said the difference was partly because of how much heat runners produced internally.
Faster runners move at a higher intensity and generate more heat inside their bodies, so they perform better in cooler conditions, he said. Slower runners produce less heat and can therefore better tolerate slightly warmer weather. So the higher the outside temperature, the more the internal temperature becomes a problem for performance.
Mike Tipton, a professor of human and applied physiology at the University of Portsmouth, who studies how the body responds to extreme environments, said the body reacted to heat by sending more blood to the skin, where it can be released, while still trying to supply the working muscles.
As blood flow to the skin increases, less blood reaches the working muscles, reducing the oxygen available to them.
The result, Dr. Tipton said, is something familiar to everyone who has run, or tried to run, on a hot day: earlier fatigue and a slower pace. Slowing down reduces the amount of heat the muscles produce and helps bring the body’s demands back within what it can manage.
“Most people who go running will run slower in the heat,” Dr. Tipton said.
For elite runners or just those trying to achieve a personal best, however, slowing down can be difficult.
“Competition drives people, and it can drive them beyond what we would normally regard as a safety limit,” he said.
When the body can no longer compensate for the heat, the consequences can become serious and lead to heat exhaustion or, more severely, heat stroke.
Organizers of the Chicago Marathon learned the consequences of high heat and humidity firsthand in October 2007, when the race was stopped midrun. The air temperature reached 87 degrees, while the dew point remained around 68 degrees from 10 a.m. to 3 p.m, according to the Chicago office of the National Weather Service. The result was a heat index of 90.
More than 300 people were taken from the course by ambulance, many suffering from nausea, dizziness and heart palpitations. Forty-nine people were hospitalized, and a 35-year-old runner who collapsed around the 18th mile later died.
The race became a turning point in how large running events prepared for extreme heat. Starting in 2008, Dr. George Chiampas, the chief medical and safety officer for the Chicago Marathon, said emergency services and other agencies were brought together in a unified command center, where they could coordinate the event in one place. A weather specialist also joined the team, allowing organizers to incorporate forecasts into their planning.
The marathon also introduced its Event Alert System, a color-coded approach to communicate changing weather conditions to runners and race officials. The system has since been adopted by other major marathons, including New York’s, and has become “essentially the cornerstone for running events moving forward,” Dr. Chiampas said.
In Minnesota, organizers have gone one step further: changing the date of the race itself.
Beginning in 2027, the Twin Cities Marathon will move two weeks later from its traditional spot on the first Sunday in October. The decision followed a review of weather data and race conditions, prompted in part by extreme heat that forced organizers to cancel the event in 2023.
That race, on Oct. 1, was the first cancellation in the marathon’s history. The Twin Cities reached 92 degrees that day, the highest temperature ever recorded there in October.
But it wasn’t only the daytime high that organizers considered. Because the marathon begins early in the morning, they also looked at the temperatures around the start of the race.
Ed Whetham, the marathon’s director of event operations, said overnight lows had been “slowly creeping up” over the past 15 years, leaving runners to start the race from a warmer base-line temperature.
The Weather Service office in Minneapolis found a similar pattern. Before 2005, overnight lows above 60 degrees were relatively rare during the first week of October. In three of the past five years, however, there have been at least three days that week when temperatures remained above 60 degrees overnight.
When the Twin Cities Marathon was founded 45 years ago, Dean Orton, president of Twin Cities In Motion, which organizes the race, said the idea was to capture an ideal “crisp fall morning” in Minnesota. But when organizers looked at the weather data and long-term trends, he said, the race was beginning to feel more like a late summer run, with heat and humidity lingering later into the season.
By running the race at a later date, average temperatures are expected to be lower by around 10 degrees, Mr. Orton said.
But moving an event to a cooler time of year is not always an option. For runners, that means preparing for the possibility of heat can be as important as preparing for the distance.
One way to do that is through heat acclimatization, which helps the body adapt to exercising in warmer conditions, Dr. Tyler said.
Dr. Tipton said 10 to 14 days of exercising for about an hour and a half in the heat can help runners adjust to higher temperatures. The body responds by increasing the volume of blood circulating through it, allowing runners to start sweating earlier.
The need to prepare for heat may become more important as temperatures rise.
A 2025 analysis by Climate Central of 221 marathons around the world found that 190 of them (86 percent) were projected by 2045 to have a lower chance of race-day temperatures falling within the range considered optimal for at least one group of elite or recreational runners.
The New York City Marathon is among those races. By 2045, Climate Central’s analysis estimates, the odds of optimal temperatures at that event will have fallen by two to five percentage points for all four groups in the men’s and women’s elite and recreational categories.
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